ithycythara pentagonalis is a species of sea snail , a marine gastropod mollusk in the family mangeliidae .

tucker considers ithycythara auberiana a synonym of ithycythara pentagonalis reeve , l.a. , 1845

ithycythara pentagonalis

ithycythara pentagonalis <EOT> ithycythara pentagonalis reeve , l . a . , 1845 : st vincent , west indies

ithycythara is a genus of sea snails , marine gastropod mollusks in the family mangeliidae .

species pleurotoma acutangulus e . a . smith , 1882 accepted as ithycythara acutangulus ( e . a . smith , 1882 ) ( original combination )

fonte : wikipedia . paginas : 90 . capitulos : bela , eucithara , lienardia , mangelia , pseudorhaphitoma , guraleus , anacithara , antiguraleus , pyrgocythara , kurtziella , ithycythara , benthomangelia , clathromangelia , mangiliella , brachycythara , tenaturris , citharomangelia , leiocithara , heterocithara , neoguraleus , pleurotomoides , cryoturris , turrella , thelecythara , paraclathurella , anticlinura , paramontana , belaturricula , marita , kurtzia , benthomangelia abyssopacifica , gingicithara , neoguraleus interruptus , glyphoturris , thelecytharella , benthomangelia subtrophonoidea , austropusilla , belaturricula dissimilis , brachycythara multicinctata , belaturricula antarctica , ithycythara apicodenticulata , acmaturris , glyptaesopus , benthomangelia trophonoidea , benthomangelia gracilispira , clathromangelia fuscoligata , clathromangelia loiselieri , benthomangelia decapitata , clathromangelia strigilata , clathromangelia variegata , euclathurella , benthomangelia celebensis , pyrgocythara candidissima , pyrgocythara densestriata , belaturricula turrita , benthomangelia brachytona , pseudorhaphitoma perplexior , pseudorhaphitoma unicostata , platycythara , clathromangelia quadrillum , ithycythara septemcostata , thelecythara dominguezi , brachycythara beatriceae , clathromangelia coffea , pyrgocythara albovittata , brachycythara atlantidea , pyrgocythara fuscoligata , pyrgocythara subdiaphana , belaturricula ergata , pseudorhaphitoma kilburni , pyrgocythara urceolata , cryoturris quadrilineata , ithycythara funicostata , ithycythara pentagonalis , ithycythara acutangulus , macteola , pyrgocythara hemphilli , benthomangelia bandella , kurtziella margaritifera , clathromangelia granum , mangelia pseudoattenuata , brachycythara biconica , clathromangelia strigillata , belaturricula gaini , benthomangelia brevis , clathromangelia rhyssa , brachycythara stegeri , ithycythara lanceolata , ithycythara muricoides , pyrgocythara angulosa , thelecythara dushanae , benthomangelia antonia , glyptaesopus proctorae , pyrgocythara cinctella , pyrgocythar . . .

5 / 12 / 2009 10 : 29 am - peggy williams added to harry ' s comments with : " i agree with harry that marlo ' s shell is more likely rubricata and that pentagonalis and auberiana may be synonymous ( in fact , someone has determined so , since malacolog has them synonymized . ) but i think parkeri is distinctly more slender and has fewer ribs than the others . "

id : 280182 original name : ithycythara _ pentagonalis9 . jpg size 666x414 - 87237 bytes image manager : jan delsing directory : 3810 created : 2015 - 11 - 08 12 : 26 : 53 - user jan delsing last change : 2015 - 11 - 08 12 : 27 : 24 - user jan delsing url : urltoken text function : [ [ i : 280182 ; image ] ] , [ [ it : 280182 ] ] ( thumbnail )

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version 43 . 0 went live 11 / 6 / 2018 - i hope that the majority of issues have been fixed . my email address is on the home page if you see anything wrong .

vol . 2 mollusques , p 174 ; pl . 24 / 4 - 6

confused by a class within a class or an order within an order ? please see our brief essay .

to cite this page : myers , p . , r . espinosa , c . s . parr , t . jones , g . s . hammond , and t . a . dewey . 2018 . the animal diversity web ( online ) . accessed at https : / / animaldiversity . org .

disclaimer : the animal diversity web is an educational resource written largely by and for college students . adw doesn ' t cover all species in the world , nor does it include all the latest scientific information about organisms we describe . though we edit our accounts for accuracy , we cannot guarantee all information in those accounts . while adw staff and contributors provide references to books and websites that we believe are reputable , we cannot necessarily endorse the contents of references beyond our control .

this material is based upon work supported by the national science foundation grants drl 0089283 , drl 0628151 , due 0633095 , drl 0918590 , and due 1122742 . additional support has come from the marisla foundation , um college of literature , science , and the arts , museum of zoology , and information and technology services .

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the star system calculates the number of pieces that were handled by conchology , inc . in the last 15 years :

we want to point out that the star system is only very reliable for philippine shells only , as we handle very few foreign shells in general . as time goes , the system will become more and more performant .

