title: Chirality (chemistry)

text: The chirality of a molecule is based on the molecular symmetry of its conformations. A conformation of a molecule is chiral if and only if it belongs to the "C", "D", "T", "O", "I" point groups (the chiral point groups). However, whether the molecule itself is considered to be chiral depends on whether its chiral conformations are persistent isomers that could be isolated as separated enantiomers, at least in principle, or the enantiomeric conformers rapidly interconvert at a given temperature and timescale through low-energy conformational changes (rendering the molecule achiral). For example, despite having chiral "gauche" conformers that belong to the "C" point group, butane is considered achiral at room temperature because rotation about the central C–C bond rapidly interconverts the enantiomers (3.4 kcal/mol barrier). Similarly, "cis"-1,2-dichlorocyclohexane consists of chair conformers that are nonidentical mirror images, but the two can interconvert via the cyclohexane chair flip (~10 kcal/mol barrier). As another example, amines with three distinct substituents (RRRN:) are also regarded as achiral molecules because their enantiomeric pyramidal conformers rapidly invert and interconvert through a planar transition state (~6 kcal/mol barrier).


title: Chirality (chemistry)

text: However, if the temperature in question is low enough, the process that interconverts the enantiomeric chiral conformations becomes slow compared to a given timescale. The molecule would then be considered to be chiral at that temperature. The relevant timescale is, to some degree, arbitrarily defined: 1000 seconds is sometimes employed, as this is regarded as the lower limit for the amount of time required for chemical or chromatographic separation of enantiomers in a practical sense. Molecules that are chiral at room temperature due to restricted rotation about a single bond (barrier to rotation ≥ ca. 23 kcal/mol) are said to exhibit atropisomerism.


title: Chirality (chemistry)

text: A chiral compound can contain no improper axis of rotation ("S"), which includes planes of symmetry and inversion center. Chiral molecules are always dissymmetric (lacking "S") but not always asymmetric (lacking all symmetry elements except the trivial identity). Asymmetric molecules are always chiral.


title: Chirality (chemistry)

text: The following table shows some examples of chiral and achiral molecules, with the Schoenflies notation of the point group of the molecule. In the achiral molecules, X and Y (with no subscript) represent achiral groups, whereas X and X or Y and Y represent enantiomers. Note that there is no meaning to the orientation of an "S" axis, which is just an inversion. Any orientation will do, so long as it passes through the center of inversion. Also note that higher symmetries of chiral and achiral molecules also exist, and symmetries that do not include those in the table, such as the chiral "C" or the achiral "S".


title: Chirality (chemistry)

text: Many chiral molecules have point chirality, namely a single chiral stereogenic center that coincides with an atom. This stereogenic center usually has four or more bonds to different groups, and may be carbon (as in many biological molecules), phosphorus (as in many organophosphates), silicon, or a metal (as in many chiral coordination compounds). However, a stereogenic center can also be a trivalent atom whose bonds are not in the same plane, such as phosphorus in P-chiral phosphines (PRR′R″) and sulfur in S-chiral sulfoxides (OSRR′), because a lone-pair of electrons is present instead of a fourth bond.


title: Chirality (chemistry)

text: Chirality can also arise from isotopic differences between atoms, such as in the deuterated benzyl alcohol PhCHDOH; which is chiral and optically active (["α"] = 0.715°), even though the non-deuterated compound PhCHOH is not.


title: Chirality (chemistry)

text: If two enantiomers easily interconvert, the pure enantiomers may be practically impossible to separate, and only the racemic mixture is observable. This is the case, for example, of most amines with three different substituents (NRR′R″), because of the low energy barrier for nitrogen inversion.


title: Chirality (chemistry)

text: While the presence of a stereogenic center describes the great majority of chiral molecules, many variations and exceptions exist. For instance it is not necessary for the chiral substance to have a stereogenic center. Examples include 1-bromo-3-chloro-5-fluoroadamantane, methylethylphenyltetrahedrane, certain calixarenes and fullerenes, which have inherent chirality. The C-symmetric species 1,1′-bi-2-naphthol (BINOL), 1,3-dichloroallene have axial chirality. ("E")-cyclooctene and many ferrocenes have planar chirality.


title: Chirality (chemistry)

text: When the optical rotation for an enantiomer is too low for practical measurement, the species is said to exhibit cryptochirality.


title: Chirality (chemistry)

text: Chirality is an intrinsic part of the identity of a molecule, so the systematic name includes details of the absolute configuration ("R/S", "", or other designations).


title: Chirality (chemistry)

text: Many biologically active molecules are chiral, including the naturally occurring amino acids (the building blocks of proteins) and sugars.


title: Chirality (chemistry)

text: The origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. However, there is some suggestion that early amino acids could have formed in comet dust. In this case, circularly polarised radiation (which makes up 17% of stellar radiation) could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which ultimately resulted in all life on Earth being homochiral.


title: Chirality (chemistry)

text: Enzymes, which are chiral, often distinguish between the two enantiomers of a chiral substrate. One could imagine an enzyme as having a glove-like cavity that binds a substrate. If this glove is right-handed, then one enantiomer will fit inside and be bound, whereas the other enantiomer will have a poor fit and is unlikely to bind.


title: Chirality (chemistry)

text: -forms of amino acids tend to be tasteless, whereas -forms tend to taste sweet. Spearmint leaves contain the -enantiomer of the chemical carvone or "R"-(−)-carvone and caraway seeds contain the -enantiomer or "S"-(+)-carvone. The two smell different to most people because our olfactory receptors are chiral.


title: Chirality (chemistry)

text: Chirality is important in context of ordered phases as well, for example the addition of a small amount of an optically active molecule to a nematic phase (a phase that has long range orientational order of molecules) transforms that phase to a chiral nematic phase (or cholesteric phase). Chirality in context of such phases in polymeric fluids has also been studied in this context.


title: Chirality (chemistry)

text: Chirality is a symmetry property, not a property of any part of the periodic table. Thus many inorganic materials, molecules, and ions are chiral. Quartz is an example from the mineral kingdom. Such noncentric materials are of interest for applications in nonlinear optics.


title: Chirality (chemistry)

text: In the areas of coordination chemistry and organometallic chemistry, chirality is pervasive and of practical importance. A famous example is tris(bipyridine)ruthenium(II) complex in which the three bipyridine ligands adopt a chiral propeller-like arrangement. The two enantiomers of complexes such as [Ru(2,2′-bipyridine)] may be designated as Λ (capital lambda, the Greek version of "L") for a left-handed twist of the propeller described by the ligands, and Δ (capital delta, Greek "D") for a right-handed twist (pictured). Also cf. dextro- and levo- (laevo-).


title: Chirality (chemistry)

text: Chiral ligands confer chirality to a metal complex, as illustrated by metal-amino acid complexes. If the metal exhibits catalytic properties, its combination with a chiral ligand is the basis of asymmetric catalysis.


title: Chirality (chemistry)

text: The term "optical activity" is derived from the interaction of chiral materials with polarized light. In a solution, the (−)-form, or levorotatory form, of an optical isomer rotates the plane of a beam of linearly polarized light counterclockwise. The (+)-form, or dextrorotatory form, of an optical isomer does the opposite. The rotation of light is measured using a polarimeter and is expressed as the optical rotation.


title: Chirality (chemistry)

text: Enantiomers can be separated by chiral resolution. This often involves forming crystals of a salt composed of one of the enantiomers and an acid or base from the so-called chiral pool of naturally occurring chiral compounds, such as malic acid or the amine brucine. Some racemic mixtures spontaneously crystallize into right-handed and left-handed crystals that can be separated by hand. Louis Pasteur used this method to separate left-handed and right-handed sodium ammonium tartrate crystals in 1849. Sometimes it is possible to seed a racemic solution with a right-handed and a left-handed crystal so that each will grow into a large crystal.


title: Chirality (chemistry)

text: Liquid chromatography (HPLC and TLC) may also used as an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients (APIs) which are chiral.


title: Chirality (chemistry)

text: The rotation of plane polarized light by chiral substances was first observed by Jean-Baptiste Biot in 1812, and gained considerable importance in the sugar industry, analytical chemistry, and pharmaceuticals. Louis Pasteur deduced in 1848 that this phenomenon has a molecular basis. The term "chirality" itself was coined by Lord Kelvin in 1894. Different enantiomers or diastereomers of a compound were formerly called optical isomers due to their different optical properties. At one time, chirality was thought to be restricted to organic chemistry, but this misconception was overthrown by the resolution of a purely inorganic compound, a cobalt complex called hexol, by Alfred Werner in 1911.


title: Chirality (chemistry)

text: In the early 1970s, various groups established that the human olfactory organ is capable of distinguishing chiral compounds.


title: Loan

text: In finance, a loan is the lending of money by one or more individuals, organizations, or other entities to other individuals, organizations, etc. The recipient (i.e., the borrower) incurs a debt and is usually liable to pay interest on that debt until it is repaid as well as to repay the principal amount borrowed.


title: Loan

text: The document evidencing the debt (e.g., a promissory note) will normally specify, among other things, the principal amount of money borrowed, the interest rate the lender is charging, and the date of repayment. A loan entails the reallocation of the subject asset(s) for a period of time, between the lender and the borrower.


title: Loan

text: The interest provides an incentive for the lender to engage in the loan. In a legal loan, each of these obligations and restrictions is enforced by contract, which can also place the borrower under additional restrictions known as loan covenants. Although this article focuses on monetary loans, in practice, any material object might be lent.


title: Loan

text: Acting as a provider of loans is one of the main activities of financial institutions such as banks and credit card companies. For other institutions, issuing of debt contracts such as bonds is a typical source of funding.


title: Loan

text: A secured loan is a form of debt in which the borrower pledges some asset (i.e., a car, a house) as collateral.


title: Loan

text: A mortgage loan is a very common type of loan, used by many individuals to purchase residential or commercial property. The lender, usually a financial institution, is given security a lien on the title to the property until the mortgage is paid off in full. In the case of home loans, if the borrower defaults on the loan, the bank would have the legal right to repossess the house and sell it, to recover sums owing to it.


