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Microsporidia
This article is about parasitic fungi group. For the ascomycete fungi genus, see Microsporum. For the green algae genus, see Microspora. For the beetle family, see Microsporidae.
Sporoblast of
Fibrillanosema crangonycis
(unranked): Opisthosporidia
Division: Microsporidia
Balbiani, 1882[1]
Classes and orders
See text.
Microsporidiida Labbé, 1899
Microsporea Delphy, 1936 [1963], Levine et al., 1980[2][3]
Microsporidea Corliss & Levine, 1963[4]
Microspora Sprague, 1969, 1977[5]
Microsporida Tuzet at al. 1971
Microsporidia are a group of spore-forming unicellular parasites. They were once considered protozoans or protists, but are now known to be fungi,[6] or a sister group to fungi.[7] Loosely 1500 of the probably more than one million[8] species are named now. Microsporidia are restricted to animal hosts, and all major groups of animals host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish; the named species of microsporidia usually infect one host species or a group of closely related taxa. Several species, most of which are opportunistic, also infect humans.
Approximately 10 percent of the species are parasites of vertebrates—including humans, in which they can cause microsporidiosis.
After infection they influence their hosts in various ways and all organs and tissues are invaded, though generally by different species of microsporidia; some species are lethal, and a few are used in biological control of insect pests. Parasitic castration, gigantism, or change of host sex are all potential effects of microsporidian parasitism (in insects). In the most advanced cases of parasitism the microsporidium rules the host cell completely and controls its metabolism and reproduction, forming a xenoma.[9]
Replication takes place within the host's cells, which are infected by means of unicellular spores; these vary from 1–40 μm, making them some of the smallest eukaryotes.[citation needed] Microsporidia that infect mammals are 1.0–4.0 μm.[10] They also have the smallest eukaryotic genomes.
The terms "microsporidium" (pl. "microsporidia") and "microsporidian" are used as vernacular names for members of the group. The name Microsporidium Balbiani, 1884[11] is also used as a catchall genus for incertae sedis members.[12]
Xenoma on flatfish caused by Glugea stephani
1 Morphology
2 Infection
3 Medical implications
3.1 Clinical
4 As hyperparasites
5 Genomes
6 Classification
Morphology[edit]
Dictyocoela diporeiae.[13] A, meront and spore; B, spore wall; C, polar filament
Microsporidia lack mitochondria, instead possessing mitosomes, they also lack motile structures, such as flagella.
Microsporidia produce highly resistant spores, capable of surviving outside their host for up to several years. Spore morphology is useful in distinguishing between different species. Spores of most species are oval or pyriform, but rod-shaped or spherical spores are not unusual. A few genera produce spores of unique shape for the genus.
The spore is protected by a wall, consisting of three layers:
an outer electron-dense exospore
a median, wide and seemingly structureless endospore, containing chitin
a thin internal plasma membrane
In most cases there are two closely associated nuclei, forming a diplokaryon, but sometimes there is only one.
The anterior half of the spore contains a harpoon-like apparatus with a long, thread-like polar filament, which is coiled up in the posterior half of the spore. The anterior part of the polar filament is surrounded by a polaroplast, a lamella of membranes. Behind the polar filament, there is a posterior vacuole.[9]
Infection[edit]
In the gut of the host the spore germinates, it builds up osmotic pressure until its rigid wall ruptures at its thinnest point at the apex; the posterior vacuole swells, forcing the polar filament to rapidly eject the infectious content into the cytoplasm of the potential host. Simultaneously the material of the filament is rearranged to form a tube which functions as a hypodermic needle and penetrates the gut epithelium.
Once inside the host cell, a sporoplasm grows, dividing or forming a multinucleate plasmodium, before producing new spores; the life cycle varies considerably. Some have a simple asexual life cycle,[14] while others have a complex life cycle involving multiple hosts and both asexual and sexual reproduction. Different types of spores may be produced at different stages, probably with different functions including autoinfection (transmission within a single host).
Medical implications[edit]
In animals and humans, microsporidia often cause chronic, debilitating diseases rather than lethal infections. Effects on the host include reduced longevity, fertility, weight, and general vigor. Vertical transmission of microsporidia is frequently reported. In the case of insect hosts, vertical transmission often occurs as transovarial transmission, where the microsporidian parasites pass from the ovaries of the female host into eggs and eventually multiply in the infected larvae. Amblyospora salinaria n. sp. which infects the mosquito Culex salinarius Coquillett, and Amblyospora californica which infects the mosquito Culex tarsalis Coquillett, provide typical examples of transovarial transmission of microsporidia.[15][16][17][18]
Microsporidia, specifically the mosquito-infecting Vavraia culicis, are being explored as a possible 'evolution-proof' malaria-control method.[19] Microsporidian infection of Anopheles gambiae (the principal vector of Plasmodium falciparum malaria) reduces malarial infection within the mosquito, and shortens the mosquito lifespan;[20] as the majority of malaria-infected mosquitoes naturally die before the malaria parasite is mature enough to transmit, any increase in mosquito mortality through microsporidian-infection may reduce malaria transmission to humans.