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click on an image to view a larger image of that shell . author , date , and full locality are given on the labels with shells .

philippines . mactan . punta engano . taken with lumun lumun nets , 100 - 150 m . collected by local fishermen . 2009 .

philippines . cebu . lilo - an . collected at 50 - 150 m . 2008 .

philippines . olango island . 20 - 25 m . from local fishermen . 2008

philippines . palawan . balabac island . dived about 25 m . by fishermen from olango . 2006 .

philippines . mactan island . taken 80 - 100 m . with lumun lumun nets . 2003 .

philippines . north of cebu . liloan . 10 - 25 m . 2017 .

philippines . olango island . 10 - 25 m . collected by local fishermen . 2010 .

philippines . butuan . trawled at 50 - 100 m . collected by local fishermen . 2010 .

philippines . nocnocan island . 20 - 50 m . collected by local fishermen . 2010 .

philippines . palawan . taken between 10 and 25 meters deep water . from local fishermen . 2010 .

philippines . bohol . nocnocan island . 10 - 25 m . collected by local fishermen . 2009 .

philippines . palawan . found at about 10 - 25 m . collected by local fishermen . 2009 .

philippines . palawan . balabac island . taken 10 - 15 m . collected by local fishermen . 2009 .

philippines . olango island . dived , 15 - 30 m . collected by local fishermen . 2009 .

philippines . palawan . taken at 10 - 25 m . collected by local fishermen . 2009 .

philippines . olango island . taken at 10 - 25 m . collected by local fishermen . 2008 .

philippines . bohol . near pandakan island . scuba 18 m . - guphil i - 2004 . hypo .

philippines . north of cebu . liloan . tangle nets . 8 - 12 m . 2017 .

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discussions , photo series , how to identify or distinguish a species or between species .

was " common . " however , it appears this is a sublittoral species and probably rarely found except as a beach shell .

the one specimen i have was collected at the artificial and unique inlet habitat at palm beach and is not representative of normal habitat for many , many of the species collected there . i was wondering if anyone has had the good fortune to collect this shell live anywhere in florida by any means ? "

" i am pretty sure that i had this species in dredgings , in the days when you could get them . i have traded most of my small shells for pectinidae , so i cannot check . "

as full species without synonyms . searches of the florida museum of natural history’s invertebrate zoology master database and the bailey - matthews shell museum database revealed no records of any of these four names . )

5 / 12 / 2009 11 : 45 am - harry added : " dear peggy , marlo et al . , reeve ( 1845 : sp . 255 ) and abbott ( 1958 : 96 ) described shells with five axial ribs . abbott failed to compare his species with reeve ' s . i agree that the profile of the abbott ' s species ( type figure ) is a bit stouter . harry reeve , l . , 1843 - 1846 . the genus pleurotoma . conchologia iconica 1 : 40 pls . , facing text blocks + index . jan . - apr . abbott , r . t . , 1958 . the marine mollusks of grand cayman island , british west indies . monographs of the acad . nat . sci . phila . 11 : vi + pp . 1 - 138 + 5 pls . + index . "

marlo ' s comment : thanks to all for comments and hopefully there will be more . harry ' s and linda ' s comments appear to confirm that

is a sublittoral species and probably collectable as a live shell only when dredged , but for exceptional circumstances . as to the name issue , i ' ll stay with

- note : several protected species are illustrated here only for identification purposes . they are not for sale . - the photos in our gallery are in most cases just a sample from our stock , except when only one specimen is offered . we try to match the original color but it can vary if your screen is not correctly adjusted ( gamma correction ) .

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» species pleurotoma ( bela ) violacea ( mighels & c . b . adams , 1842 ) accepted as curtitoma violacea ( mighels & c . b . adams , 1842 )

» species pleurotoma ( clathurella ) commutabilis e . a . smith , 1890 accepted as mitromorpha commutabilis ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( clathurella ) horneana e . a . smith , 1884 accepted as clathurella horneana ( e . a . smith , 1884 )

» species pleurotoma ( clathurella ) letourneuxiana crosse & p . fischer , 1865 accepted as turrella letourneuxiana ( crosse & p . fischer , 1865 ) ( basionym )

» species pleurotoma ( clathurella ) lucida e . a . smith , 1884 accepted as pseudodaphnella lucida ( e . a . smith , 1884 ) ( basionym )

» species pleurotoma ( clathurella ) multigranosa e . a . smith , 1890 accepted as mitromorpha multigranosa ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( clathurella ) perinsignis e . a . smith , 1884 accepted as raphitoma perinsignis ( e . a . smith , 1884 ) ( basionym )

» species pleurotoma ( clathurella ) usta e . a . smith , 1890 accepted as mitromorpha usta ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( clavus ) albobalteata e . a . smith , 1890 accepted as austrodrillia albobalteata ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( clavus ) amanda e . a . smith , 1882 accepted as drillia sinuosa ( montagu , 1803 )

» species pleurotoma ( clavus ) hottentota e . a . smith , 1882 accepted as clavus hottentotus ( e . a . smith , 1882 )

» species pleurotoma ( clavus ) interpunctata e . a . smith , 1882 accepted as splendrillia interpunctata ( e . a . smith , 1882 ) ( basionym )

» species pleurotoma ( clavus ) prolongata e . a . smith , 1890 accepted as inodrillia prolongata ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( defrancia ) asperulata e . a . smith , 1882 accepted as veprecula pungens ( gould , 1860 )

» species pleurotoma ( drillia ) amoena e . a . smith , 1884 accepted as neoguraleus amoenus ( e . a . smith , 1884 ) ( original combination )

» species pleurotoma ( drillia ) atkinsonii e . a . smith , 1877 accepted as drillia crenularis ( lamarck , 1816 ) accepted as ptychobela nodulosa ( gmelin , 1791 )