title: Loan

text: Similarly, a loan taken out to buy a car may be secured by the car. The duration of the loan is much shorter often corresponding to the useful life of the car. There are two types of auto loans, direct and indirect. In a direct auto loan, a bank lends the money directly to a consumer. In an indirect auto loan, a car dealership (or a connected company) acts as an intermediary between the bank or financial institution and the consumer.


title: Loan

text: Other forms of secured loans include loans against securities – such as shares, mutual funds, bonds, etc. This particular instrument issues customers a line of credit based on the quality of the securities pledged. Gold loans are issued to customers after evaluating the quantity and quality of gold in the items pledged. Corporate entities can also take out secured lending by pledging the company's assets, including the company itself. The interest rates for secured loans are usually lower than those of unsecured loans. Usually, the lending institution employs people (on a roll or on a contract basis) to evaluate the quality of pledged collateral before sanctioning the loan.


title: Loan

text: Unsecured loans are monetary loans that are not secured against the borrower's assets. These may be available from financial institutions under many different guises or marketing packages:


title: Loan

text: The interest rates applicable to these different forms may vary depending on the lender and the borrower. These may or may not be regulated by law. In the United Kingdom, when applied to individuals, these may come under the Consumer Credit Act 1974.


title: Loan

text: Interest rates on unsecured loans are nearly always higher than for secured loans because an unsecured lender's options for recourse against the borrower in the event of default are severely limited, subjecting the lender to higher risk compared to that encountered for a secured loan. An unsecured lender must sue the borrower, obtain a money judgment for breach of contract, and then pursue execution of the judgment against the borrower's unencumbered assets (that is, the ones not already pledged to secured lenders). In insolvency proceedings, secured lenders traditionally have priority over unsecured lenders when a court divides up the borrower's assets. Thus, a higher interest rate reflects the additional risk that in the event of insolvency, the debt may be uncollectible.


title: Loan

text: Demand loans are short-term loans that typically do not have fixed dates for repayment. Instead, demand loans carry a floating interest rate, which varies according to the prime lending rate or other defined contract terms. Demand loans can be "called" for repayment by the lending institution at any time. Demand loans may be unsecured or secured.


title: Loan

text: A subsidized loan is a loan on which the interest is reduced by an explicit or hidden subsidy. In the context of college loans in the United States, it refers to a loan on which no interest is accrued while a student remains enrolled in education.


title: Loan

text: A concessional loan, sometimes called a "soft loan", is granted on terms substantially more generous than market loans either through below-market interest rates, by grace periods, or a combination of both. Such loans may be made by foreign governments to developing countries or may be offered to employees of lending institutions as an employee benefit (sometimes called a "perk").


title: Loan

text: Loans can also be categorized according to whether the debtor is an individual person (consumer) or a business.


title: Loan

text: Common personal loans include mortgage loans, car loans, home equity lines of credit, credit cards, installment loans, and payday loans. The credit score of the borrower is a major component in and underwriting and interest rates (APR) of these loans. The monthly payments of personal loans can be decreased by selecting longer payment terms, but overall interest paid increases as well. A personal loan can be obtained from banks, alternative (non-bank) lenders, online loan providers and private lenders.


title: Loan

text: Loans to businesses are similar to the above but also include commercial mortgages and corporate bonds and government guaranteed loans Underwriting is not based upon credit score but rather credit rating.


title: Loan

text: The most typical loan payment type is the fully amortizing payment in which each monthly rate has the same value over time.


title: Loan

text: Predatory lending is one form of abuse in the granting of loans. It usually involves granting a loan in order to put the borrower in a position that one can gain advantage over them; subprime mortgage-lending and payday-lending are two examples, where the moneylender is not authorized or regulated, the lender could be considered a loan shark.


title: Loan

text: Usury is a different form of abuse, where the lender charges excessive interest. In different time periods and cultures, the acceptable interest rate has varied, from no interest at all to unlimited interest rates. Credit card companies in some countries have been accused by consumer organizations of lending at usurious interest rates and making money out of frivolous "extra charges".


title: Loan

text: Abuses can also take place in the form of the customer defrauding the lender by borrowing without intending to repay the loan.


title: Loan

text: Most of the basic rules governing how loans are handled for tax purposes in the United States are codified by both Congress (the Internal Revenue Code) and the Treasury Department (Treasury Regulations another set of rules that interpret the Internal Revenue Code).


title: Loan

text: 1. A loan is not gross income to the borrower. Since the borrower has the obligation to repay the loan, the borrower has no accession to wealth.


title: Loan

text: 2. The lender may not deduct (from own gross income) the amount of the loan. The rationale here is that one asset (the cash) has been converted into a different asset (a promise of repayment). Deductions are not typically available when an outlay serves to create a new or different asset.


title: Loan

text: 3. The amount paid to satisfy the loan obligation is not deductible (from own gross income) by the borrower.


title: Loan

text: 4. Repayment of the loan is not gross income to the lender. In effect, the promise of repayment is converted back to cash, with no accession to wealth by the lender.


title: Loan

text: 5. Interest paid to the lender is included in the lender's gross income. Interest paid represents compensation for the use of the lender's money or property and thus represents profit or an accession to wealth to the lender. Interest income can be attributed to lenders even if the lender doesn't charge a minimum amount of interest.


title: Loan

text: 6. Interest paid to the lender may be deductible by the borrower. In general, interest paid in connection with the borrower's business activity is deductible, while interest paid on personal loans are not deductible. The major exception here is interest paid on a home mortgage.


title: Loan

text: Although a loan does not start out as income to the borrower, it becomes income to the borrower if the borrower is discharged of indebtedness. Thus, if a debt is discharged, then the borrower essentially has received income equal to the amount of the indebtedness. The Internal Revenue Code lists "Income from Discharge of Indebtedness" in Section 61(a)(12) as a source of gross income.


title: Loan

text: Example: X owes Y $50,000. If Y discharges the indebtedness, then X no longer owes Y $50,000. For purposes of calculating income, this is treated the same way as if Y gave X $50,000.


title: Loan

text: For a more detailed description of the "discharge of indebtedness", look at Section 108 (Cancellation of Debt (COD) Income) of the Internal Revenue Code.


title: Thermoplastic

text: A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.


title: Thermoplastic

text: Most thermoplastics have a high molecular weight. The polymer chains associate by intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. In this state, thermoplastics may be reshaped and are typically used to produce parts by various polymer processing techniques such as injection molding, compression molding, calendering, and extrusion. Thermoplastics differ from thermosetting polymers (or "thermosets"), which form irreversible chemical bonds during the curing process. Thermosets do not melt when heated, but typically decompose and do not reform upon cooling.


title: Thermoplastic

text: Above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below the glass transition temperature, retaining some or all of their amorphous characteristics. Amorphous and semi-amorphous plastics are used when high optical clarity is necessary, as light is scattered strongly by crystallites larger than its wavelength. Amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure.


title: Thermoplastic

text: Brittleness can be decreased with the addition of plasticizers, which increases the mobility of amorphous chain segments to effectively lower the glass transition temperature. Modification of the polymer through copolymerization or through the addition of non-reactive side chains to monomers before polymerization can also lower it. Before these techniques were employed, plastic automobile parts would often crack when exposed to cold temperatures. These are linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling.


title: Thermoplastic

text: Today’s acrylics industry can be divided into two distinct multibillion-dollar markets: on one hand the polyacrylic acids (PAA) and its ester derivatives (PAc) market, on the other hand, the poly(methyl methacrylate) (PMMA) market. PMMA is also known by trade names such as Lucite, Perspex and Plexiglas. It serves as a sturdy substitute for glass for items such as aquariums, buttons, motorcycle helmet visors, aircraft windows, viewing ports of submersibles, and lenses of exterior lights of automobiles. It is extensively used to make signs, including lettering and logos. In medicine, it is used in bone cement and to replace eye lenses. Acrylic paint consists of PMMA particles suspended in water.


title: Thermoplastic

text: For many decades, PMMA has been the predominant methacrylic ester produced worldwide. Major players in the PMMA market are Mitsubishi Rayon (Japan), Arkema SA (France), LG MMA (South Korea), Chi Mei Corp. (Taiwan), Sumimoto Chemical Company Ltd (Japan), Evonik Industries (Germany), BASF (Germany), Dow Chemical Company (U.S.), AkzoNobel (The Netherlands), Quinn Plastics (UK) and Cytec Industries (U.S.). Regarding the PAA and PAc market, key manufacturers are Nippon Shokubai Company Ltd. (Japan), Arkema SA (France) and Dow Chemical Company (U.S.)


title: Thermoplastic

text: Acrylonitrile butadiene styrene (ABS) is a terpolymer synthesized from styrene and acrylonitrile in the presence of polybutadiene. ABS is a light-weight material that exhibits high impact resistance and mechanical toughness. It poses few risks to human health under normal handling. It is used in many consumer products, such as toys, appliances, and telephones.


title: Thermoplastic

text: Nylon belongs to a class of polymers called polyamides. It has served as a substitute mainly for hemp, cotton and silk, in products such as parachutes, cords, sails, flak vests and clothing. Nylon fibres are useful in making fabrics, rope, carpets and musical strings, whereas, in bulk form, nylon is used for mechanical parts including machine screws, gears and power tool casings. In addition, it is used in the manufacture of heat-resistant composite materials.


title: Thermoplastic

text: Polylactic acid (polylactide) is a compostable thermoplastic aliphatic polyester derived from renewable resources, such as corn starch (in the United States), sugar beet pulp (in Europe), tapioca roots, chips or starch (mostly in Asia), or sugarcane. It is the most common material used for 3D printing with fused deposition modeling (FDM) techniques.