Clinical[edit]
Main article: Microsporidiosis
This section needs expansion. You can help by adding to it. (November 2013)
Microsporidian infections of humans sometimes cause a disease called microsporidiosis. At least 14 microsporidian species, spread across eight genera, have been recognized as human pathogens; these include Trachipleistophora hominis.[21]
As hyperparasites[edit]
A hyperparasitic microsporidian, Nosema podocotyloidis, a parasite of a digenean which is itself a parasite of a fish [22]
Microsporidia can infect a variety of hosts, including hosts which are themselves parasites. In that case, the microsporidian species is a hyperparasite, i.e. a parasite of a parasite. As an example, more than eighteen species are known which parasitize digeneans (parasitic flatworms); these digeneans are themselves parasites in various vertebrates and molluscs. Eight of these species belong to the genus Nosema.[22]
Genomes[edit]
Microsporidia have the smallest known (nuclear) eukaryotic genomes; the parasitic lifestyle of microsporidia has led to a loss of many mitochondrial and Golgi genes, and even their ribosomal RNAs are reduced in size compared with those of most eukaryotes. As a consequence, the genomes of microsporidia are much smaller than those of other eukaryotes. Currently known microsporidial genomes are 2.5 to 11.6 Mb in size, encoding from 1,848 to 3,266 proteins which is in the same range as many bacteria.[23]
Horizontal gene transfer (HGT) seems to have occurred many times in microsporidia. For instance, the genomes of Encephalitozoon romaleae and Trachipleistophora hominis contain genes that derive from animals and bacteria, and some even from fungi.[23]
Classification[edit]
Further information: Wikispecies:Microsporidia
The first described microsporidian genus, Nosema, was initially put by Nägeli in the fungal group Schizomycetes together with some bacteria and yeasts.[24][25] For some time microsporidia were considered as very primitive eukaryotes, placed in the protozoan group Cnidospora.[4] Later, especially because of the lack of mitochondria, they were placed along with the other Protozoa such as diplomonads, parabasalids and archamoebae in the protozoan-group Archezoa.[26] More recent research has falsified this theory of early origin (for all of these), yet microsporidia are proposed to be highly developed and specialized organisms, which just dispensed functions that are needed no longer, because they are supplied by the host.[27] Furthermore, spore-forming organisms in general do have a complex system of reproduction, both sexual and asexual, which look far from primitive.
Nowadays microsporidia are placed within the Fungi or as a sister-group of the Fungi with a common ancestor.[28][29][30][31]
Forming of clades is largely based on habitat and host. Three classes of Microsporidia are proposed by Vossbrinck and Debrunner-Vossbrinck, based on the habitat: Aquasporidia, Marinosporidia and Terresporidia.[32]
Another classification could be:[33]
Class Metchnikovellea Weiser 1977 emend. Cavalier-Smith 1993 [Manubrispora Cavalier-Smith 1998]
Order Metchnikovellida Vivier 1977
Family Amphiacanthidae
Family Metchnikovellidae Caullery & Mesnil 1897
Class Microsporea Delphy 1936 ex Levine & Corliss 1963
Family Cougourdellidae Poisson 1953
Family Facilisporidae
Family Heterovesiculidae Lange et al. 1995
Family Myosporidae
Family Nadelsporidae
Family Neonosemoidiidae
Family Ordosporidae
Family Pseudonosematidae
Family Telomyxidae Leger & Hesse 1910
Family Toxoglugeidae
Family Tubulinosematidae
Subclass Haplophasea Sprague, Becnel & Hazard 1992
Order Chytridiopsida Weiser 1974
Family Chytridiopsidae Sprague, Ormieres & Manier 1972
Family Buxtehudiidae Larsson 1980
Family Enterocytozoonidae
Family Burkeidae Sprague 1977
Family Hesseidae Ormierees & Sprague 1973
Order Glugeida Issi 1986
Family Glugeidae Thelohan 1892 [Pleistophoridae Stempell 1909]
Family Gurleyidae Sprague 1977
Family Encephalitozoonidae
Family Abelsporidae
Family Tuzetiidae Sprague, Tuzet & Maurand 1977
Family Microfilidae
Family Unikaryonidae Sprague 1977
Subclass Dihaplophasea Sprague, Becnel & Hazard 1992
Order Meiodihaplophasida Sprague, Becnel & Hazard 1992
Superfamily Thelohanioidea Hazard & Oldacre 1975
Family Thelohaniidae Hazard & Oldacre 1975 [Coccosporidae]
Family Duboscqiidae Sprague 1977
Family Janacekiidae
Family Pereziidae Loubes et al. 1977
Family Striatosporidae
Family Cylindrosporidae
Superfamily Burenelloidea Jouvenaz & Hazard 1978
Family Burenellidae Jouvenaz & Hazard 1978
Superfamily Amblyosporoidea Weiser 1977
Family Amblyosporidae Weiser 1977
Order Dissociodihaplophasida Sprague, Becnel & Hazard 1992
Superfamily Nosematoidea Labbe
Family Nosematidae Labbe 1899
Family Ichthyosporidiidae
Family Caudosporidae Weiser 1958
Family Pseudopleistophoridae Sprague 1977
Family Mrazekiidae Leger & Hesse 1922
Superfamily Culicosporoidea Weiser 1977
Family Culicosporidae Weisser 1977
Family Culicosporellidae
Family Golbergiidae
Family Spragueidae Weissenberg 1976
Superfamily Ovavesiculoidea Sprague, Becnel & Hazard 1992
Family Ovavesiculidae
Family Tetramicridae
A third classification by Cavalier-Smith 1993:[34]
Subphyla Rudimicrospora Cavalier-Smith 1993
Class Minisporea Cavalier-Smith 1993
Order Minisporida Sprague, 1972
Class Metchnikovellea Weiser, 1977
Order Metchnikovellida Vivier, 1975
Subphyla Polaroplasta Cavalier-Smith 1993
Class Pleistophoridea Cavalier-Smith 1993
Order Pleistophorida Stempell 1906
Class Disporea Cavalier-Smith 1993
Subclass Unikaryotia Cavalier-Smith 1993
Subclass Diplokaryotia Cavalier-Smith 1993
List of Microsporidian genera
Glugea, a genus of microsporidia
Nosema apis, a microsporidian parasite of bees
^ Balbiani, G. 1882. Sur les microsporidies ou psorospermies des Articulés. C. R. Acad. Sci. 95:1168–71, [1].
^ Delphy, J. 1936. Sous-règne des Protozoaires. In: Perrier, R. (ed.). La Faune de la France en tableaux synoptiques illustrés, v. 1A. Delagrave: Paris.
^ Levine, N. D. et al. (1980). A Newly Revised Classification of the Protozoa. The Journal of Protozoology 27: 37-58, [2].
^ a b Corliss JO, Levine ND (1963). "Establishment of the Microsporidea as a new class in the protozoan subphylum Cnidospora". The Journal of Protozoology. 10 (Suppl): 26–27. doi:10.1111/jeu.1963.10.issue-s3.
^ Sprague, V. (1977). Classification and phylogeny of the Microsporidia. In: Comparative pathobiology. vol. 2, Systematics of the Microsporidia. Lee A. Bulla & Thomas C. Cheng (ed.). pp. 1-30. New York: Plenum Press, [3].