» species pleurotoma ( drillia ) baynhami e . a . smith , 1891 accepted as ptychobela baynhami ( e . a . smith , 1891 ) ( basionym )

» species pleurotoma ( drillia ) cookei e . a . smith , 1888 accepted as syntomodrillia cookei ( e . a . smith , 1888 ) ( basionym )

» species pleurotoma ( drillia ) essingtonensis e . a . smith , 1888 accepted as inquisitor mastersi ( brazier , 1876 )

» species pleurotoma ( drillia ) incerta e . a . smith , 1877 accepted as inquisitor incertus ( e . a . smith , 1877 ) ( basionym )

» species pleurotoma ( drillia ) intertincta e . a . smith , 1877 accepted as inquisitor intertinctus ( e . a . smith , 1877 ) ( basionym )

» species pleurotoma ( drillia ) latisinuata e . a . smith , 1877 accepted as funa latisinuata ( e . a . smith , 1877 ) ( basionym )

» species pleurotoma ( drillia ) mindanensis e . a . smith , 1877 accepted as cheungbeia mindanensis ( e . a . smith , 1877 ) ( basionym )

» species pleurotoma ( drillia ) nodilirata e . a . smith , 1877 accepted as clavus nodiliratus ( e . a . smith , 1877 )

» species pleurotoma ( drillia ) subochracea e . a . smith , 1877 accepted as aguilaria subochracea ( e . a . smith , 1877 ) ( basionym )

» species pleurotoma ( drillia ) torresiana e . a . smith , 1884 accepted as inquisitor sterrha ( r . b . watson , 1881 )

» species pleurotoma ( drillia ) turtoni e . a . smith , 1890 accepted as glyphostoma turtoni ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( hemipleurotoma ) alticincta r . murdoch & suter , 1906 accepted as iredalula alticincta ( murdoch & suter , 1906 ) ( original combination )

» species pleurotoma ( leucosyrinx ) augusta r . murdoch & suter , 1906 accepted as paracomitas augusta ( murdoch & suter , 1906 )

» species pleurotoma ( leucosyrinx ) eremita r . murdoch & suter , 1906 accepted as leucosyrinx eremita ( murdoch & suter , 1906 ) ( original combination )

» species pleurotoma ( mangelia ) hypsela r . b . watson , 1881 accepted as syntomodrillia hypsela ( r . b . watson , 1881 ) ( basionym )

» species pleurotoma ( mangelia ) lallemantiana crosse & p . fischer , 1865 accepted as guraleus lallemantianus ( crosse & p . fischer , 1865 ) ( basionym )

» species pleurotoma ( mangelia ) mellissii e . a . smith , 1890 accepted as mangelia mellissii ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( mangelia ) vincentina crosse & p . fischer , 1865 accepted as guraleus pictus ( a . adams & angas , 1864 )

» species pleurotoma ( mangilia ) atlantica e . a . smith , 1890 represented as pleurotoma atlantica e . a . smith , 1890

» species pleurotoma ( mangilia ) albolabiata e . a . smith , 1884 accepted as mangelia albolabiata ( e . a . smith , 1884 ) ( basionym )

» species pleurotoma ( mangilia ) coppingeri e . a . smith , 1881 accepted as savatieria coppingeri ( e . a . smith , 1881 ) ( basionym )

» species pleurotoma ( mangilia ) mellissi e . a . smith , 1890 accepted as stellatoma mellissi ( e . a . smith , 1890 ) ( basionym )

» species pleurotoma ( mangilia ) ordinaria e . a . smith , 1882 accepted as agathotoma ordinaria ( e . a . smith , 1882 ) ( basionym )

» species pleurotoma ( mangilia ) pellyi e . a . smith , 1882 accepted as mangelia pellyi ( e . a . smith , 1882 ) ( basionym )

» species pleurotoma ( mangilia ) sinclairii e . a . smith , 1884 accepted as neoguraleus finlayi powell , 1942

» species pleurotoma ( mangilia ) subquadrata e . a . smith , 1888 accepted as clathurella subquadrata ( e . a . smith , 1888 ) ( basionym )

» species pleurotoma ( mangilia ) trizonata e . a . smith , 1882 accepted as neoguraleus trizonata ( e . a . smith , 1882 ) ( basionym )

» species pleurotoma ( perrona ) marmarina r . b . watson , 1881 accepted as fenimorea marmarina ( r . b . watson , 1881 ) ( basionym )

» species pleurotoma ( pleurotomella ) pandionis verrill , 1880 accepted as pleurotomella pandionis ( a . e . verrill , 1880 ) ( original combination )

subgenus pleurotoma ( spirotropis ) g . o . sars , 1878 accepted as spirotropis g . o . sars , 1878

subgenus pleurotoma ( surcula ) accepted as surcula h . adams & a . adams , 1853 accepted as turricula schumacher , 1817

» species pleurotoma ( surcula ) goniodes r . b . watson , 1881 accepted as aforia goniodes ( r . b . watson , 1881 ) ( basionym )

» species pleurotoma ( surcula ) lepta r . b . watson , 1881 accepted as aforia watsoni kantor , harasewych & puillandre , 2016