title: Thermoplastic

text: Polybenzimidazole (PBI, short for Poly-[2,2’-(m-phenylen)-5,5’-bisbenzimidazole]) fiber is a synthetic fiber with a very high melting point. It has exceptional thermal and chemical stability and does not readily ignite. It was first discovered by American polymer chemist Carl Shipp Marvel in the pursuit of new materials with superior stability, retention of stiffness, toughness at elevated temperature. Due to its high stability, Polybenzimidazole is used to fabricate high-performance protective apparel such as firefighter's gear, astronaut space suits, high temperature protective gloves, welders’ apparel and aircraft wall fabrics. In recent years, polybenzimidazole found its application as membrane in fuel cells.


title: Thermoplastic

text: Polycarbonate (PC) thermoplastics are known under trademarks such as Lexan, Makrolon, Makroclear, and arcoPlus. They are easily worked, molded, and thermoformed for many applications, such as electronic components, construction materials, data storage devices, automotive and aircraft parts, check sockets in prosthetics, and security glazing. Polycarbonates do not have a unique resin identification code. Items made from polycarbonate can contain the precursor monomer bisphenol A (BPA). Susceptible to UV light, exposure results in yellowing (degradation is especially visible in headlamps that lost or didn't have proper protective coating).


title: Thermoplastic

text: Polyether sulfone (PES) or polysulfone is a class of specially engineered thermoplastics with high thermal, oxidative, and hydrolytic stability, and good resistance to aqueous mineral acids, alkalis, salt solutions, oils and greases.


title: Thermoplastic

text: Polyoxymethylene (POM), also known as acetal, polyacetal and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Celcon, Ramtal, Duracon, Kepital and Hostaform.


title: Thermoplastic

text: Polyether ether ketone(PEEK) is a colourless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. It was originally introduced by Victrex PLC, then ICI (Imperial Chemical Industries) in the early 1980s. It has attractive properties like good abrasion resistance, low flammability and emission of smoke and toxic gases.


title: Thermoplastic

text: Polyetherimide (PEI), produced by a novel nitro displacement reaction involving bisphenol A, 4, 4’-methylenedianiline and 3-nitrophthalic anhydride, has high heat distortion temperature, tensile strength and modulus. They are generally used in high performance electrical and electronic parts, microwave appliances, and under-the-hood automotive parts.


title: Thermoplastic

text: Polyethylene (polyethene, polythene, PE) is a family of similar materials categorized according to their density and molecular structure. It is also known as poly and is obtained by the addition polymerisation of ethylene. It may be of low density or high density depending upon the process used in its manufacturing. It is resistant to moisture and most of the chemicals. It is flexible at room temperature (and low temperature) and can be heat sealed. Since it is an inexpensive plastic it is made in large amounts to cater to the demand. For example:


title: Thermoplastic

text: Polyphenylene oxide (PPO), which is obtained from the free-radical, step-growth oxidative coupling polymerization of 2,6-xylenol, has many attractive properties such as high heat distortion and impact strength, chemical stability to mineral and organic acids, and low water absorption. PPO is difficult to process, and hence the commercial resin (Noryl) is made by blending PPO with high-impact polystyrene (HIPS), which serves to reduce the processing temperature.


title: Thermoplastic

text: Polyphenylene sulfide (PPS) obtained by the condensation polymerization of p-dichlorobenzene and sodium sulfide, has outstanding chemical resistance, good electrical properties, excellent flame retardance, low coefficient of friction and high transparency to microwave radiation. PPS is principally used in coating applications. This is done by spraying an aqueous slurry of PPS particles and heating to temperatures above 370 °C. Particular grades of PPS can be used in injection and compression molding at temperatures (300 to 370 °C) at which PPS particles soften and undergo apparent crosslinking. Principal applications of injection and compression molded PPS include cookware, bearings, and pump parts for service in various corrosive environments.


title: Thermoplastic

text: Polypropylene (PP) is useful for such diverse products as reusable plastic food containers, microwave- and dishwasher-safe plastic containers, diaper lining, sanitary pad lining and casing, ropes, carpets, plastic moldings, piping systems, car batteries, insulation for electrical cables and filters for gases and liquids. In medicine, it is used in hernia treatment and to make heat-resistant medical equipment. Polypropylene sheets are used for stationery folders and packaging and clear storage bins. Polypropylene is defined by the recyclable plastic number 5. Although relatively inert, it is vulnerable to ultraviolet radiation and can degrade considerably in direct sunlight. Polypropylene is not as impact-resistant as the polyethylenes (HDPE, LDPE). It is also somewhat permeable to highly volatile gases and liquids.


title: Thermoplastic

text: Polystyrene is manufactured in various forms that have different applications and can have medium to very low density. Extruded polystyrene (PS or xPS, sometimes colored pink/blue) is used in the manufacture of disposable cutlery, rigid ground contact rated insulating foam board, CD and DVD cases, plastic models of cars and boats, and smoke detector housings. Expanded polystyrene foam (EPS or "styrofoam", white) is used in making insulation and packaging materials, such as the "peanuts" and molded foam used to cushion fragile products. Polystyrene copolymers are used in the manufacture of toys and product casings.


title: Thermoplastic

text: Polyvinyl chloride (PVC) is a tough, lightweight material that is durable, fairly rigid and versatile, and is resistant to acids and bases. Much of it is used by the construction industry, such as for vinyl siding, drainpipes, gutters and roofing sheets. It is also converted to flexible forms with the addition of plasticizers, thereby making it useful for items such as hoses, tubing, electrical insulation, coats, jackets and upholstery. Flexible PVC is also used in inflatable products, such as water beds and pool toys. PVC is also a common material in vinyl action figures, especially in countries such as Japan, where the material is used extensively in so-called Sofubi figures (Soft vinyl toys). As PVC bends easily and has a tendency to be bent during transit, a method to mitigate this deformation is to heat the plastic until it becomes mobile, then reform the material into the desired shape.


title: Thermoplastic

text: PVC is produced in many specific modifications to affect its chemical and physical properties. In plasticized polyvinyl chloride (pPVC), plasticizers are added to the raw material before molding to make it more flexible or pliable. Early on, the health and environmental aspects of this were poorly understood and replacements and product bans resulted after studies. The original form is often referred to as unplasticized polyvinyl chloride (uPVC), which is the more commonly used type for installations such as water, waste, and sewer conveyance plumbing.


title: Thermoplastic

text: Chemical modification often produces more drastic changes in properties. Chlorinated polyvinyl chloride (CPVC) is produced through exposing PVC to the continued free-radical chlorination reaction that originally formulates the PVC polymer. The chlorination reaction continues to add chlorine atoms to the polymer hydrocarbon backbone until most commercial applications reach a percent range between 56 and 74% total chlorine. This increase in elemental chlorine content contributes to CPVC's increased expression of chlorine-based characteristics, such as chemical durability, resistance to acids, bases, and salts; susceptibility to ammonia-based compounds, aromatics, esters, ketones; chemical stability; heat energy transfer resistance. CPVC is commonly used in water, chemical, hot and cold, delivery systems for residential, commercial, and industrial applications.


title: Thermoplastic

text: Polyvinylidene fluoride, PVDF, belongs to the fluoropolymer class of thermoplastics and is known for its high chemical inertness and resistance. PVDF is obtained through the polymerization of the vinylidene fluoride monomer. PVDF thermoplastic is fabricated into sheets and pipes for engineering uses as well as powders and coatings that can be dissolved in solvents and applied across a product surface. PVDF is widely used in the chemical industry as piping for aggressive chemicals and high purity liquids. The PVDF material is used in construction, transportation, chemical processes, electricity, batteries, waste water and treatment.


title: Thermoplastic

text: Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene is commonly recognized under the brand name Teflon. PTFE is hydrophobic: aqueous liquids do not wet the material, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. This also supports its use in coatings of cooking ware. The polymer has one of the lowest coefficients of friction of any solid and is therefore commonly used for bearings and support of moving mechanical parts.


title: Bivalvia

text: Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.


title: Bivalvia

text: The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. These are joined together along one edge (the hinge line) by a flexible ligament that, usually in conjunction with interlocking "teeth" on each of the valves, forms the hinge. This arrangement allows the shell to be opened and closed without the two halves detaching. The shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes of bivalves vary from fractions of a millimetre to over a metre in length, but the majority of species do not exceed 10 cm (4 in).


title: Bivalvia

text: Bivalves have long been a part of the diet of coastal and riparian human populations. Oysters were cultured in ponds by the Romans, and mariculture has more recently become an important source of bivalves for food. Modern knowledge of molluscan reproductive cycles has led to the development of hatcheries and new culture techniques. A better understanding of the potential hazards of eating raw or undercooked shellfish has led to improved storage and processing. Pearl oysters (the common name of two very different families in salt water and fresh water) are the most common source of natural pearls. The shells of bivalves are used in craftwork, and the manufacture of jewellery and buttons. Bivalves have also been used in the biocontrol of pollution.


title: Bivalvia

text: Bivalves appear in the fossil record first in the early Cambrian more than 500 million years ago. The total number of known living species is about 9,200. These species are placed within 1,260 genera and 106 families. Marine bivalves (including brackish water and estuarine species) represent about 8,000 species, combined in four subclasses and 99 families with 1,100 genera. The largest recent marine families are the Veneridae, with more than 680 species and the Tellinidae and Lucinidae, each with over 500 species. The freshwater bivalves include seven families, the largest of which are the Unionidae, with about 700 species.


title: Bivalvia

text: The taxonomic term Bivalvia was first used by Linnaeus in the 10th edition of his "Systema Naturae" in 1758 to refer to animals having shells composed of two valves. More recently, the class was known as Pelecypoda, meaning "axe-foot" (based on the shape of the foot of the animal when extended).


title: Bivalvia

text: The name "bivalve" is derived from the Latin "bis", meaning "two", and "valvae", meaning "leaves of a door". ("Leaf" is an older word for the main, movable part of a door. We normally consider this the door itself.) Paired shells have evolved independently several times among animals that are not bivalves; other animals with paired valves include certain gastropods (small sea snails in the family Juliidae), members of the phylum Brachiopoda and the minute crustaceans known as ostracods and conchostrachans.