^ Hibbett, D.S. et al. (2007) A higher level phylogenetic classification of the Fungi. Mycological Research 111 (5): 509–47, [4].
^ Silar, Philippe (2016). Protistes Eucaryotes : Origine, Evolution et Biologie des Microbes Eucaryotes. HAL. p. 462. ISBN 978-2-9555841-0-1.
^ Hawksworth, David (2001). "The magnitude of fungal diversity: The 1.5 million spices estimate revisited". Mycological Research. 105 (12): 1422. doi:10.1017/S0953756201004725.
^ a b Ronny Larsson, Lund University (Department of Cell and Organism Biology) Cytology and taxonomy of the microsporidia 2004.
^ Didier, ES. (Apr 2005). "Microsporidiosis: an emerging and opportunistic infection in humans and animals". Acta Trop. 94 (1): 61–76. doi:10.1016/j.actatropica.2005.01.010. PMID 15777637.
^ Balbiani, G. 1884. Les Psorospermies des Articulés ou Microsporidies, pp. 150-168, 184. In: Leçons sur les sporozoaires. Paris: Doin, [5].
^ Hoffman, G. (1999). Parasites of North American Freshwater Fishes, 2nd edn, University of California Press, Berkeley, California, USA, p. 89, [6].
^ Winters, A. D., Faisal, M. 2014. Molecular and ultrastructural characterization of Dictyocoela diporeiae n. sp. (Microsporidia), a parasite of Diporeia spp. (Amphipoda, Gammaridea). Parasite, 21, 26 doi:10.1051/parasite/2014028
^ Ironside JE (2007). "Multiple losses of sex within a single genus of Microsporidia". BMC Evolutionary Biology. 7: 48. doi:10.1186/1471-2148-7-48. PMC 1853083. PMID 17394631.
^ Andreadis TG, Hall DW; Hall (August 1979). "Development, ultrastructure, and mode of transmission of Amblyospora sp. (Microspora) in the mosquito". The Journal of Protozoology. 26 (3): 444–52. doi:10.1111/j.1550-7408.1979.tb04651.x. PMID 536933.
^ Andreadis TG, Hall DW; Hall (September 1979). "Significance of transovarial infections of Amblyospora sp. (Microspora:Thelohaniidae) in relation to parasite maintenance in the mosquito Culex salinarius". Journal of Invertebrate Pathology. 34 (2): 152–7. doi:10.1016/0022-2011(79)90095-8. PMID 536610.
^ Jahn GC, Hall DW, Zam SG (1986). "A comparison of the life cycles of two Amblyospora (Microspora: Amblyosporidae) in the mosquitoes Culex salinarius and Culex tarsalis Coquillett". Journal of the Florida Anti-Mosquito Association. 57 (1): 24–27.
^ Becnel JJ, Andreadis TG; Andreadis (May 1998). "Amblyospora salinaria n. sp. (Microsporidia: amblyosporidae), parasite of Culex salinarius (Diptera: culicidae): its life cycle stages in an intermediate host". Journal of Invertebrate Pathology. 71 (3): 258–62. doi:10.1006/jipa.1998.4729. PMID 9538031.
^ Koella, Jacob C.; Lorenz, Lena; Bargielowski, Irka (2009). Chapter 12 Microsporidians as Evolution-Proof Agents of Malaria Control?. Advances in Parasitology. 68. pp. 315–327. doi:10.1016/S0065-308X(08)00612-X. ISBN 978-0-12-374787-7. PMID 19289199. Archived from the original on 2013-02-01. Retrieved 2009-12-10.
^ Bargielowski I, Koella JC; Koella (2009). Baylis, Matthew (ed.). "A Possible Mechanism for the Suppression of Plasmodium berghei Development in the Mosquito Anopheles gambiae by the Microsporidian Vavraia culicis". PLoS ONE. 4 (3): e4676. Bibcode:2009PLoSO...4.4676B. doi:10.1371/journal.pone.0004676. PMC 2651578. PMID 19277119.
^ Heinz, E; Williams, TA; Nakjang, S; et al. (Oct 2012). "The genome of the obligate intracellular parasite Trachipleistophora hominis: New insights into microsporidian genome dynamics and reductive evolution". PLoS Pathog. 8 (10): e1002979. doi:10.1371/journal.ppat.1002979. PMC 3486916. PMID 23133373.
^ a b Toguebaye, B. S.; Quilichini, Y.; Diagne, P. M.; Marchand, B. (2014). "Ultrastructure and development of Nosema podocotyloidis n. sp. (Microsporidia), a hyperparasite of Podocotyloides magnatestis (Trematoda), a parasite of Parapristipoma octolineatum (Teleostei)". Parasite. 21: 44. doi:10.1051/parasite/2014044. PMC 4150386. PMID 25174849.
^ a b Corradi, N.; Selman, M. (2013). "Latest Progress in Microsporidian Genome Research". Journal of Eukaryotic Microbiology. 60 (3): 309–312. doi:10.1111/jeu.12030. PMID 23445243.
^ Nägeli, C. von (1857). Über die neue Krankheit der Seidenraupe und verwandte Organismen. pp. 760–61. In: Caspary, R. (ed.). Bericht über die Verhandlungen der 33. Versammlung deutscher Naturforscher und Aerzte, gehalten in Bonn von 18 bis 24 September 1857. Botanische Zeitung 15: 749–776, [7].
^ Keeling, P. J., & Fast, N. M. (2002). Microsporidia: biology and evolution of highly reduced intracellular parasites. Annual Reviews in Microbiology, 56(1), 93-116, [8].
^ Cavalier-Smith, T. (1993). Kingdom protozoa and its 18 phyla. Microbiological Reviews 57 (4): 953–994, [9].
^ Keeling PJ, Slamovits CH; Slamovits (December 2004). "Simplicity and Complexity of Microsporidian Genomes". Eukaryotic Cell. 3 (6): 1363–9. doi:10.1128/EC.3.6.1363-1369.2004. PMC 539024. PMID 15590811.
^ Fischer WM, Palmer JD; Palmer (September 2005). "Evidence from small-subunit ribosomal RNA sequences for a fungal origin of Microsporidia". Molecular Phylogenetics and Evolution. 36 (3): 606–22. doi:10.1016/j.ympev.2005.03.031. PMID 15923129.