» species pleurotoma ( thesbia ) translucida r . b . watson , 1881 accepted as xanthodaphne translucida ( r . b . watson , 1881 ) ( basionym )

species pleurotoma acanthodes r . b . watson , 1881 accepted as kurtziella acanthodes ( r . b . watson , 1881 ) ( original combination )

species pleurotoma acuminata mighels , 1845 accepted as pyrgocythara mighelsi ( kay , 1979 ) ( invalid : junior homonym of pleurotoma acuminata j . sowerby , 1816 ; clavus mighelsi is a replacement name )

species pleurotoma acutigemmata e . a . smith , 1877 accepted as turridrupa acutigemmata ( e . a . smith , 1877 ) ( original combination )

species pleurotoma adamsii e . a . smith , 1884 accepted as cryoturris adamsii ( e . a . smith , 1884 ) ( original combination )

species pleurotoma adelpha dautzenberg & fischer h . , 1896 accepted as phymorhynchus sulciferus ( bush , 1893 ) ( synonym )

species pleurotoma agalma e . a . smith , 1906 accepted as paradrillia agalma ( e . a . smith , 1906 ) ( original combination )

species pleurotoma aganactica r . b . watson , 1886 accepted as spirotropis aganactica ( r . b . watson , 1886 ) ( original combination )

species pleurotoma agassizi verrill & s . smith , 1880 accepted as gymnobela agassizii ( verrill & s . smith [ in verrill ] , 1880 )

species pleurotoma agassizii verrill & s . smith [ in verrill ] , 1880 accepted as gymnobela agassizii ( verrill & s . smith [ in verrill ] , 1880 ) ( original combination )

species pleurotoma aglaophanes r . b . watson , 1882 accepted as clionella aglaophanes ( r . b . watson , 1882 ) ( original combination )

species pleurotoma albata e . a . smith , 1882 accepted as etremopsis albata ( e . a . smith , 1882 ) ( original combination )

species pleurotoma albicarinata g . b . sowerby ii , 1870 accepted as polystira oxytropis ( g . b . sowerby i , 1834 )

species pleurotoma albicaudata e . a . smith , 1882 accepted as kermia albicaudata ( e . a . smith , 1882 ) ( original combination )

species pleurotoma albida perry g . , 1811 accepted as polystira albida ( g . perry , 1811 ) ( original combination )

species pleurotoma albida deshayes , 1835 accepted as mangelia unifasciata ( deshayes , 1835 ) ( invalid : junior homonym of pleurotoma albida perry , 1811 and p . albida risso , 1826 )

species pleurotoma alboangulata e . a . smith , 1882 accepted as carinodrillia alboangulata ( e . a . smith , 1882 ) ( original combination )

species pleurotoma albocincta c . b . adams , 1845 accepted as pilsbryspira albocincta ( c . b . adams , 1845 ) ( original combination )

species pleurotoma albofasciata e . a . smith , 1877 accepted as turridrupa albofasciata ( e . a . smith , 1877 ) ( original combination )

species pleurotoma albolabiata e . a . smith , 1884 accepted as mangelia albolabiata ( e . a . smith , 1884 ) ( original combination )

species pleurotoma albomaculata c . b . adams , 1845 accepted as drillia albomaculata ( c . b . adams , 1845 ) ( original combination )

species pleurotoma albomaculata d ' orbigny , 1847 accepted as pilsbryspira nodata ( c . b . adams , 1850 ) ( non c . b . adams , 1845 )

species pleurotoma albovittata c . b . adams , 1845 accepted as pyrgocythara albovittata ( c . b . adams , 1845 ) ( original combination )

species pleurotoma alternans e . a . smith , 1882 accepted as pseudodaphnella alternans ( e . a . smith , 1882 ) ( original combination )

species pleurotoma amanda e . a . smith , 1882 accepted as drillia sinuosa ( montagu , 1803 )

species pleurotoma amicta e . a . smith , 1877 accepted as turris amicta ( e . a . smith , 1877 ) ( original combination )

species pleurotoma amoena ( e . a . smith , 1884 ) accepted as neoguraleus amoenus ( e . a . smith , 1884 )

species pleurotoma angustae c . b . adams , 1850 accepted as decoradrillia pulchella ( reeve , 1845 )

species pleurotoma anteridion r . b . watson , 1881 accepted as comitas anteridion ( r . b . watson , 1881 ) ( original combination )

species pleurotoma arafurensis e . a . smith , 1884 accepted as daphnella arafurensis ( e . a . smith , 1884 ) ( original combination )

species pleurotoma araneosa r . b . watson , 1881 accepted as xanthodaphne araneosa ( r . b . watson , 1881 ) ( original combination )

species pleurotoma arcana e . a . smith , 1899 accepted as comitas arcana ( e . a . smith , 1899 ) ( original combination )

, invalid : not pleurotoma pagoda reeve , 1845 . p . alta harris , 1897 is replacement name )

grammatical gender feminine , as composed with the greek noun τομή , an incision ( gender : feminine ) . however philippi ( 1836 : 165 , footnote ) and others defended treating it as neuter . [ details ]

1 marine biology department , universidade federal fluminense , p . o . box 100 . 644 , niterói , rj , brazil

abstract . biogeographic distributional patterns of gastropods are proposed based on the species ' geo - graphic and bathymetric distribution . samples were collected along the brazilian continental margin between 18° s and 23° s , at 37 stations with depths from 20 m to 1 , 330 m . the analysis of the biogeographic distribution patterns confirmed the existence of a transitional zone from tropical to subtropical waters in the area of both the continental shelf and slope , suggesting a relationship with water mass circulation . we observed a high species turnover rate between the shelf and slope . the analysis of gastropod species distribution revealed a similar pattern on the shelf and slope and a large difference between shallow and deep - water faunas .