title: Bivalvia

text: Bivalves have bilaterally symmetrical and laterally flattened bodies, with a blade-shaped foot, vestigial head and no radula. At the dorsal or back region of the shell is the hinge point or line, which contain the umbo and beak and the lower, curved margin is the ventral or back region. The anterior or front of the shell is where the byssus (when present) and foot are located, and the posterior of the shell is where the siphons are located. With the hinge uppermost and with the anterior edge of the animal towards the viewer's left, the valve facing the viewer is the left valve and the opposing valve the right.


title: Bivalvia

text: The shell is composed of two calcareous valves held together by a ligament. The valves are made of either calcite, as is the case in oysters, or both calcite and aragonite. Sometimes, the aragonite forms an inner, nacreous layer, as is the case in the order Pteriida. In other taxa, alternate layers of calcite and aragonite are laid down. The ligament and byssus, if calcified, are composed of aragonite. The outermost layer of the shell is the periostracum, a thin layer composed of horny conchiolin. The periostracum is secreted by the outer mantle and is easily abraded. The outer surface of the valves is often sculpted, with clams often having concentric striations, scallops having radial ribs and oysters a latticework of irregular markings.


title: Bivalvia

text: In all molluscs, the mantle forms a thin membrane that covers the animal's body and extends out from it in flaps or lobes. In bivalves, the mantle lobes secrete the valves, and the mantle crest secretes the whole hinge mechanism consisting of ligament, byssus threads (where present), and teeth. The posterior mantle edge may have two elongated extensions known as siphons, through one of which water is inhaled, and the other expelled. The siphons retract into a cavity, known as the pallial sinus.


title: Bivalvia

text: The shell grows larger when more material is secreted by the mantle edge, and the valves themselves thicken as more material is secreted from the general mantle surface. Calcareous matter comes from both its diet and the surrounding seawater. Concentric rings on the exterior of a valve are commonly used to age bivalves. For some groups, a more precise method for determining the age of a shell is by cutting a cross section through it and examining the incremental growth bands.


title: Bivalvia

text: The shipworms, in the family Teredinidae have greatly elongated bodies, but their shell valves are much reduced and restricted to the anterior end of the body, where they function as scraping organs that permit the animal to dig tunnels through wood.


title: Bivalvia

text: The main muscular system in bivalves is the posterior and anterior adductor muscles. These muscles connect the two valves and contract to close the shell. The valves are also joined dorsally by the hinge ligament, which is an extension of the periostracum. The ligament is responsible for opening the shell, and works against the adductor muscles when the animal opens and closes. Retractor muscles connect the mantle to the edge of the shell, along a line known as the pallial line. These muscles pull the mantle though the valves.


title: Bivalvia

text: In sedentary or recumbent bivalves that lie on one valve, such as the oysters and scallops, the anterior adductor muscle has been lost and the posterior muscle is positioned centrally. In species that can swim by flapping their valves, a single, central adductor muscle occurs. These muscles are composed of two types of muscle fibres, striated muscle bundles for fast actions and smooth muscle bundles for maintaining a steady pull. Paired pedal protractor and retractor muscles operate the animal's foot.


title: Bivalvia

text: The sedentary habits of the bivalves have meant that in general the nervous system is less complex than in most other molluscs. The animals have no brain; the nervous system consists of a nerve network and a series of paired ganglia. In all but the most primitive bivalves, two cerebropleural ganglia are on either side of the oesophagus. The cerebral ganglia control the sensory organs, while the pleural ganglia supply nerves to the mantle cavity. The pedal ganglia, which control the foot, are at its base, and the visceral ganglia, which can be quite large in swimming bivalves, are under the posterior adductor muscle. These ganglia are both connected to the cerebropleural ganglia by nerve fibres. Bivalves with long siphons may also have siphonal ganglia to control them.


title: Bivalvia

text: The sensory organs of bivalves are largely located on the posterior mantle margins. The organs are usually mechanoreceptors or chemoreceptors, in some cases located on short tentacles. The osphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity. Statocysts within the organism help the bivalve to sense and correct its orientation. In the order Anomalodesmata, the inhalant siphon is surrounded by vibration-sensitive tentacles for detecting prey. Many bivalves have no eyes, but a few members of the Arcoidea, Limopsoidea, Mytiloidea, Anomioidea, Ostreoidea, and Limoidea have simple eyes on the margin of the mantle. These consist of a pit of photosensory cells and a lens. Scallops have more complex eyes with a lens, a two-layered retina, and a concave mirror. All bivalves have light-sensitive cells that can detect a shadow falling over the animal.


title: Bivalvia

text: Bivalves have an open circulatory system that bathes the organs in blood (hemolymph). The heart has three chambers: two auricles receiving blood from the gills, and a single ventricle. The ventricle is muscular and pumps hemolymph into the aorta, and then to the rest of the body. Some bivalves have a single aorta, but most also have a second, usually smaller, aorta serving the hind parts of the animal. The hemolymph usually lacks any respiratory pigment. In the carnivorous genus "Poromya", the hemolymph has red amoebocytes containing a haemoglobin pigment.


title: Bivalvia

text: The paired gills are located posteriorly and consist of hollow tube-like filaments with thin walls for gas exchange. The respiratory demands of bivalves are low, due to their relative inactivity. Some freshwater species, when exposed to the air, can gape the shell slightly and gas exchange can take place. Oysters, including the Pacific oyster ("Magallana gigas"), are recognized as having varying metabolic responses to environmental stress, with changes in respiration rate being frequently observed.


title: Bivalvia

text: Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. protobranchs feed in a different way, scraping detritus from the seabed, and this may be the original mode of feeding used by all bivalves before the gills became adapted for filter feeding. These primitive bivalves hold on to the bottom with a pair of tentacles at the edge of the mouth, each of which has a single palp, or flap. The tentacles are covered in mucus, which traps the food, and cilia, which transport the particles back to the palps. These then sort the particles, rejecting those that are unsuitable or too large to digest, and conveying others to the mouth.


title: Bivalvia

text: In more advanced bivalves, water is drawn into the shell from the posterior ventral surface of the animal, passes upwards through the gills, and doubles back to be expelled just above the intake. There may be two elongated, retractable siphons reaching up to the seabed, one each for the inhalant and exhalant streams of water. The gills of filter-feeding bivalves are known as ctenidia and have become highly modified to increase their ability to capture food. For example, the cilia on the gills, which originally served to remove unwanted sediment, have become adapted to capture food particles, and transport them in a steady stream of mucus to the mouth. The filaments of the gills are also much longer than those in more primitive bivalves, and are folded over to create a groove through which food can be transported. The structure of the gills varies considerably, and can serve as a useful means for classifying bivalves into groups.


title: Bivalvia

text: A few bivalves, such as the granular poromya ("Poromya granulata"), are carnivorous, eating much larger prey than the tiny microalgae consumed by other bivalves. Muscles draw water in through the inhalant siphon which is modified into a cowl-shaped organ, sucking in prey. The siphon can be retracted quickly and inverted, bringing the prey within reach of the mouth. The gut is modified so that large food particles can be digested.


title: Bivalvia

text: The unusual genus, "Entovalva", is endosymbiotic, being found only in the oesophagus of sea cucumbers. It has mantle folds that completely surround its small valves. When the sea cucumber sucks in sediment, the bivalve allows the water to pass over its gills and extracts fine organic particles. To prevent itself from being swept away, it attaches itself with byssal threads to the host's throat. The sea cucumber is unharmed.


title: Bivalvia

text: The digestive tract of typical bivalves consists of an oesophagus, stomach, and intestine. Protobranch stomachs have a mere sac attached to them while filter-feeding bivalves have elongated rod of solidified mucus referred to as the "crystalline style" projected into the stomach from an associated sac. Cilia in the sac cause the style to rotate, winding in a stream of food-containing mucus from the mouth, and churning the stomach contents. This constant motion propels food particles into a sorting region at the rear of the stomach, which distributes smaller particles into the digestive glands, and heavier particles into the intestine. Waste material is consolidated in the rectum and voided as pellets into the exhalent water stream through an anal pore. Feeding and digestion are synchronized with diurnal and tidal cycles.


title: Bivalvia

text: Carnivorous bivalves generally have reduced crystalline styles and the stomach has thick, muscular walls, extensive cuticular linings and diminished sorting areas and gastric chamber sections.


title: Bivalvia

text: The excretory organs of bivalves are a pair of nephridia. Each of these consists of a long, looped, glandular tube, which opens into the pericardium, and a bladder to store urine. They also have pericardial glands either line the auricles of the heart or attach to the pericardium, and serve as extra filtration organs. Metabolic waste is voided from the bladders through a nephridiopore near the front of the upper part of the mantle cavity and excreted.


title: Bivalvia

text: The sexes are usually separate in bivalves but some hermaphroditism is known. The gonads and either open into the nephridia, or through a separate pore into a chamber over the gills. The ripe gonads of males and females release sperm and eggs into the water column. Spawning may take place continually or be triggered by environmental factors such as day length, water temperature, or the presence of sperm in the water. Some species are "dribble spawners", releasing gametes during protracted period that can extend for weeks. Others are mass spawners and release their gametes in batches or all at once.


title: Bivalvia

text: Fertilization is usually external. Typically, a short stage lasts a few hours or days before the eggs hatch into trochophore larvae. These later develop into veliger larvae which settle on the seabed and undergo metamorphosis into adults. In some species, such as those in the genus "Lasaea", females draw water containing sperm in through their inhalant siphons and fertilization takes place inside the female. These species then brood the young inside their mantle cavity, eventually releasing them into the water column as veliger larvae or as crawl-away juveniles.