^ Liu YJ, Hodson MC, Hall BD; Hodson; Hall (2006). "Loss of the flagellum happened only once in the fungal lineage: phylogenetic structure of Kingdom Fungi inferred from RNA polymerase II subunit genes". BMC Evolutionary Biology. 6: 74. doi:10.1186/1471-2148-6-74. PMC 1599754. PMID 17010206. CS1 maint: Multiple names: authors list (link)
^ Gill EE, Fast NM; Fast (June 2006). "Assessing the microsporidia-fungi relationship: Combined phylogenetic analysis of eight genes". Gene. 375: 103–9. doi:10.1016/j.gene.2006.02.023. PMID 16626896.
^ Lee SC, Corradi N, Byrnes EJ, et al. (November 2008). "Microsporidia evolved from ancestral sexual fungi". Current Biology. 18 (21): 1675–9. Bibcode:1996CBio....6.1213A. doi:10.1016/j.cub.2008.09.030. PMC 2654606. PMID 18976912.
^ Vossbrinck CR, Debrunner-Vossbrinck BA; Debrunner-Vossbrinck (May 2005). "Molecular phylogeny of the Microsporidia: ecological, ultrastructural and taxonomic considerations". Folia Parasitologica. 52 (1–2): 131–42, discussion 130. doi:10.14411/fp.2005.017. PMID 16004372.
^ Alimov, A. F. ed. (May 2007). "Protista 2: Handbook on zoology". Nauka: 1141. CS1 maint: Extra text: authors list (link)
^ Cavalier-Smith (1993). "Kingdom Protozoa and its 18 phyla" (PDF).
Data related to Microsporidia at Wikispecies
BioHealthBase Bioinformatics Resource Center Database of microspordia sequences and related information.
Microsporidia at the US National Library of Medicine Medical Subject Headings (MeSH)
Wikimedia Commons has media related to Microsporidia.
Opisthokont: True fungi classification, fungal orders
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(with basidia)
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Fungal phyla are underlined. See also: fungi imperfecti (polyphyletic group).
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Sources and alternative views: Wikispecies.
Wikispecies: Microsporidia
EoL: 5006395
EPPO: 1MICRP
Fossilworks: 212611
Fungorum: 99056
MycoBank: 99056
NCBI: 6029
Retrieved from "https://en.wikipedia.org/w/index.php?title=Microsporidia&oldid=890167199"
Fungus phyla
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Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates. Included in this definition are the living hagfish and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods; because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. The traditional term pisces is considered a typological, but not a phylogenetic classification; the earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era.
Many fish of the Paleozoic developed external armor. The first fish with jaws appeared in the Silurian period, after which many became formidable marine predators rather than just the prey of arthropods. Most fish are ectothermic, allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish can communicate in their underwater environments through the use of acoustic communication. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another; the production of sounds as a means of communication among fish is most used in the context of feeding, aggression or courtship behaviour. The sounds emitted by fish can vary depending on the stimulus involved, they can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.
Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams to the abyssal and hadal depths of the deepest oceans, although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates. Fish are an important resource for humans worldwide as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean, they are caught by recreational fishers, kept as pets, raised by fishkeepers, exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, as the subjects of art and movies. Fish do not represent a monophyletic group, therefore the "evolution of fish" is not studied as a single event. Early fish from the fossil record are represented by a group of small, armored fish known as ostracoderms. Jawless fish lineages are extinct.
An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils; the diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways; the first ancestors of fish may have kept the larval form into adulthood, although the reverse is the case. Fish are a paraphyletic group: that is, any clade containing all fish contains the tetrapods, which are not fish. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications. Traditional classification divides fish into three extant classes, with extinct forms sometimes classified within the tree, sometimes as their own classes: Class Agnatha Subclass Cyclostomata Subclass Ostracodermi † Class Chondrichthyes Subclass Elasmobranchii Subclass Holocephali Class Placodermi † Class Acanthodii † Class Osteichthyes Subclass Actinopterygii Subclass Sarcopterygii The above scheme is the one most encountered in non-specialist and general works.
Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini Class Pteraspidomorphi † Class Thelodonti † Class Anaspida † Class Petromyzontida or Hyperoartia Petromyzontidae Class Conodonta † Class Cephalaspidomorphi † Galeaspida † Pituriaspida † Osteostraci † Infraphylum Gnathostomata Class Placodermi † Class Chondrichthyes Class Acanthodii † Superclass Osteichthy
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
Microsporum
Microsporum is a genus of fungi that causes tinea capitis, tinea corporis and other dermatophytoses. Microsporum forms both microconidia on short conidiophores. Macroconidia are hyaline, variable in form, spindle-shaped to obovate, 7–20 by 30–160 um in size, with thin or thick echinulate to verrucose cell walls, their shape and cell wall features are important characteristics for species identification. Microconidia are hyaline, single-celled, pyriform to clavate, smooth-walled, 2.5–3.5 by 4–7 um in size and are not diagnostic for any one species. The separation of this genus from Trichophyton is based on the roughness of the macroconidial cell wall, although in practice this may sometimes be difficult to observe. Seventeen species of Microsporum have been described. Microsporum amazonicum Microsporum audouinii Microsporum boullardii Microsporum canis Microsporum canis var. distortum Microsporum cookei Microsporum distortum Microsporum duboisii Microsporum equinum Microsporum ferrugineum Microsporum fulvum Microsporum gallinae Microsporum gypseum Microsporum langeronii Microsporum nanum Microsporum persicolor Microsporum praecox Microsporum ripariae Microsporum rivalieri Doctor Fungus Mycology Unit at the Adelaide Women's and Children's Hospital
Vertebrate
Vertebrates comprise all species of animals within the subphylum Vertebrata. Vertebrates represent the overwhelming majority of the phylum Chordata, with about 69,276 species described. Vertebrates include the jawless fishes and jawed vertebrates, which include the cartilaginous fishes and the bony fishes; the bony fishes in turn, cladistically speaking include the tetrapods, which include amphibians, reptiles and mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, at up to 33 m. Vertebrates make up less than five percent of all described animal species; the vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, the lampreys, do. Hagfish do, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as "Craniata" when discussing morphology. Molecular analysis since 1992 has suggested that hagfish are most related to lampreys, so are vertebrates in a monophyletic sense.