keywords : macrobenthos , continental margins , geographical distribution , vertical distribution , soft bottoms , brazil , southwestern atlantic ocean .

resumen . los patrones de distribución biogeográfica de gastrópodos fueron propuestos basados en la distribución geográfica y batimétrica de las especies . los muestreos fueron realizados en el margen continental brasileño entre 18°s y 23°s , en 37 estaciones de 20 m a 1 . 330 m de profundidad . el análisis de los patrones de distribución biogeográfica confirmó la existencia de una zona de transición de aguas tropicales a aguas subtropicales , que se encuentra en la zona de la plataforma continental y también en la zona del talud continental , esto puede sugerir una relación con la circulación de las masas de agua . se observó una elevada tasa de turnover de las especies entre la plataforma y el talud continental . el análisis de las especies de gastrópodos reveló un patrón similar tanto en la plataforma como en el talud y una gran diferencia entre las faunas de las aguas someras y profundas .

palabras clave : macrobentos , margen continental , distribución geográfica , distribución vertical , fondos blandos , brasil , océano atlántico sudoccidental .

understanding the patterns of the geographic distribution of life is a very oíd issue in biology , and one that continues to be debated . in the sea , geographic patterns ( e . g . , in species assemblages and diversity ) have been described for both shallow and deep - sea fauna ( rex , 1993 ; rex et al , 1993 ; clarke & crame , 1997 ; gray , 1998 ; willig et al , 2003 ; hillebrand , 2004 ) .

longitudinal and latitudinal barriers represented by the arrangement of land masses and oceans , by temperatura gradients , and by hydrodynamic patterns and water properties divide the oceans into a series of biogeographic realms with their own characteristic species assemblages ( briggs , 1995 ; longhurst , 1998 ) . the sea surface temperature is supposed to be the main forcé limiting the latitudinal distribution of marine species . therefore , biogeographic realms are not expected to be the same along a depth gradient . in general , the wider a species ' vertical distributional range , the wider its geographical distribution ( harley et al , 2003 ) . eurybathic taxa ( those with a broader vertical range ) show a wider horizontal distribution than stenobathic taxa ( those with a narrow vertical range ) ( vinogradova , 1997 ) . due to the fact that deep - sea species are mainly stenobathic , abyssal and hadal fauna show higher levels of endemism ( vinogradova , 1997 ; zezina , 1997 ) . the bulk of shallow - sea fauna is also stenobathic but , according to menzies et al . ( 1973 ) , the fauna on the continental slope has a wider geographical distribution than that of any other vertical faunal zone .

several authors have discussed zoogeographic and diversity patterns for brazilian shallow waters based on benthic invertebrates ( e . g . , briggs , 1974 ; semenov , 1978 ; kempf , 1979 ; palacio , 1982 ; floeter & soares - gomes , 1999 ) , but few have discussed biogeographic patterns of the neighbouring slope or abyssal zones ( alien & sanders , 1996 is a good example for abyssal basins ) .

the effect of the latitudinal gradient is so strong on the species diversity of marine molluscs that it is also evident at the genus and family level ( roy et al . , 1998 ; crame , 2000 ) and recognized in fossil assemblages ( crame , 2002 ; jablonski et al , 2006 ) . however , in spite of the fact that molluscs are one of the earliest taxa used to investigate latitudinal trends in marine biodiversity , some doubts exist as to whether the latitudinal trends observed in the northern hemisphere also occur in the southern hemisphere ( crame , 2000 ; valdovinos et al , 2003 ; linse et al , 2006 ) . some results are conflicting . for example , the patterns found for pacific ocean molluscs in the southern hemisphere by valdovinos et al . ( 2003 ) opposed those found by fortes & absalão ( 2004 ) .

the present study aimed to investigate patterns in both the regional and depth distribution of gastropod molluscs , discussing aspects of slope and shelf diversity and provinciality , contributing to the discussion about the latitudinal diversity gradient in the southern hemisphere .

the study area comprised the slope and continental shelf between 18° - 23°s and 38° - 41°w , encompassing an area ranging from the abrolhos reef bank , situated in the north of doce river , to the offshore and near - shore region in the vicinity of the paraíba do sul river . the study area was divided into two regions : north ( 18° - 19°s ) , up to 200 km - long , and south ( 21 o - 23°s ) , where the shelf is narrow and shallow , ranging from 10 to 30 km in width ( fig . 1 ) . the continental slope in both regions is narrow and steep ( emery & uchuoi , 1984 ) . the oceanographic conditions consist of oligotrophic area s that are associated with the tropical waters of the brazil current ( bc ) and mesotrophic area s due to the seasonal upwelling of the cold , nutri - ent - rich waters of the south atlantic central water ( sacw ) south of the doce river ( 20°s ) ( valentín et al , 1987 ) . primary productivity varíes from 0 . 3 g c m - 2 d - 1 to 1 . 1 g c m - 2 d - 1 ( gaeta et al , 1999 ) and the input of the doce and paraíba do sul rivers is about 900 m s " . the grain - size distribution is not uniform in the area , varying with depth ; shallower stations have coarse sediments and deeper stations have finer sedi - ments . the clay and silt concentrations revealed a depth gradient as well , with higher concentrations occurring at deeper stations . concentration of calcium carbonate exhibited a patchy distribution , with higher percentages in the western sector ( soares - gomes et al , 1999 ) .