title: Bivalvia

text: Most of the bivalve larvae that hatch from eggs in the water column feed on diatoms or other phytoplankton. In temperate regions, about 25% of species are lecithotrophic, depending on nutrients stored in the yolk of the egg where the main energy source is lipids. The longer the period is before the larva first feeds, the larger the egg and yolk need to be. The reproductive cost of producing these energy-rich eggs is high and they are usually smaller in number. For example, the Baltic tellin ("Macoma balthica") produces few, high-energy eggs. The larvae hatching out of these rely on the energy reserves and do not feed. After about four days, they become D-stage larvae, when they first develop hinged, D-shaped valves. These larvae have a relatively small dispersal potential before settling out. The common mussel ("Mytilus edulis") produces 10 times as many eggs that hatch into larvae and soon need to feed to survive and grow. They can disperse more widely as they remain planktonic for a much longer time.


title: Bivalvia

text: Freshwater bivalves have different lifecycle. Sperm is drawn into a female's gills with the inhalant water and internal fertilization takes place. The eggs hatch into glochidia larvae that develop within the female's shell. Later they are released and attach themselves parasitically to the gills or fins of a fish host. After several weeks they drop off their host, undergo metamorphosis and develop into adults on the substrate.


title: Bivalvia

text: Some of the species in the freshwater mussel family, Unionidae, commonly known as pocketbook mussels, have evolved an unusual reproductive strategy. The female's mantle protrudes from the shell and develops into an imitation small fish, complete with fish-like markings and false eyes. This decoy moves in the current and attracts the attention of real fish. Some fish see the decoy as prey, while others see a conspecific. They approach for a closer look and the mussel releases huge numbers of larvae from its gills, dousing the inquisitive fish with its tiny, parasitic young. These glochidia larvae are drawn into the fish's gills, where they attach and trigger a tissue response that forms a small cyst around each larva. The larvae then feed by breaking down and digesting the tissue of the fish within the cysts. After a few weeks they release themselves from the cysts and fall to the stream bed as juvenile molluscs.


title: Bivalvia

text: Brachiopods are shelled marine organisms that superficially resembled bivalves in that they are of similar size and have a hinged shell in two parts. However, brachiopods evolved from a very different ancestral line, and the resemblance to bivalves only arose because they occupy similar ecological niches. The differences between the two groups are due to their separate ancestral origins. Different initial structures have been adapted to solve the same problems, a case of convergent evolution. In modern times, brachiopods are not as common as bivalves.


title: Bivalvia

text: Both groups have a shell consisting of two valves, but the organization of the shell is quite different in the two groups. In brachiopods, the two valves are positioned on the dorsal and ventral surfaces of the body, while in bivalves, the valves are on the left and right sides of the body, and are, in most cases, mirror images of one other. Brachiopods have a lophophore, a coiled, rigid cartilaginous internal apparatus adapted for filter feeding, a feature shared with two other major groups of marine invertebrates, the bryozoans and the phoronids. Some brachiopod shells are made of calcium phosphate but most are calcium carbonate in the form of the biomineral calcite, whereas bivalve shells are always composed entirely of calcium carbonate, often in the form of the biomineral aragonite.


title: Bivalvia

text: The Cambrian explosion took place around 540 to 520 million years ago (Mya). In this geologically brief period, all the major animal phyla diverged and these included the first creatures with mineralized skeletons. Brachiopods and bivalves made their appearance at this time, and left their fossilized remains behind in the rocks.


title: Bivalvia

text: Possible early bivalves include "Pojetaia" and "Fordilla"; these probably lie in the stem rather than crown group. "Watsonella" and "Anabarella" are perceived to be (earlier) close relatives of these taxa. Only five genera of supposed Cambrian "bivalves" exist, the others being "Tuarangia", "Camya" and "Arhouriella" and potentially "Buluniella".


title: Bivalvia

text: Bivalve fossils can be formed when the sediment in which the shells are buried hardens into rock. Often, the impression made by the valves remains as the fossil rather than the valves. During the Early Ordovician, a great increase in the diversity of bivalve species occurred, and the dysodont, heterodont, and taxodont dentitions evolved. By the Early Silurian, the gills were becoming adapted for filter feeding, and during the Devonian and Carboniferous periods, siphons first appeared, which, with the newly developed muscular foot, allowed the animals to bury themselves deep in the sediment.


title: Bivalvia

text: By the middle of the Paleozoic, around 400 Mya, the brachiopods were among the most abundant filter feeders in the ocean, and over 12,000 fossil species are recognized. By the Permian–Triassic extinction event 250 Mya, bivalves were undergoing a huge radiation of diversity. The bivalves were hard hit by this event, but re-established themselves and thrived during the Triassic period that followed. In contrast, the brachiopods lost 95% of their species diversity. The ability of some bivalves to burrow and thus avoid predators may have been a major factor in their success. Other new adaptations within various families allowed species to occupy previously unused evolutionary niches. These included increasing relative buoyancy in soft sediments by developing spines on the shell, gaining the ability to swim, and in a few cases, adopting predatory habits.


title: Bivalvia

text: For a long time, bivalves were thought to be better adapted to aquatic life than brachiopods were, outcompeting and relegating them to minor niches in later ages. These two taxa appeared in textbooks as an example of replacement by competition. Evidence given for this included the fact that bivalves needed less food to subsist because of their energetically efficient ligament-muscle system for opening and closing valves. All this has been broadly disproven, though; rather, the prominence of modern bivalves over brachiopods seems due to chance disparities in their response to extinction events.


title: Bivalvia

text: The adult maximum size of living species of bivalve ranges from in "Condylonucula maya", a nut clam, to a length of in "Kuphus polythalamia", an elongated, burrowing shipworm. However, the species generally regarded as the largest living bivalve is the giant clam "Tridacna gigas", which can grow to a length of and a weight of more than 200 kg (441 lb). The largest known extinct bivalve is a species of "Platyceramus" whose fossils measure up to in length.


title: Bivalvia

text: In his 2010 treatise, "Compendium of Bivalves", Markus Huber gives the total number of living bivalve species as about 9,200 combined in 106 families. Huber states that the number of 20,000 living species, often encountered in literature, could not be verified and presents the following table to illustrate the known diversity:


title: Bivalvia

text: The bivalves are a highly successful class of invertebrates found in aquatic habitats throughout the world. Most are infaunal and live buried in sediment on the seabed, or in the sediment in freshwater habitats. A large number of bivalve species are found in the intertidal and sublittoral zones of the oceans. A sandy sea beach may superficially appear to be devoid of life, but often a very large number of bivalves and other invertebrates are living beneath the surface of the sand. On a large beach in South Wales, careful sampling produced an estimate of 1.44 million cockles ("Cerastoderma edule") per acre of beach.


title: Bivalvia

text: Bivalves inhabit the tropics, as well as temperate and boreal waters. A number of species can survive and even flourish in extreme conditions. They are abundant in the Arctic, about 140 species being known from that zone. The Antarctic scallop, "Adamussium colbecki", lives under the sea ice at the other end of the globe, where the subzero temperatures mean that growth rates are very slow. The giant mussel, "Bathymodiolus thermophilus", and the giant white clam, "Calyptogena magnifica", both live clustered around hydrothermal vents at abyssal depths in the Pacific Ocean. They have chemosymbiotic bacteria in their gills that oxidise hydrogen sulphide, and the molluscs absorb nutrients synthesized by these bacteria. The saddle oyster, "Enigmonia aenigmatica", is a marine species that could be considered amphibious. It lives above the high tide mark in the tropical Indo-Pacific on the underside of mangrove leaves, on mangrove branches, and on sea walls in the splash zone.


title: Bivalvia

text: Some freshwater bivalves have very restricted ranges. For example, the Ouachita creekshell mussel, "Villosa arkansasensis", is known only from the streams of the Ouachita Mountains in Arkansas and Oklahoma, and like several other freshwater mussel species from the southeastern US, it is in danger of extinction. In contrast, a few species of freshwater bivalves, including the golden mussel ("Limnoperna fortunei"), are dramatically increasing their ranges. The golden mussel has spread from Southeast Asia to Argentina, where it has become an invasive species. Another well-travelled freshwater bivalve, the zebra mussel ("Dreissena polymorpha") originated in southeastern Russia, and has been accidentally introduced to inland waterways in North America and Europe, where the species damages water installations and disrupts local ecosystems.


title: Bivalvia

text: Most bivalves adopt a sedentary or even sessile lifestyle, often spending their whole lives in the area in which they first settled as juveniles. The majority of bivalves are infaunal, living under the seabed, buried in soft substrates such as sand, silt, mud, gravel, or coral fragments. Many of these live in the intertidal zone where the sediment remains damp even when the tide is out. When buried in the sediment, burrowing bivalves are protected from the pounding of waves, desiccation, and overheating during low tide, and variations in salinity caused by rainwater. They are also out of the reach of many predators. Their general strategy is to extend their siphons to the surface for feeding and respiration during high tide, but to descend to greater depths or keep their shell tightly shut when the tide goes out. They use their muscular foot to dig into the substrate. To do this, the animal relaxes its adductor muscles and opens its shell wide to anchor itself in position while it extends its foot downwards into the substrate. Then it dilates the tip of its foot, retracts the adductor muscles to close the shell, shortens its foot and draws itself downwards. This series of actions is repeated to dig deeper.


title: Bivalvia

text: Other bivalves, such as mussels, attach themselves to hard surfaces using tough byssus threads made of collagen and elastin proteins. Some species, including the true oysters, the jewel boxes, the jingle shells, the thorny oysters and the kitten's paws, cement themselves to stones, rock or larger dead shells. In oysters the lower valve may be almost flat while the upper valve develops layer upon layer of thin horny material reinforced with calcium carbonate. Oysters sometimes occur in dense beds in the neritic zone and, like most bivalves, are filter feeders.


title: Bivalvia

text: Bivalves filter large amounts of water to feed and breathe but they are not permanently open. They regularly shut their valves to enter a resting state, even when they are permanently submerged. In oysters, for example, their behaviour follows very strict circatidal and circadian rhythms according to the relative positions of the moon and sun. During neap tides, they exhibit much longer closing periods than during spring tides.