Others consider them a sister group of vertebrates in the common taxon of craniata. The word vertebrate derives from the Latin word vertebratus. Vertebrate is derived from the word vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it and the gastrointestinal tract below. In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body; the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. The defining characteristic of a vertebrate is the vertebral column, in which the notochord found in all chordates has been replaced by a segmented series of stiffer elements separated by mobile joints. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon and coelacanth.
Jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills; the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch; the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their chordate relatives have more than 50 pairs of gills. In amphibians and some primitive bony fishes, the larvae bear external gills, branching off from the gill arches; these are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish being irrevocably lost early in the evolution of tetrapods.
While the more derived vertebrates lack gills, the gill arches form during fetal development, form the basis of essential structures such as jaws, the thyroid gland, the larynx, the columella and, in mammals, the malleus and incus. The central nervous system of vertebrates is based on a hollow nerve cord running along the length of the animal. Of particular importance and unique to vertebrates is the presence of neural crest cells; these are progenitors of stem cells, critical to coordinating the functions of cellular components. Neural crest cells migrate through the body from the nerve cord during development, initiate the formation of neural ganglia and structures such as the jaws and skull; the vertebrates are the only chordate group to exhibit cephalisation, the concentration of brain functions in the head. A slight swelling of the anterior end of the nerve cord is found in the lancelet, a chordate, though it lacks the eyes and other complex sense organs comparable to those of vertebrates.
Other chordates do not show any trends towards cephalisation. A peripheral nervous system branches out from the nerve cord to innervate the various systems; the front end of the nerve tube is expanded by a thickening of the walls and expansion of the central canal of spinal cord into three primary brain vesicles: The prosencephalon and rhombencephalon, further differentiated in the various vertebrate groups. Two laterally placed eyes form around outgrowths from the midbrain, except in hagfish, though this may be a secondary loss; the forebrain is well developed and subdivided in most tetrapods, while the midbrain dominates in many fish and some salamanders. Vesicles of the forebrain are paired, giving rise to hemispheres like the cerebral hemispheres in mammals; the resulting anatomy of the central nervous system, with a single hollow nerve cord topped by a series of vesicles, is unique to vertebrates. All invertebrates with well-developed brains, such as insects and squids, have a ventral rather than dorsal system of ganglions, with a split brain stem running on each side of the mouth or gut.
Vertebrates originated about 525 million years ago during the Cambrian explosion, which saw
Cell nucleus
In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, a few others including osteoclasts have many; the cell nucleus contains all of the cell's genome, except for a small fraction of mitochondrial DNA, organized as multiple long linear DNA molecules in a complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are structured in such a way to promote cell function; the nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, the nuclear matrix, a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole.
Because the nuclear envelope is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules and ions. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, a number of nuclear bodies exist, made up of unique proteins, RNA molecules, particular parts of the chromosomes; the best-known of these is the nucleolus, involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA; the nucleus was the first organelle to be discovered. What is most the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek.
He observed the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei; the nucleus was described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under the microscope when he observed an opaque area, which he called the "areola" or "nucleus", in the cells of the flower's outer layer, he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "cytoblast", he believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having described cells multiplying by division and believing that many cells would have no nuclei; the idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak and Rudolf Virchow who decisively propagated the new paradigm that cells are generated by cells.
The function of the nucleus remained unclear. Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus; this was the first time. This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "monerula", a structureless mass of primordial mucus. Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other animal groups, including amphibians and molluscs. Eduard Strasburger produced the same results for plants in 1884; this paved the way to assign the nucleus an important role in heredity. In 1873, August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity; the function of the nucleus as carrier of genetic information became clear only after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century.
The nucleus is the largest organelle in animal cells. In mammalian cells, the average diameter of the nucleus is 6 micrometres, which occupies about 10% of the total cell volume; the contents of the nucleus are held in the nucleoplasm similar to the cytoplasm in the rest of the cell. The fluid component of this is termed the nucleosol, similar to the cytosol in the cytoplasm. In most types of granulocyte, a white blood cell, the nucleus is lobated and can be bi-lobed, tri-lobed or multi-lobed; the nuclear envelope, otherwise known as nuclear membrane, consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres. The nuclear envelope encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing between the nucleoplasm and the cytoplasm; the outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum, is studded with ribosomes.
The space between the membranes is called the perinuclear space and is continuous with the RER lumen. Nuclear pores, which provide aqueous cha
Unicellular organism
A unicellular organism known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Prokaryotes include bacteria and archaea. Many eukaryotes are multicellular, but the group includes the protozoa, unicellular algae, unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells emerging 3.8–4 billion years ago. Although some prokaryotes live in colonies, they are not specialised into cells with differing functions; these organisms live together, each cell must carry out all life processes to survive. In contrast the simplest multicellular organisms have cells that depend on each other to survive. Most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms. Additionally, multicellularity appears to have evolved independently many times in the history of life.
Some organisms are unicellular, like Dictyostelium discoideum. Additionally, unicellular organisms can be multinucleate, like Plasmodium. Primitive protocells were the precursors to today's unicellular organisms. Although the origin of life is still a mystery, in the prevailing theory, known as the RNA world hypothesis, early RNA molecules would have been the basis for catalyzing organic chemical reactions and self-replication; the RNA world hypothesis assumes that RNA molecules could form in abiotic conditions, which would require nucleic acids and ribose to be present. Theoretical and experimental findings show that nucleic acids and sugars could have been synthesized in early prebiotic conditions. Compartmentalization was necessary for chemical reactions to be more as well as to differentiate reactions with the external environment. For example, an early RNA replicator ribozyme may have replicated other replicator ribozymes of different RNA sequences if not kept separate; when amphiphiles like lipids are placed in water, the hydrophobic tails aggregate to form micelles and vesicles, with the hydrophilic ends facing outwards.