data for this study were obtained in april 1995 , dur - ing the joint oceanographic project ( jops - ii / leg 8 ) , on board the r / v victor hansen from bremen uni - versity , germany . sampling was carried out at 41 stations , between the depths of 20 m and 1 , 330 m ( fig . 1 and table 1 ) . molluscs were present in 37 of these 41 stations ( 23 stations in the shelf zone and 14 in the slope zone ) . the sediment was sampled in triplicate with a 0 . 1 m 2 van veen grab and a 60 x 60 x 30 cm box - corer . samples were standardized to an area of 0 . 1 m and 10 l of sediment volume . the macrozoo - benthos was sieved out with a 0 . 5 mm mesh size , fixed in 70 % ethanol , and sorted under a stereomicro - scope for taxonomic identification .

the frequency of occurrence ( f o = number of oc - currences of a species at the shelf or slope stations / total number of shelf or slope stations ) was calculated , and species were classified according to their value as constant ( f o > 50 % ) , common ( 10 % ≤f o ≤50 % ) , or rare ( f o < 10 % ) . species distribution over the shelf and slope was examined by plotting a histogram of the number of species against the number of stations oc - cupied .

we used estimates 6 . obi software ( colwell , 1997 ) to determine whether the species were classified as " unique " ( restricted to a single site ) , " duplicates " ( occurring at exactly two sites ) , " singletons " ( represented by a single individual ) , or " doubletons " ( represented by only two individuáis ) , following the terminology of colwell & coddington ( 1994 ) .

to perform a species richness scale analysis , the total data set was divided into four regions according to their location in geographic area s ( north and south ) and bathymetric zones ( shelf and slope ) : north shelf , south shelf , north slope , and south slope . due to dif - ferent sampling efforts , randomized species cumula - tives curves were plotted using primer 6 . 1 . 6 software . thus , we were able to compare species richness among regions , where the y - axis is the cumulative number of species and the x - axis the station numbers ( north shelf : 17 , south shelf ; 6 , north slope : 5 , south slope : 9 ) . an area of 0 . 1 m 2 was considered for each sampling station . according to gray ( 2002 ) , when sample sizes are different , this method is preferable to rarefaction curves as proposed by sanders ( 1968 ) . species diversity was also estimated on a progressive spatial scale , according to gray ' s terminology ( 2000 ) : sample species richness ( sr s ) and species richness in large area s ( north shelf , south shelf , north slope , south slope ) ( sr l ) . together , the four regions comprised the total area species richness ( sr t ) . in order to calcúlate the proportion by which a given region is richer than the average of samples within the total area , whittaker ' s ( 1972 ) original beta diversity measure ( ß w = ( γ / α ) - 1 ) was used , where γ is the total number of species resulting from merging a number of individual samples and α is the average number of species per individual sample . beta diversity was measured over sectors [ ß w = ( sr l / mean sr s ) ] and total area [ ß w = ( sr t / mean sr s ) ] scales , where mean nsr s was the mean sample diversity .

the species ' geographic and bathymetric distribution ranges were determined based on information available in the literature ( abbott , 1974 ; merlano & hegedus , 1994 ; rios , 1994 , among others ) and in the malacolog 3 . 1 electronic database ( rosenberg , 1993 - urltoken ) . geographic boundaries were established based on the south - western atlantic biogeographic provinces ( tropical , paulista , patagonic , malvinas ) defined by palacio ( 1982 ) using the endemism rate . for a better representation of the geographic distribution in the area , the species were grouped according to their occurrence in the north and south regions . the shelf samples provided 211 species : 91 from the south region , 179 from the north region , and 59 from both regions . from the slope samples , 96 species were used : 72 from the south region , 55 from the north , and 31 from both regions . depending on the bathymetric distribution , species were designated according to the zonation proposed by zezina ( 1997 ) and vinogradova ( 1997 ) as : shallow species ( 0 - 200 m depth ) , bathyal species ( 200 - 3 , 000 m ) , and abyssal species ( 3 , 000 - 6 , 000 m ) . species found in both the shelf and bathyal zones were designated eurybathic .

we excluded pelagic species and juveniles ( 12 . 25 % of the total number of species ) from the analyses due , not only to the difficulties in identifying juveniles , but also to the aim of the present study , which is to analyze only benthic species . only individuáis identified to the species level or ones that could unequivocally be labelled as species were used in the analysis .

a total of 9 , 845 specimens , 404 species and morpho - types ( including empty shells ) , 189 genera , and 73 families were collected over the entire study area . a set of 243 species , 93 genera , and 28 families was found exclusively in the shelf zone , whereas 137 species , 43 genera , and 14 families were exclusive to the slope zone . only 24 species ( 6 % ) , 20 genera ( 10 . 6 % ) , and 16 families ( 22 % ) occurred in both zones ( appendix 1 and 2 ) .

species distribution over the shelf shows that about half the species ( 130 ) were restricted to one station and none occurred at all stations . the same pattern was found for the slope , with 110 species restricted to one single site . considering the shelf and slope , about 3 % of the species occurred at more than 50 % of all sites ( fig . 2 ) . on the shelf , 2 % were constant , 32 % common , and 66 % rare species . on the slope , the corresponding figures were 1 % , 42 % , and 57 % .