title: Bivalvia

text: Although many non-sessile bivalves use their muscular foot to move around, or to dig, members of the freshwater family Sphaeriidae are exceptional in that these small clams climb about quite nimbly on weeds using their long and flexible foot. The European fingernail clam ("Sphaerium corneum"), for example, climbs around on water weeds at the edges of lakes and ponds; this enables the clam to find the best position for filter feeding.


title: Bivalvia

text: The thick shell and rounded shape of bivalves make them awkward for potential predators to tackle. Nevertheless, a number of different creatures include them in their diet. Many species of demersal fish feed on them including the common carp ("Cyprinus carpio"), which is being used in the upper Mississippi River to try to control the invasive zebra mussel ("Dreissena polymorpha"). Birds such as the Eurasian oystercatcher ("Haematopus ostralegus") have specially adapted beaks which can pry open their shells. The herring gull ("Larus argentatus") sometimes drops heavy shells onto rocks in order to crack them open. Sea otters feed on a variety of bivalve species and have been observed to use stones balanced on their chests as anvils on which to crack open the shells. The Pacific walrus ("Odobenus rosmarus divergens") is one of the main predators feeding on bivalves in Arctic waters. Shellfish have formed part of the human diet since prehistoric times, a fact evidenced by the remains of mollusc shells found in ancient middens. Examinations of these deposits in Peru has provided a means of dating long past El Niño events because of the disruption these caused to bivalve shell growth. Further changes in shell development due to environmental stress has also been suggested to cause increased mortality in oysters due to reduced shell strength.


title: Bivalvia

text: Invertebrate predators include crustaceans, starfish and octopuses. Crustaceans crack the shells with their pincers and starfish use their water vascular system to force the valves apart and then insert part of their stomach between the valves to digest the bivalve's body. It has been found experimentally that both crabs and starfish preferred molluscs that are attached by byssus threads to ones that are cemented to the substrate. This was probably because they could manipulate the shells and open them more easily when they could tackle them from different angles. Octopuses either pull bivalves apart by force, or they bore a hole into the shell and insert a digestive fluid before sucking out the liquified contents. Certain carnivorous gastropod snails such as whelks (Buccinidae) and murex snails (Muricidae) feed on bivalves by boring into their shells. A dog whelk ("Nucella") drills a hole with its radula assisted by a shell-dissolving secretion. The dog whelk then inserts its extendible proboscis and sucks out the body contents of the victim, which is typically a blue mussel.


title: Bivalvia

text: Razor shells can dig themselves into the sand with great speed to escape predation. When a Pacific razor clam ("Siliqua patula") is laid on the surface of the beach it can bury itself completely in seven seconds and the Atlantic jackknife clam, "Ensis directus", can do the same within fifteen seconds. Scallops and file clams can swim by opening and closing their valves rapidly; water is ejected on either side of the hinge area and they move with the flapping valves in front. Scallops have simple eyes around the margin of the mantle and can clap their valves shut to move sharply, hinge first, to escape from danger. Cockles can use their foot to move across the seabed or leap away from threats. The foot is first extended before being contracted suddenly when it acts like a spring, projecting the animal forwards.


title: Bivalvia

text: In many bivalves that have siphons, they can be retracted back into the safety of the shell. If the siphons inadvertently get attacked by a predator, in some cases they snap off. The animal can regenerate them later, a process that starts when the cells close to the damaged site become activated and remodel the tissue back to its pre-existing form and size. On the other hand in some cases it does not snap off. If the siphon is exposed it is the key for a predatory fish to obtain the entire body. This tactic has been observed against bivalves with an infaunal lifestyle.


title: Bivalvia

text: File shells such as "Limaria fragilis" can produce a noxious secretion when stressed. It has numerous tentacles which fringe its mantle and protrude some distance from the shell when it is feeding. If attacked, it sheds tentacles in a process known as autotomy. The toxin released by this is distasteful and the detached tentacles continue to writhe which may also serve to distract potential predators.


title: Bivalvia

text: Oysters, mussels, clams, scallops and other bivalve species are grown with food materials that occur naturally in their culture environment in the sea and lagoons. One-third of the world's farmed food fish harvested in 2010 was achieved without the use of feed, through the production of bivalves and filter-feeding carps. European flat oysters ("Ostrea edulis") were first farmed by the Romans in shallow ponds and similar techniques are still in use. Seed oysters are either raised in a hatchery or harvested from the wild. Hatchery production provides some control of the broodstock but remains problematic because disease-resistant strains of this oyster have not yet been developed. Wild spats are harvested either by broadcasting empty mussel shells on the seabed or by the use of long, small-mesh nets filled with mussel shells supported on steel frames. The oyster larvae preferentially settle out on the mussel shells. Juvenile oysters are then grown on in nursery trays and are transferred to open waters when they reach in length.


title: Bivalvia

text: Many juveniles are further reared off the seabed in suspended rafts, on floating trays or cemented to ropes. Here they are largely free from bottom-dwelling predators such as starfish and crabs but more labour is required to tend them. They can be harvested by hand when they reach a suitable size. Other juveniles are laid directly on the seabed at the rate of per hectare. They grow on for about two years before being harvested by dredging. Survival rates are low at about 5%.


title: Bivalvia

text: The Pacific oyster ("Crassostrea gigas") is cultivated by similar methods but in larger volumes and in many more regions of the world. This oyster originated in Japan where it has been cultivated for many centuries. It is an estuarine species and prefers salinities of 20 to 25 parts per thousand. Breeding programmes have produced improved stock that is available from hatcheries. A single female oyster can produce 50–80 million eggs in a batch so the selection of broodstock is of great importance. The larvae are grown on in tanks of static or moving water. They are fed high quality microalgae and diatoms and grow fast. At metamorphosis the juveniles may be allowed to settle on PVC sheets or pipes, or crushed shell. In some cases, they continue their development in "upwelling culture" in large tanks of moving water rather than being allowed to settle on the bottom. They then may be transferred to transitional, nursery beds before being moved to their final rearing quarters. Culture there takes place on the bottom, in plastic trays, in mesh bags, on rafts or on long lines, either in shallow water or in the intertidal zone. The oysters are ready for harvesting in 18 to 30 months depending on the size required.


title: Bivalvia

text: Similar techniques are used in different parts of the world to cultivate other species including the Sydney rock oyster ("Saccostrea commercialis"), the northern quahog ("Mercenaria mercenaria"), the blue mussel ("Mytilus edulis"), the Mediterranean mussel ("Mytilus galloprovincialis"), the New Zealand green-lipped mussel ("Perna canaliculus"), the grooved carpet shell ("Ruditapes decussatus"), the Japanese carpet shell ("Venerupis philippinarum"), the pullet carpet shell ("Venerupis pullastra") and the Yesso scallop ("Patinopecten yessoensis").


title: Bivalvia

text: Production of bivalve molluscs by mariculture in 2010 was 12,913,199 tons, up from 8,320,724 tons in 2000. Culture of clams, cockles and ark shells more than doubled over this time period from 2,354,730 to 4,885,179 tons. Culture of mussels over the same period grew from 1,307,243 to 1,812,371 tons, of oysters from 3,610,867 to 4,488,544 tons and of scallops from 1,047,884 to 1,727,105 tons.


title: Bivalvia

text: Bivalves have been an important source of food for humans at least since Roman times and empty shells found in middens at archaeological sites are evidence of earlier consumption. Oysters, scallops, clams, ark clams, mussels and cockles are the most commonly consumed kinds of bivalve, and are eaten cooked or raw. In 1950, the year in which the Food and Agriculture Organization (FAO) started making such information available, world trade in bivalve molluscs was 1,007,419 tons. By 2010, world trade in bivalves had risen to 14,616,172 tons, up from 10,293,607 tons a decade earlier. The figures included 5,554,348 (3,152,826) tons of clams, cockles and ark shells, 1,901,314 (1,568,417) tons of mussels, 4,592,529 (3,858,911) tons of oysters and 2,567,981 (1,713,453) tons of scallops. China increased its consumption 400-fold during the period 1970 to 1997.


title: Bivalvia

text: It has been known for more than a century that consumption of raw or insufficiently cooked shellfish can be associated with infectious diseases. These are caused either by bacteria naturally present in the sea such as "Vibrio spp." or by viruses and bacteria from sewage effluent that sometimes contaminates coastal waters. As filter feeders, bivalves pass large quantities of water through their gills, filtering out the organic particles, including the microbial pathogens. These are retained in the animals' tissues and become concentrated in their liver-like digestive glands. Another possible source of contamination occurs when bivalves contain marine biotoxins as a result of ingesting numerous dinoflagellates. These microalgae are not associated with sewage but occur unpredictably as algal blooms. Large areas of a sea or lake may change colour as a result of the proliferation of millions of single-cell algae, and this condition is known as a red tide.


title: Bivalvia

text: In 1816 in France, a physician, J. P. A. Pasquier, described an outbreak of typhoid linked to the consumption of raw oysters. The first report of this kind in the United States was in Connecticut in 1894. As sewage treatment programmes became more prevalent in the late 19th century, more outbreaks took place. This may have been because sewage was released through outlets into the sea providing more food for bivalves in estuaries and coastal habitats. A causal link between the bivalves and the illness was not easy to demonstrate because the illness might come on days or even weeks after the ingestion of the contaminated shellfish. One viral pathogen is the "Norwalk" virus. This is resistant to treatment with chlorine-containing chemicals and may be present in the marine environment even when coliform bacteria have been killed by the treatment of sewage.


title: Bivalvia

text: Since the 1970s, outbreaks of oyster-vectored diseases have occurs throughout the world. The mortality rate of one disease causing bacteria "Vibrio vulnificus", was high at 50%. In 1978, an oyster-associated gastrointestinal infection affecting more than 2,000 people occurred in Australia. The causative agent was found to be the "Norwalk" virus and the epidemic caused major economic difficulties to the oyster farming industry in the country. In 1988, an outbreak of hepatitis A associated with the consumption of inadequately cooked clams ("Anadara subcrenata") took place in the Shanghai area of China. An estimated 290,000 people were infected and there were 47 deaths. In the United States and the European Union, since the early 1990s regulations have been in place that are designed to prevent shellfish from contaminated waters entering restaurants.