Primitive cells used self-assembling fatty-acid vesicles to separate chemical reactions and the environment. Because of their simplicity and ability to self-assemble in water, it's that these simple membranes predated other forms of early biological molecules. Prokaryotes lack membrane-bound organelles, such as a nucleus. Instead, most prokaryotes have an irregular region. Most prokaryotes have a single, circular chromosome, in contrast to eukaryotes, which have linear chromosomes. Nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, ammonia, or nitrite. Prokaryotes as a whole exist in extreme environments as well. Bacteria are one of the world's oldest forms of life, are found everywhere in nature. Many common bacteria have plasmids, which are short, self-replicating DNA molecules that are separate from the bacterial chromosome. Plasmids can carry genes responsible for novel abilities, of current critical importance being antibiotic resistance.
Bacteria predominantly reproduce asexually through a process called binary fission. However, about 80 different species can undergo a sexual process referred to as natural genetic transformation. Transformation is a bacterial process for transferring DNA from one cell to another, is an adaptation for repairing DNA damage in the recipient cell. In addition, plasmids can be exchanged through the use of a pilus in a process known as conjugation; the photosynthetic cyanobacteria are arguably the most successful bacteria, changed the early atmosphere of the earth by oxygenating it. Stromatolites, structures made up of layers of calcium carbonate and trapped sediment left over from cyanobacteria and associated community bacteria, left behind extensive fossil records; the existence of stromatolites gives an excellent record as to the development of cyanobacteria, which are represented across the Archaean and Phanerozoic eons. Much of the fossilized stromatolites of the world can be found in Western Australia.
There, some of the oldest stromatolites have been found, some dating back to about 3,430 million years ago. Hydrothermal vents release heat and hydrogen sulfide, allowing extremophiles to survive using chemolithotrophic growth. Archaea are similar in appearance to bacteria, hence their original classification as bacteria, but have significant molecular differences most notably in their membrane structure and ribosomal RNA. By sequencing the ribosomal RNA, it was found that the Archaea most split from bacteria and were the precursors to modern eukaryotes, are more phylogenetically related to eukaryotes; as their name suggests, Archaea comes from a Greek word archaios, meaning original, ancient, or primitive. Some archaea inhabit the most biologically inhospitable environments on earth, this is believed to in some ways mimic the early, harsh conditions that life was exposed to. Examples of these Archaean extremophiles are as follows: Thermophiles, optimum growth temperature of 50 °C-110 °C, including the genera Pyrobaculum, Pyrodictium and Melanopyrus.
Psychrophiles, optimum growth temperature of less than 15 °C, including the genera Methanogenium and Halorubrum. Alkaliphiles, optimum growth pH of greater
Mollusca
Mollusca is the second largest phylum of invertebrate animals. The members are known as mollusks. Around 85,000 extant species of molluscs are recognized; the number of fossil species is estimated between 100,000 additional species. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs live in freshwater and terrestrial habitats, they are diverse, not just in size and in anatomical structure, but in behaviour and in habitat. The phylum is divided into 8 or 9 taxonomic classes, of which two are extinct. Cephalopod molluscs, such as squid and octopus, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species; the gastropods are by far the most numerous molluscs and account for 80% of the total classified species. The three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, the structure of the nervous system.
Other than these common elements, molluscs express great morphological diversity, so many textbooks base their descriptions on a "hypothetical ancestral mollusc". This has a single, "limpet-like" shell on top, made of proteins and chitin reinforced with calcium carbonate, is secreted by a mantle covering the whole upper surface; the underside of the animal consists of a single muscular "foot". Although molluscs are coelomates, the coelom tends to be small; the main body cavity is a hemocoel. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles; the generalized mollusc has three in bivalves. The brain, in species that have one, encircles the esophagus. Most molluscs have eyes, all have sensors to detect chemicals and touch; the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur.
All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults. The coelomic cavity is reduced, they have kidney-like organs for excretion. Good evidence exists for the appearance of gastropods and bivalves in the Cambrian period, 541 to 485.4 million years ago. However, the evolutionary history both of molluscs' emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still subjects of vigorous debate among scientists. Molluscs still are an important food source for anatomically modern humans. There is a risk of food poisoning from toxins which can accumulate in certain molluscs under specific conditions and because of this, many countries have regulations to reduce this risk. Molluscs have, for centuries been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye, sea silk, their shells have been used as money in some preindustrial societies. Mollusc species can represent hazards or pests for human activities.
The bite of the blue-ringed octopus is fatal, that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can kill, but their sophisticated, though produced, venoms have become important tools in neurological research. Schistosomiasis is transmitted to humans via water snail hosts, affects about 200 million people. Snails and slugs can be serious agricultural pests, accidental or deliberate introduction of some snail species into new environments has damaged some ecosystems; the words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, soft. Molluscus was itself an adaptation of Aristotle's τὰ μαλάκια ta malákia, which he applied inter alia to cuttlefish; the scientific study of molluscs is accordingly called malacology. The name Molluscoida was used to denote a division of the animal kingdom containing the brachiopods and tunicates, the members of the three groups having been supposed to somewhat resemble the molluscs.
As it is now known these groups have no relation to molluscs, little to one another, the name Molluscoida has been abandoned. The most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, the organization of the nervous system. Many have a calcareous shell. Molluscs have developed such a varied range of body structures, it is difficult to find synapomorphies to apply to all modern groups; the most general characteristic of molluscs is they are bilaterally symmetrical. The following are present in all modern molluscs: The dorsal part of the body wall is a mantle which secretes calcareous spicules, plates or shells, it overlaps the body with enough spare room to form a mantle cavity. The anus and genitals open into the mantle cavity. There are two pairs of main nerve cords. Other characteristics that appear in textbooks have significant exceptions: Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species.
In 1969 David Nicol estimated the probable total number of living mollusc species at 107,000 of which were ab
Opisthosporidia [videos]
Opisthosporidia or Fungi are a sister clade of the Cristidiscoidea together forming the Holomycota. A basal group is the'basal clone group 2'. The other basal Opisthosporidan clade are the Aphelida together with the True Fungi, joined with the'basal clone group 1' …
Sporoblast of Fibrillanosema crangonycis (Microsporidian)
Image: Nuclearia sp Nikko
Spore [videos]
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a …
Fresh snow partially covers rough-stalked feather-moss (Brachythecium rutabulum), growing on a thinned hybrid black poplar (Populus x canadensis). The last stage of the moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is still attached to the capsule (2). The tops of the gametophytes (3) can be discerned as well. Inset shows the surrounding, black poplars growing on sandy loam on the bank of a kolk, with the detail area marked.