in the whole area , 48 % of the species were unique and 18 % were duplicates . singletons and doubletons represented 34 % and 13 % , correspondingly . the north shelf featured 26 % unique species and 17 % singletons , and the north slope had 12 % unique species and 5 % singletons ( table 2 ) .

the cumulative dominance on the shelf was similar for both north and south regions . on the slope , there was a great difference in cumulative dominance be - tween the two regions , with the north presenting the highest evenness ( fig . 3 ) . comparing the cumulative dominance along a vertical gradient , the evenness of the north slope was almost 10 % higher than that of the north shelf , whereas the evenness of the south shelf was 40 % higher than that of the south slope ( fig . 3 ) .

the estimated species richness on the north shelf was higher than on the south shelf . however , when the sampling area was standardized to 0 . 6 m 2 ( considering the area of a station as 0 . 1 m 2 , ) , the richness was similar on both shelves ( fig . 4 ) . the south slope displayed a higher total cumulative number of species per area than did the north slope . conversely , when standardizing the sampling area to 0 . 5 m 2 , richness was higher on the north slope . in the north , species richness was 0 . 5 m 2 higher in the slope zone than in the shelf zone , whereas the opposite pattern was observed in the south ( fig . 4 ) .

in terms of diversity scales , the alpha diversity ( sr s ) values found in the study area ranged from 2 to 84 species . the mean alpha diversity was highest on the north shelf , where 84 species were found at one station , followed by the south shelf , where richness ranged from 15 to 43 species within stations . the highest value of beta diversity ( sr l / means sr s ) was found on the north shelf ( 6 . 66 ) and the lowest on the north slope ( 3 . 22 ) . ß w values almost doubled on the largest scale ( sr t / means sr s ) compared to the highest value found on the large area scale ( table 2 ) .

appendix 1 . taxonomic list of species from the continental shelf ( 25 - 200 m depth ) .

apéndice 1 . lista taxonómica de especies de la plataforma continental ( 25 - 200 m de profundidad ) .

appendix 2 . taxonomic list of species from the continental slope ( 300 - 1330 m depth ) .

apéndice 2 . lista taxonómica de especies de la plataforma continental ( 300 - 1330 m de profundidad ) .

bulla " aff . " abyssicola dalí , 1881 bulla " aff . " ebúrnea ( dalí , 1881 )

for the continental shelf samples , 211 species and 89 genera were characterized according to their occur - rence in the southwestem atlantic zoogeographic provinces : 91 species from the south , 179 from the north , and 59 species from both regions . for the continental slope samples , 96 species and 52 genera were characterized : 72 species from the south , 55 from the north , and 31 from both regions .

in terms of the geographical distribution of taxa , the number of genera with a wide distributional range ( occurring in more than three provinces ) was lower than the genera with narrower distributions for both shelf and slope stations . however , considering the genera that occurred in both zones , the number of wide - range distributions was higher than the narrow - range ones ( table 3 ) .

at the shelf stations , the number of species co - occurring in both tropical and paulista ( tropical - paulista species ) provinces was greater than the number of tropical species occurring in both regions . in addition , the number of tropical , paulista , and tropi - cal - paulista species decreased and the number of wide - distribution eurythermic species increased in the southwestem atlantic provinces ( tropical - paulista - patagonic species ) towards the south ( fig . 5 ) . at the slope stations , tropical species were the majority in both regions . the number of tropical , paulista , tropi - cal - paulista , tropical - paulista - patagonic , and subtropical paulista - patagonic species increased towards the south . the number of endemic species was higher in the north for both shelf and slope stations . in addi - tion , a greater number of tropical endemic species was present at the slope stations in both the south and north , and the shelf stations displayed the highest occurrence of paulista endemic species . the number of species occurring in all western atlantic provinces was greater on the south shelf ( table 4 ) . furthermore , shelf stations showed a higher number of eurybathic species ( with a wide bathymetrical range ) than did slope stations ( table 5 ) .

the shelf - slope transition zone is known to have a high species turnover rate ( rex et al , 1977 ) . more - over , species typically found on continental shelves and species from continental slope zones can coexist there , leading to higher species richness . however , evidence from studies done on the brazilian continental slope showed that the depth where this species turnover begins is variable . in this study , we found high species turnover at station 16 ( 300 m depth ) , where some deep - sea species , such as alvania xantias ( watson , 1885 ) , brookula spinulata ( absalão , miyaji & pimenta , 2001 ) , and solariella lubrica ( dalí , 1881 ) showed a high dominance . miyaji ( 2001 ) found a rough change , with 8 % of sampled species occurring exclusively at depths greater than 400 m , whereas sumida & pires - vanin ( 1997 ) found a different com - munity from shallow area s occurring between 320 m and 500 m depth .

analyzing the vertical distribution of species found in this study ( table 2 ) , we observed the occurrence of shallow - water and eurybathic species ( shallow - bathyal , shallow - bathyal - abyssal , bathyal - abyssal distributions ) at the slope stations . this pattern might constitute evidence of the slope ' s capacity to allow the co - existence of shallow and deep - water species .