title: Bivalvia

text: Paralytic shellfish poisoning (PSP) is primarily caused by the consumption of bivalves that have accumulated toxins by feeding on toxic dinoflagellates, single-celled protists found naturally in the sea and inland waters. Saxitoxin is the most virulent of these. In mild cases, PSP causes tingling, numbness, sickness and diarrhoea. In more severe cases, the muscles of the chest wall may be affected leading to paralysis and even death. In 1937, researchers in California established the connection between blooms of these phytoplankton and PSP. The biotoxin remains potent even when the shellfish are well-cooked. In the United States, there is a regulatory limit of 80 µg/g of saxitoxin equivalent in shellfish meat.


title: Bivalvia

text: Amnesic shellfish poisoning (ASP) was first reported in eastern Canada in 1987. It is caused by the substance domoic acid found in certain diatoms of the genus "Pseudo-nitzschia". Bivalves can become toxic when they filter these microalgae out of the water. Domoic acid is a low-molecular weight amino acid that is able to destroy brain cells causing memory loss, gastroenteritis, long-term neurological problems or death. In an outbreak in the western United States in 1993, finfish were also implicated as vectors, and seabirds and mammals suffered neurological symptoms. In the United States and Canada, a regulatory limit of 20 µg/g of domoic acid in shellfish meat is set.


title: Bivalvia

text: Ecosystem services provided by marine bivalves in relation to nutrient extraction from the coastal environment have gained increased attention to mitigate adverse effects of excess nutrient loading from human activities, such as agriculture and sewage discharge. These activities damage coastal ecosystems and require action from local, regional, and national environmental management. Marine bivalves filter particles like phytoplankton, thereby transforming particulate organic matter into bivalve tissue or larger faecal pellets that are transferred to the benthos. Nutrient extraction from the coastal environment takes place through two different pathways: (i) harvest/removal of the bivalves – thereby returning nutrients back to land; or (ii) through increased denitrification in proximity to dense bivalve aggregations, leading to loss of nitrogen to the atmosphere. Active use of marine bivalves for nutrient extraction may include a number of secondary effects on the ecosystem, such as filtration of particulate material. This leads to partial transformation of particulate-bound nutrients into dissolved nutrients via bivalve excretion or enhanced mineralization of faecal material.


title: Bivalvia

text: When they live in polluted waters, bivalve molluscs have a tendency to accumulate substances such as heavy metals and persistent organic pollutants in their tissues. This is because they ingest the chemicals as they feed but their enzyme systems are not capable of metabolising them and as a result, the levels build up. This may be a health hazard for the molluscs themselves, and is one for humans who eat them. It also has certain advantages in that bivalves can be used in monitoring the presence and quantity of pollutants in their environment.


title: Bivalvia

text: There are limitations to the use of bivalves as bioindicators. The level of pollutants found in the tissues varies with species, age, size, time of year and other factors. The quantities of pollutants in the water may vary and the molluscs may reflect past rather than present values. In a study near Vladivostok it was found that the level of pollutants in the bivalve tissues did not always reflect the high levels in the surrounding sediment in such places as harbours. The reason for this was thought to be that the bivalves in these locations did not need to filter so much water as elsewhere because of the water's high nutritional content.


title: Bivalvia

text: A study of nine different bivalves with widespread distributions in tropical marine waters concluded that the mussel, "Trichomya hirsuta", most nearly reflected in its tissues the level of heavy metals (Pb, Cd, Cu, Zn, Co, Ni, and Ag) in its environment. In this species there was a linear relationship between the sedimentary levels and the tissue concentration of all the metals except zinc. In the Persian Gulf, the Atlantic pearl-oyster ("Pinctada radiata") is considered to be a useful bioindicator of heavy metals.


title: Bivalvia

text: Crushed shells, available as a by-product of the seafood canning industry, can be used to remove pollutants from water. It has been found that, as long as the water is maintained at an alkaline pH, crushed shells will remove cadmium, lead and other heavy metals from contaminated waters by swapping the calcium in their constituent aragonite for the heavy metal, and retaining these pollutants in a solid form. The rock oyster ("Saccostrea cucullata") has been shown to reduce the levels of copper and cadmium in contaminated waters in the Persian Gulf. The live animals acted as biofilters, selectively removing these metals, and the dead shells also had the ability to reduce their concentration.


title: Bivalvia

text: Conchology is the scientific study of mollusc shells, but the term conchologist is also sometimes used to describe a collector of shells. Many people pick up shells on the beach or purchase them and display them in their homes. There are many private and public collections of mollusc shells, but the largest one in the world is at the Smithsonian Institution, which houses in excess of 20 million specimens.


title: Bivalvia

text: Shells are used decoratively in many ways. They can be pressed into concrete or plaster to make decorative paths, steps or walls and can be used to embellish picture frames, mirrors or other craft items. They can be stacked up and glued together to make ornaments. They can be pierced and threaded onto necklaces or made into other forms of jewellery. Shells have had various uses in the past as body decorations, utensils, scrapers and cutting implements. Carefully cut and shaped shell tools dating back 32,000 years have been found in a cave in Indonesia. In this region, shell technology may have been developed in preference to the use of stone or bone implements, perhaps because of the scarcity of suitable rock materials.


title: Bivalvia

text: The indigenous peoples of the Americas living near the east coast used pieces of shell as wampum. The channeled whelk ("Busycotypus canaliculatus") and the quahog ("Mercenaria mercenaria") were used to make white and purple traditional patterns. The shells were cut, rolled, polished and drilled before being strung together and woven into belts. These were used for personal, social and ceremonial purposes and also, at a later date, for currency. The Winnebago Tribe from Wisconsin had numerous uses for freshwater mussels including using them as spoons, cups, ladles and utensils. They notched them to provide knives, graters and saws. They carved them into fish hooks and lures. They incorporated powdered shell into clay to temper their pottery vessels. They used them as scrapers for removing flesh from hides and for separating the scalps of their victims. They used shells as scoops for gouging out fired logs when building canoes and they drilled holes in them and fitted wooden handles for tilling the ground.


title: Bivalvia

text: Buttons have traditionally been made from a variety of freshwater and marine shells. At first they were used decoratively rather than as fasteners and the earliest known example dates back five thousand years and was found at Mohenjo-daro in the Indus Valley.


title: Bivalvia

text: Sea silk is a fine fabric woven from the byssus threads of bivalves, particularly the pen shell ("Pinna nobilis"). It used to be produced in the Mediterranean region where these shells are endemic. It was an expensive fabric and overfishing has much reduced populations of the pen shell.


title: Bivalvia

text: Crushed shells are added as a calcareous supplement to the diet of laying poultry. Oyster shell and cockle shell are often used for this purpose and are obtained as a by-product from other industries.


title: Bivalvia

text: Mother-of-pearl or nacre is the naturally occurring lustrous layer that lines some mollusc shells. It is used to make pearl buttons and in artisan craftwork to make organic jewellery. It has traditionally been inlaid into furniture and boxes, particularly in China. It has been used to decorate musical instruments, watches, pistols, fans and other products. The import and export of goods made with nacre are controlled in many countries under the International Convention of Trade in Endangered Species of Wild Fauna and Flora.


title: Bivalvia

text: A pearl is created in the mantle of a mollusk when an irritant particle is surrounded by layers of nacre. Although most bivalves can create pearls, oysters in the family Pteriidae and freshwater mussels in the families Unionidae and Margaritiferidae are the main source of commercially available pearls because the calcareous concretions produced by most other species have no lustre. Finding pearls inside oysters is a very chancy business as hundreds of shells may need to be pried open before a single pearl can be found. Most pearls are now obtained from cultured shells where an irritant substance has been purposefully introduced to induce the formation of a pearl. A "mabe" (irregular) pearl can be grown by the insertion of an implant, usually made of plastic, under a flap of the mantle and next to the mother-of-pearl interior of the shell. A more difficult procedure is the grafting of a piece of oyster mantle into the gonad of an adult specimen together with the insertion of a shell bead nucleus. This produces a superior, spherical pearl. The animal can be opened to extract the pearl after about two years and reseeded so that it produces another pearl. Pearl oyster farming and pearl culture is an important industry in Japan and many other countries bordering the Indian and Pacific Oceans.


title: Bivalvia

text: The scallop is the symbol of St James and is called "Coquille Saint-Jacques" in French. It is an emblem carried by pilgrims on their way to the shrine of Santiago de Compostela in Galicia. The shell became associated with the pilgrimage and came to be used as a symbol showing hostelries along the route and later as a sign of hospitality, food and lodging elsewhere.


title: Bivalvia

text: Roman myth has it that Venus, the goddess of love, was born in the sea and emerged accompanied by fish and dolphins, with Botticelli depicting her as arriving in a scallop shell. The Romans revered her and erected shrines in her honour in their gardens, praying to her to provide water and verdant growth. From this, the scallop and other bivalve shells came to be used as a symbol for fertility. Its depiction is used in architecture, furniture and fabric design and it is the logo of Royal Dutch Shell, the global oil and gas company.


title: Bivalvia

text: For the past two centuries no consensus has existed on bivalve phylogeny from the many classifications developed. In earlier taxonomic systems, experts used a single characteristic feature for their classifications, choosing among shell morphology, hinge type or gill type. Conflicting naming schemes proliferated due to these taxonomies based on single organ systems. One of the most widely accepted systems was that put forward by Norman D. Newell in Part N of the "Treatise on Invertebrate Paleontology", which employed a classification system based on general shell shape, microstructures and hinge configuration. Because features such as hinge morphology, dentition, mineralogy, shell morphology and shell composition change slowly over time, these characteristics can be used to define major taxonomic groups.