Asci of Morchella elata, containing ascospores
Image: Bartramia ithyphylla sporen
Image: Fernspore 1
Unicellular organism [videos]
A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Prokaryotes …
Modern stromatolites in Shark Bay, Western Australia. It can take a century for a stromatolite to grow 5 cm.
Paramecium tetraurelia, a ciliate, with oral groove visible
A scanning electron microscope image of a diatom
Transmission electron microscope image of budding Ogataea polymorpha
Parasitism [videos]
In evolutionary biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has characterised parasites as "predators that eat …
A fish parasite, the isopod Cymothoa exigua, replacing the tongue of a Lithognathus
Human head lice are directly-transmitted obligate ectoparasites.
Schistosoma mansoni an obligate directly-transmitted endoparasite, causes schistosomiasis (snail fever).
The vector-transmitted protozoan endoparasite Trypanosoma among human red blood cells
Protozoa [videos]
Protozoa is an informal term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. Historically, the protozoa were regarded as "one-celled animals", because they …
Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmerella moniliformis, a choanoflagellate
John Hogg's illustration of the Four Kingdoms of Nature, showing "Primigenal" as a greenish haze at the base of the Animals and Plants, 1860
The ciliate Spirostomum ambiguum can attain 3 mm in length
Isotricha intestinalis, a ciliate present in the rumen of sheep.
Host (biology) [videos]
In biology and medicine, a host is an organism that harbours a parasitic, a mutualistic, or a commensalist guest, the guest typically being provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic …
The black rat is a reservoir host for bubonic plague: the oriental rat fleas that infest these rats are vectors for the disease.
Mycorrhiza, a mutualistic interaction between a plant's roots and a fungus
Cleaning symbiosis: a Hawaiian cleaner wrasse with its client, a yellowtail wrasse
Nurse shark playing host to commensal remoras, which gain a free ride and which may serve as cleaners
Insect [videos]
Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta is synonymous with Ectognatha. Insects have a …
Evolution has produced enormous variety in insects. Pictured are some possible shapes of antennae.
A pair of Simosyrphus grandicornis hoverflies mating in flight.
A pair of grasshoppers mating.
The different forms of the male (top) and female (bottom) tussock moth Orgyia recens is an example of sexual dimorphism in insects.
Crustacean [videos]
Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill, woodlice, and barnacles. — The crustacean group is usually treated as a subphylum, and because of recent molecular studies it is now well accepted that the …
Abludomelita obtusata, an amphipod
A shed carapace of a lady crab, part of the hard exoskeleton
Body structure of a typical crustacean – krill
Eggs of Potamon fluviatile, a freshwater crab
Fish [videos]
Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods …
Giant grouper swimming among schools of other fish
Head-on view of a red lionfish
A relative of the seahorses, the leafy seadragon's appendages allow it to camouflage (in the form of crypsis) with the surrounding seaweed.
Tuna gills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth.
Mammal [videos]
Mammals are vertebrate animals constituting the class Mammalia, and characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, and three middle ear bones. These …
Bovine kidney
A bonobo fishing for termites with a stick
Red kangaroos "boxing" for dominance
Upper Paleolithic cave painting of a variety of large mammals, Lascaux, c. 17,300 years old
Flagellum [videos]
A flagellum is a lash-like appendage that protrudes from the cell body of certain bacteria and eukaryotic cells termed as flagellates. A flagellate can have one or several flagella. The primary function of a flagellum is that of locomotion, but it also often functions as a …
SEM image of flagellated Chlamydomonas sp. (10000×)
Physical model of a bacterial flagellum
Longitudinal section through the flagella area in Chlamydomonas reinhardtii. In the cell apex is the basal body that is the anchoring site for a flagellum. Basal bodies originate from and have a substructure similar to that of centrioles, with nine peripheral microtubule triplets (see structure at bottom center of image).
Image: Chlamydomonas TEM 17
Cell nucleus [videos]
In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including …
HeLa cells stained for nuclear DNA with the blue fluorescent Hoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed.
Oldest known depiction of cells and their nuclei by Antonie van Leeuwenhoek, 1719
A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. "Begin" indicates the 5' end of the DNA, where new RNA synthesis begins; "end" indicates the 3' end, where the primary transcripts are almost complete.
Image: Flemming 1882Tafel 1Fig 14
Asexual reproduction [videos]
Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. Asexual reproduction is the primary form of reproduction for …
Asexual reproduction in liverworts: a caducous phylloid germinating
The yeast Saccharomyces cerevisiae reproducing by budding
Vegetative plantlets of mother-of-thousands, Bryophyllum (Kalanchoe) daigremontianum
Linckia guildingi "comet", a starfish regrowing from a single arm
Vertebrate [videos]
Vertebrates comprise all species of animals within the subphylum Vertebrata. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,276 species described. Vertebrates include the jawless fishes and jawed vertebrates, which …
Fossilized skeleton of Diplodocus carnegii, showing an extreme example of the backbone that characterizes the vertebrates.
Gill arches bearing gills in a pike
Acanthostega, a fish-like early labyrinthodont.
Traditional spindle diagram of the evolution of the vertebrates at class level
Mollusca [videos]
Mollusca is the second largest phylum of invertebrate animals. The members are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species.Molluscs are the largest marine phylum …
Tonicella lineata, a polyplacophoran or chiton, anterior end towards the right
Diversity and variability of shells of molluscs on display.
The use of love darts by the land snail Monachoides vicinus is a form of sexual selection
Some wool dipped in techelet solution, from the Murex trunculus, turns blue in the sunlight outside P'til Techelet in Israel.
Bacteria [videos]
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the …
Scanning electron micrograph of Escherichia coli rods
An electron micrograph of Halothiobacillus neapolitanus cells with carboxysomes inside, with arrows highlighting visible carboxysomes. Scale bars indicate 100 nm.