the depth gradient differed between the north and south regions : the north shelf showed the highest local , regional , and between - habitat species richness , whereas the south slope had the highest species richness , with values cióse to the shelf ones . along local gradients , the general pattern observed is that species richness changes with depth , increasing from ca . 200 m to 1500 - 2500 m or more , and then decreasing towards the abyssal plain ( rex et al , 1993 , 2000 ; gray , 2002 ) . nevertheless , those unimodal patterns do not appear to be universal ( rex et al , 1997 ; stuart et al , 2001 ) , showing that the change in species richness is not related to depth itself ( gray , 2002 ) .

in addition to the above - mentioned patterns , environmental features also changed with depth . both north and south slopes are narrow and steep , with more homogeneous bottoms that are dominated by silt fractions and a higher concentration of organic carbon .

the disappearance of some tropical species towards the south suggests that the southernmost limit of the tropical province is located cióse to 21°s , ac - cording to the results found for gastropods ( floeter & soares - gomes , 1999 ) ; cirripeds ( young , 1995 ) , and polychaetes ( lana , 1987 ) . nevertheless , the location of that limit remains uncertain ( absalão , 1989 ; mello , 1993 ; briggs , 1995 ) . recently , joyeux et al . ( 2001 ) and floeter et al . ( 2008 ) found that , for tropical reef fishes , the southern limit is 28°s .

many studies have demonstrated that the bounda - ries of shallow - water faunal distribution are correlated to water masses boundaries ( stevenson et al , 1998 ; culver & buzas , 2000 ) . the presence of species with tropical affinities over the shelf area could be ex - plained by the predominance of the warm and saline water mass of the brazil current ( bc ) ( absalão , 1989 ; miyaji , 1995 , 2001 ) that flows southwards ( parallel to the shelf break ) to 35°s ( emilsson , 1961 ) . in that region , the bc mixes with the cold and less saline water mass of the malvina current and the water character - istics become markedly subtropical , with salinity and temperature ranging between 36 - 35 and 20° - 10°c , respectively ( emilsson , 1961 ) . this fact influences the occurrence of cold - water affinity species ( semenov & berman , 1977 ; palacio , 1982 ) .

however , the most significant factor for the main - tenance of cold - water species , as well as of eurybathic species in the shelf zone , particularly in the north region , might be the penetration of the south atlantic central water ( sacw ) into the continental shelf re - gions . this water mass acts as a vehicle for larval dispersal from cold , deeper regions to warm , shal - lower area s ( absalão , 1989 ; miyaji , 1995 , 2001 ) , and extends northwards to espirito santo state ( gaeta et al , 1999 ) .

important changes occur in the benthic faunal structure within the large vertical interval of the bathyal zone . the most obvious difference between shallow and deep - bottoms is the reduction in the number of latitudinal or climatic belts , both in terms of biomass and of faunal structures ( zezina , 1997 ) . as there is a simplification in the water mass structure of the continental slope floor region , a reduction in the number of faunal provinces is to be expected ( semenov & berman , 1977 ; zezina , 1997 ; culver & buzas , 2000 ) . culver & buzas ( 2000 ) found that the differences in benthic foraminifera fauna between shallow ( < 200 m ) and deep water ( > 200 m ) provinces at the same latitude were greater than between adjacent shallow water provinces .

as expected , species occurring in the shelf zone were very distinct from those in the slope area , with only 24 ( out of 315 ) species shared between the two zones . when the latitudinal distribution of slope species is analyzed , the pattern is similar to the shelf species distribution . however , the number of tropical and tropical - paulista species increased in the south region .

studies on geographical distributions of deep - sea species have shown a greater number of species with wider horizontal ranges ( vinogradova , 1997 ; zezina , 1997 ) . however , the present study found few species with wide range distributions towards the slope sta - tions . similar results were observed for the geographic distribution of genera . the restricted - range genera ( 1 to 2 provinces ) were represented by six more genera than the wide - range ones ( > 2 provinces ) . it is , however , possible that the lower number of samples for the slope region ( 14 stations vs . 23 in the shelf zone ) might induce such contradictory results . it is expected that enhanced sampling efforts will not only tend to increase the more sparsely distributed species , but also the number of " rare " endemic species ( alien & sand - ers , 1996 ) .

zezina ( 1997 ) proposed biogeographic schemes for the bathyal zone based on a recent brachiopod distribution , which is very similar to the results found in the present study for gastropods firom the continental slope . this scheme proposed , for depths greater than 700 m in the northeast and central brazilian bathyal zone ( similar to the schemes for shallow - water fauna in the southwestern atlantic ) , a sub - area named the atlantic - central american ( divided into caribbean and brazilian provinces ) and the south brazilian - uruguayan subtropical area in the southeast and south bathyal zones . also , for recent brachiopods living below 700 m , zezina ( 1997 ) defined only one area for the entire southwestern atlantic ocean : the amphi - atlantic bathyal area within the central atlantic province .

a great species turnover rate was observed between the shelf and slope . an analysis of the gastro - pod species distribution revealed a similar pattern of regional distribution in shelf and slope zones and a great difference between shallow and deep - water faunas . although the present analysis of biogeographic distribution patterns confirmed the existence of a transitional zone firom tropical to subtropical waters in the case of the slope zone , the sampling effort done on the southeastern atlantic slope is still too little and those results should be viewed with caution .

the authors are indebted to dr . bastian knoppers for the invitation to join in the joint oceanographic project ii ( jops - ii ) , and to drs . ricardo silva absalão and paulo márcio costa for helping with taxonomic identification . we also thank dr . sergio floeter for some valuable suggestions that improved the manuscript and carla mendes for reviewing the english version .

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