title: Bivalvia

text: Since the year 2000, taxonomic studies using cladistical analyses of multiple organ systems, shell morphology (including fossil species) and modern molecular phylogenetics have resulted in the drawing up of what experts believe is a more accurate phylogeny of the Bivalvia. Based upon these studies, a new proposed classification system for the Bivalvia was published in 2010 by Bieler, Carter & Coan. In 2012, this new system was adopted by the World Register of Marine Species (WoRMS) for the classification of the Bivalvia. Some experts still maintain that Anomalodesmacea should be considered a separate subclass, whereas the new system treats it as the order Anomalodesmata, within the subclass Heterodonta. Molecular phylogenetic work continues, further clarifying which Bivalvia are most closely related and thus refining the classification.


title: Bivalvia

text: R.C. Moore, in Moore, Lalicker, and Fischer, 1952, "Invertebrate Fossils", gives a practical and useful classification of pelecypods (Bivalvia) even if somewhat antiquated, based on shell structure, gill type, and hinge teeth configuration. Subclasses and orders given are:


title: Bivalvia

text: Prionodesmacea have a prismatic and nacreous shell structure, separated mantle lobes, poorly developed siphons, and hinge teeth that are lacking or unspecialized. Gills range from protobranch to eulamellibranch. Teleodesmacea on the other hand have a porcelanous and partly nacreous shell structure; Mantle lobes that are generally connected, well developed siphons, and specialized hinge teeth. In most, gills are eulamellibranch.


title: Bivalvia

text: In his 1935 work "Handbuch der systematischen Weichtierkunde" (Handbook of Systematic Malacology), Johannes Thiele introduced a mollusc taxonomy based upon the 1909 work by Cossmann and Peyrot. Thiele's system divided the bivalves into three orders. "Taxodonta" consisted of forms that had taxodont dentition, with a series of small parallel teeth perpendicular to the hinge line. "Anisomyaria" consisted of forms that had either a single adductor muscle or one adductor muscle much smaller than the other. "Eulamellibranchiata" consisted of forms with ctenidial gills. The Eulamellibranchiata was further divided into four suborders: "Schizodonta", "Heterodonta", "Adapedonta" and "Anomalodesmata".


title: Bivalvia

text: The systematic layout presented here follows Newell's 1965 classification based on hinge tooth morphology (all taxa marked † are extinct) :


title: Bivalvia

text: The monophyly of the subclass Anomalodesmata is disputed. The standard view now is that it resides within the subclass Heterodonta.


title: Bivalvia

text: An alternative systematic scheme exists using gill morphology. This distinguishes between Protobranchia, Filibranchia and Eulamellibranchia. The first corresponds to Newell's Palaeotaxodonta and Cryptodonta, the second to his Pteriomorphia, with the last corresponding to all other groups. In addition, Franc separated the Septibranchia from his eulamellibranchs because of the morphological differences between them. The septibranchs belong to the superfamily Poromyoidea and are carnivorous, having a muscular septum instead of filamentous gills.


title: Bivalvia

text: In May 2010, a new taxonomy of the Bivalvia was published in the journal "Malacologia". In compiling this, the authors used a variety of phylogenetic information including molecular analysis, anatomical analysis, shell morphology and shell microstructure as well as bio-geographic, paleobiogeographic and stratigraphic information. In this classification 324 families are recognized as valid, 214 of which are known exclusively from fossils and 110 of which occur in the recent past, with or without a fossil record. This classification has since been adopted by WoRMS.


title: Bivalvia

text: Proposed classification of Class Bivalvia (under the redaction of Rüdiger Bieler, Joseph G. Carter and Eugene V. Coan) (all taxa marked † are extinct) :


title: HM Prison Wakefield

text: His Majesty's Prison Wakefield is a Category A men's prison in Wakefield, West Yorkshire, England, operated by His Majesty's Prison Service. The prison has been nicknamed the "Monster Mansion" due to the large number of high-profile, high-risk sex offenders and murderers held there.


title: HM Prison Wakefield

text: Wakefield Prison was originally built as a house of correction in 1594. Most of the current prison buildings date from the Victorian era. The current prison was designated a Dispersal prison in 1967, holding 144 inmates and is the oldest of the Dispersal prisons still operating across England and Wales.


title: HM Prison Wakefield

text: The English Dialect Dictionary indicates references to "Wakefield" were often short for referring to the long-standing prison (e.g. "being sent to Wakefield" meant being sent to prison).


title: HM Prison Wakefield

text: The exercise yard at Wakefield had a mulberry tree, around which inmates that were mothers used to exercise. This has been linked to the nursery rhyme "Here We Go Round the Mulberry Bush" by erstwhile prison governor RS Duncan in his 1994 book. This origin of the song is also propounded on the prison's website. There is no corroborative evidence to support this theory. The tree was removed in May 2019 as it had died. A cutting from it was taken by a retired prison officer. This will be used in an attempt to grow the tree again.


title: HM Prison Wakefield

text: During the First World War, Wakefield Prison was used as a Home Office work camp. The ordinary criminal prisoners were removed, and the new influx were sentenced to two or more years' imprisonment for refusing to obey military orders. After the closure of Dyce Work Camp in October 1916, Wakefield Prison was also used to intern conscientious objectors. In September 1918 a group of conscientious objectors took advantage of a slackening in the prison regime that occurred towards the end of the war, by rebelling and refusing to undertake any work. They issued a list of demands for better treatment, known as the Wakefield Manifesto.


title: HM Prison Wakefield

text: As a high-security prison, Wakefield was used to house IRA prisoners intermittently during the 20th century. In some cases in the 1950s, the IRA attempted to free the prisoners, such as Cathal Goulding in 1956 (the attempt was aborted when the sirens sounded) and James Andrew Mary Murphy in 1959 (who was freed). During a hunger strike by Provisional IRA prisoners, Frank Stagg died in Wakefield Prison on 12 February 1976. The case brought international media attention as the Irish Government denied Stagg's last request for a military funeral march from Dublin to Ballina, and instead arranged for the Irish police to bury him secretly. On 1 March 1976, Merlyn Rees, the Secretary of State for Northern Ireland in the Wilson ministry, announced that those people convicted of causing terrorist offences would no longer be entitled to Special Category Status, which was challenged during later hunger strikes.


title: HM Prison Wakefield

text: In 2001, it was announced that a new ultra-secure unit was to be built at Wakefield Prison. The unit was to house the most dangerous inmates within the British prisons system, and was the first such unit of its kind to be built in the United Kingdom.


title: HM Prison Wakefield

text: In March 2004, an inspection report from Her Majesty's Chief Inspector of Prisons criticised staff at Wakefield Prison for being disrespectful to inmates. The report claimed that the prison was "over-controlled", and a third of the prison's inmates claimed to have been victimised.


title: HM Prison Wakefield

text: Wakefield Prison holds approximately 600 of Britain's most dangerous people (mainly sex offenders, murderers, and prisoners serving life sentences). Accommodation at the prison comprises single-occupancy cells with integral sanitation. All residential units have kitchens available for offenders to prepare their own meals. An Incentives and Earned Privileges system allows standard and enhanced offenders the opportunity of in-cell TV. Like other HM Prisons, all offenders are subject to mandatory drugs testing and there are voluntary testing arrangements, which are compulsory for all offenders employed, for example as wing cleaners or kitchen workers.


title: HM Prison Wakefield

text: HMP Wakefield offers a range of activities for inmates, including charity work, an accredited course in industrial cleaning, and a Braille shop where offenders convert books to Braille. The Education Department is operated by The Manchester College, and offers learning opportunities ranging from basic skills to Open University courses. Other facilities include a prison shop, gym, and multi-faith chaplaincy.


title: HM Prison Wakefield

text: A prison inspection in 2018 found that Wakefield Prison was on the whole calm, secure, decent and well managed. The rest of the prison service could learn good practice from Wakefield. Despite the above, prisoners needing psychiatric care face unacceptable delays before they are transferred to secure psychiatric hospitals, and prisoners' mental condition worsens while they are waiting for transfer. Peter Clarke said, "Because of the totally unacceptable delays in doing so, many prisoners across the prison estate are held in conditions that are not in any way therapeutic and indeed in many cases clearly exacerbate their condition. (...) The situation at Wakefield was yet another example of prisoners with severe illness not receiving the care that they needed." Inspectors noted a prisoner who was "exceptionally challenging to manage and had complex needs that could not be met in the prison. While staff attempted to manage him positively and constructively, his condition was deteriorating during a lengthy wait to be admitted to a secure hospital," according to the inspection report.


title: Carl Lentz

text: Stephen Carl Lentz is an American former pastor. Carl Lentz was known as a celebrity pastor, spiritual advisor to celebrities such as Justin Bieber, Kendall Jenner, and Selena Gomez and categorized as a hype-priest by "GQ". He was the lead pastor of Hillsong NYC until November 4, 2020, when he was fired by Hillsong Global Pastor Brian Houston for "leadership issues and breaches of trust, plus a recent revelation of moral failures." On May 31, 2021, the former nanny of Lentz's children accused him of bullying, abuse of power, and sexual abuse.


title: Carl Lentz

text: Carl Lentz was born in Virginia Beach, Virginia. From 1998 to 2000, he attended North Carolina State University and was a walk-on basketball player on the school's men's basketball team. As an adult, he moved to Los Angeles to study at The King's College and Seminary. He then went on to study at Hillsong International Leadership College of Hillsong Church in Sydney, Australia. It was during his studies, at the age of 20, that he and Joel Houston, Hillsong founder Brian Houston's son, had the idea to plant a campus of Hillsong Church in New York City. He graduated in theology in 2003 and returned to Virginia Beach. He then became a youth pastor after being ordained.


title: Carl Lentz

text: In 2010, Lentz co-founded Hillsong NYC in New York City and radically changed and impacted church and ministries especially amongst the unchurched age group - millennials. Lentz even started the fashion and branding trend amongst younger pastors such as tattoos, hair style, clothing and footwear.


title: Carl Lentz

text: Lentz baptized Justin Bieber, was present at the baptism of Kevin Durant, and has befriended various other well-known people.