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
Fungus [videos]
A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, fungi, which is separate from the other eukaryotic life kingdoms of …
Omphalotus nidiformis, a bioluminescent mushroom
The bird's nest fungus Cyathus stercoreus
Image: Fungi collage
Culex [videos]
Culex is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nile virus, Japanese encephalitis, or St. Louis encephalitis, but also filariasis and …
Culex pipiens, female
Culex malariager in amber
Plasmodium falciparum [videos]
Plasmodium falciparum is a unicellular protozoan parasite of humans, and the deadliest species of Plasmodium that cause malaria in humans. It is transmitted through the bite of a female Anopheles mosquito. It is responsible for roughly 50% of all malaria cases. It causes the disease's most …
Laveran's drawing of various stages of P. falciparum as seen on fresh blood (1880).
Blood smear from a P. falciparum culture (K1 strain - asexual forms) - several red blood cells have ring stages inside them. Close to the center is a schizont and on the left a trophozoite.
Macrogametocyte (left) and microgametocyte (right) of P. falciparum
Eukaryote [videos]
Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, unlike prokaryotes, which have no membrane-bound organelles. Eukaryotes belong to the domain Eukaryota or Eukarya. Their name comes from the Greek εὖ and κάρυον (karyon …
Eukaryotes and some examples of their diversity – clockwise from top left: Red mason bee, Boletus edulis, chimpanzee, Isotricha intestinalis, Ranunculus asiaticus, and Volvox carteri
Konstantin Mereschkowski proposed a symbiotic origin for cells with nuclei.
Microsporum [videos]
Microsporum is a genus of fungi that causes tinea capitis, tinea corporis, ringworm, and other dermatophytoses. Microsporum forms both macroconidia and microconidia on short …
Microsporum canis
Microsporum gypseum
Protist [videos]
A protist is any eukaryotic organism that is not an animal, plant or fungus. The protists do not form a natural group, or clade, since they exclude certain eukaryotes; but, like algae or invertebrates, they are often grouped together for convenience. In some …
Image: Protist collage 2
Image: Biomass by life form
Incertae sedis [videos]
Incertae sedis or problematica are terms used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty at specific …
New World vultures, such as the California condor, were placed incertae sedis within the Class Aves until the recognition of the new Order Cathartiformes.
Plumalina plumaria Hall, 1858 (6.3 cm tall), Upper Devonian of western New York State, USA. Workers usually assign this organism to the hydrozoans (Phylum Cnidaria, Class Hydrozoa) or the gorgonarians (Phylum Cnidaria, Class Anthozoa, Order Gorgonaria), but it's probably safest to refer to it as incertae sedis.
Chitin [videos]
Chitin n, a long-chain polymer of N-acetylglucosamine, is a derivative of glucose. It is a primary component of cell walls in fungi, the exoskeletons of arthropods, such as crustaceans and insects, the radulae of molluscs, cephalopod beaks …
A close-up of the wing of a leafhopper; the wing is composed of chitin.
A cicada emerges from its chitinous larval exoskeleton.
Golgi apparatus [videos]
The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian scientist Camillo Golgi and named after him in 1898.Part of the endomembrane system in the cytoplasm, the Golgi apparatus …
Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. Numerous circular vesicles can be seen in proximity to the organelle.
Image: Golgi Scyl 1c
Ribosomal RNA [videos]
Ribosomal ribonucleic acid is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight, or 3/5 of ribosome mass. Ribosomes contain …
Image: RF00177
Three-dimensional views of the ribosome, showing rRNA in dark blue (small subunit) and dark red (large subunit). Lighter colors represent ribosomal proteins.
Microspora [videos]
Microspora is a genus of green algae in the family Microsporaceae. Microspora are autotrophic fungus-like protists that are often characterized by their many segments. — References …
Image: Microsporaceae
Sphaerius [videos]
Sphaerius is a genus of beetles, comprising 23 species, which are the only members of the family Sphaeriusidae. They are typically found along the edges of streams and rivers, where they feed on algae; they occur on all continents except Antarctica. Three species occur in the United States. — The …
Sphaerius acaroides
Synonym (taxonomy) [videos]
In scientific nomenclature, a synonym is a scientific name that applies to a taxon that goes by a different scientific name, although the term is used somewhat differently in the zoological code of nomenclature. For example, Linnaeus was the first to give a scientific name (under the …
The Latin Caudata and Greek Urodela both mean "tailed" and have been used as a scientific name at the taxonomic rank of order for the salamanders (as opposed to the tail-less frogs). Thus they are synonyms.
Parasitic castration [videos]
Parasitic castration is the strategy, by a parasite, of blocking reproduction by its host, completely or in part, to its own benefit. This is one of six major strategies within parasitism. — For example, Hemioniscus balani, a parasitic castrator of hermaphroditic barnacles, feeds on ovarian fluid, so …
Image: Sacculina carcini
Xenoma [videos]
A xenoma is a growth caused by various protists and fungi, most notably microsporidia. It can occur on numerous organisms; however is predominantly found on fish.In most cases the host cell and nuclei suffers from hypertrophy resulting in a change in …
Image: Glugea stephani
Genome [videos]
In the fields of molecular biology and genetics, a genome is the genetic material of an organism. It consists of DNA. The genome includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA. The study of the genome is …
An image of the 46 chromosomes making up the diploid genome of a human male. (The mitochondrial chromosome is not shown.)
Mitochondrion [videos]
The mitochondrion is a double-membrane-bound organelle found in most eukaryotic organisms. Some cells in some multicellular organisms may, however, lack them. A number of unicellular organisms, such as microsporidia …
Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy
Plasmodium (life cycle) [videos]
A plasmodium is a living structure of cytoplasm that contains many nuclei, rather than being divided into individual cells each with a single nucleus. — Plasmodia are best known from slime molds, but are also found in parasitic Myxosporea, and some algae such as the Chlorarachniophyta. — Structure …
Plasmodiocarp of the slime mold Hemitrichia serpula: the living structure contains many nuclei, not separated from each other by cell membranes or cell walls.
Anopheles gambiae [videos]
The Anopheles gambiae complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus Anopheles. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub-Saharan Africa, particularly of the most dangerous malaria …
Image: Anopheles Gambiaemosquito