{{Short description|Genus of bivalves}} {{Use dmy dates|date=January 2022}} {{Automatic taxobox | taxon = Pisidium | image = Pisidium pseudosphaerium.png | image_caption = External view of the left valve of ''Pisidium pseudosphaerium'' | authority = C. Pfeiffer, 1821 | display_parents = 3 | type_species = Pisidium amnicum | type_species_authority = (O. F. Müller, 1774) | subdivision_ranks = Species | subdivision = See text | synonyms = {{collapsible list| *''Pisidium (Pisidium)'' C. Pfeiffer, 1821 *''Corneocyclas (Pisidium)'' C. Pfeiffer, 1821 *''Cyclas (Pisidium)'' C. Pfeiffer, 1821 *''Cyrena (Pisidium)'' C. Pfeiffer, 1821 *''Pera'' Leach, 1831 *''Cordula'' Leach, 1852 *''Pisidium (Fluminina)'' Clessin, 1873 *''Amniciana'' Servain, 1888 *''Pisidium (Amniciana)'' Servain, 1888 *''Lacustrina'' Sterki, 1916 *''Pisidium (Lacustrina)'' Sterki, 1916 *''Pisidium (Parapisidium)'' Kuiper, 1966 *''Pisidium (Amuropisidium)'' Prozorova, 1995}} |synonyms_ref = <ref name=WoRMS/> }}
'''''Pisidium''''' is a genus of very small or minute freshwater clams known as pill clams or pea clams, aquatic bivalve molluscs in the family Sphaeriidae, the pea clams and fingernail clams.
In some bivalve classification systems, the family Sphaeriidae is referred to as Pisidiidae, and occasionally ''Pisidium'' species are grouped in a subfamily known as Pisidiinae.
==Taphonomy== In large enough quantities, the minute shells of these bivalves can affect environmental conditions, and this change in conditions can positively affect the ability of organic remains in the immediate environment to fossilize (one aspect of taphonomy).<ref name="tanke-brett-surman-2001" /> For example, in the Dinosaur Park Formation, the fossil remains of hadrosaur eggshells are rare.<ref name="hadro-egg-abs-206" /> This is because the breakdown of tannins from the local coniferous vegetation caused the ancient waters to be acidic, and therefore usually eggshell fragments dissolved in the water before they had a chance to be fossilized.<ref name="hadro-egg-disc-212" />
Hadrosaur eggshell fragments are however present in two microfossil sites in the area. Both of these sites are dominated by preserved shells of invertebrate life, primarily shells of pisidiids.<ref name="hadro-egg-abs-206" /> The slow dissolution of these minute bivalve shells released calcium carbonate into the water, raising the water's pH high enough that it prevented the hadrosaur eggshell fragments from dissolving before they could be fossilized.<ref name="hadro-egg-shell-209" /> <gallery>Image:Pisidium moitessierianum.svg|Drawing of the right valve external view of ''Pisidium moitessierianum'' Image:Pisidium moitessierianum 3.svg|Drawing of the right valve internal view of ''Pisidium moitessierianum'' Image:Pisidium moitessierianum 2.svg|Drawing of the right valve lateral view of ''Pisidium moitessierianum'' Image:Pisidium sp.jpg|SEM image of ''Pisidium sp.''</gallery>
==Extant subgenera and species== Extant <!--subgenera and (find sources corroborating the subgenera)-->species within the genus ''Pisidium'' include:<ref name=WoRMS>{{Cite WoRMS|title=Pisidium C. Pfeiffer, 1821|id=181554|access-date=2026-02-11|db=MolluscaBase}}</ref> {{Div col|colwidth=24em}} *''Pisidium amnicum'' (O. F. Müller, 1774) *''Pisidium amurense'' Moskvicheva, 1985 *''Pisidium armillatum'' Kuiper, 1966 *''Pisidium artifex'' Kuiper, 1960 *''Pisidium baicalense'' W. Dybowski, 1902 *''Pisidium bejumae'' H. B. Baker, 1930 *''Pisidium betafoense'' Kuiper, 1953 *''Pisidium boliviense'' Sturany, 1900 *''Pisidium chicha'' Ituarte, 2005 *''Pisidium chiquitanum'' Ituarte, 2001 *''Pisidium cruciatum'' Sterki, 1895 *''Pisidium decurtatum'' Lindholm, 1909 *''Pisidium dilatatum'' Westerlund, 1897 *''Pisidium dorbignyi'' Clessin, 1877 *''Pisidium dubium'' (Say, 1817) *''Pisidium fistulosum'' Mandahl-Barth, 1954 *''Pisidium forense'' Meier-Brook, 1967 *''Pisidium globulus'' Clessin, 1888 *''Pisidium habbemae'' Odhner, 1940 *''Pisidium huillichum'' Ituarte, 1999 *''Pisidium idahoense'' E. W. Roper, 1890 *''Pisidium inacayali'' Ituarte, 1996 *''Pisidium inflexum'' Odhner, 1940 *''Pisidium invenustum'' Kuiper, 1966 *''Pisidium iquito'' Ituarte, 2004 *''Pisidium jamaicense'' Prime, 1865 *''Pisidium johnsoni'' E. A. Smith, 1882 *''Pisidium lebruni'' Mabille, 1884 *''Pisidium llanquihuense'' Ituarte, 1999 *''Pisidium magellanicum'' (Dall, 1908) *''Pisidium meierbrooki'' Kuiper & Hinz, 1984 *''Pisidium montigenum'' Kuiper, 1966 *''Pisidium observationis'' Pilsbry, 1911 *''Pisidium ocloya'' Ituarte, 2005 *''Pisidium omaguaca'' Ituarte, 2005 *''Pisidium orientale'' Prozorova, 1995 *''Pisidium patagonicum'' Pilsbry, 1911 *''Pisidium pipoense'' Ituarte, 2000 *''Pisidium plenilunium'' (Melvill & Standen, 1907) *''Pisidium punctatum'' Sterki, 1895 *''Pisidium punctiferum'' (Guppy, 1867) *''Pisidium reticulatum'' Kuiper, 1966 *''Pisidium sanguinichristi'' D. W. Taylor, 1987 *''Pisidium sterkianum'' Pilsbry, 1897 *''Pisidium taraguyense'' Ituarte, 2000 *''Pisidium vile'' Pilsbry, 1897 *''Pisidium volutabundum'' Vanatta, 1910 *''Pisidium wilhelminae'' Odhner, 1940 {{Div col end}}
The following species require evaluation to confirm their placement in ''Pisidium''; many of the following are ''taxa inquirenda'' and have not been used by recent authors:<ref name=WoRMS/> {{Div col|colwidth=24em}} *''Pisidium acuminatum'' Clessin, 1874 *''Pisidium acutum'' L. Pfeiffer, 1841 *''Pisidium alienum'' Clessin, 1879 *''Pisidium bartolomeum'' Clessin, 1873 *''Pisidium colbeuai'' Clessin, 1875 *''Pisidium costatum'' Sterki, 1903 *''Pisidium costulatum'' Westerlund, 1898 *''Pisidium demissum'' Clessin, 1876 *''Pisidium duplicatum'' L. Pfeiffer, 1841 *''Pisidium foreli'' Clessin, 1876 *''Pisidium herminii'' Clessin, 1877 *''Pisidium italicum'' Clessin, 1875 *''Pisidium marteli'' Pallary, 1928 *''Pisidium miliolum'' Clessin, 1907 *''Pisidium moreanum'' Clessin, 1874 *''Pisidium obliquum'' L. Pfeiffer, 1841 *''Pisidium obtusale'' (Lamarck, 1818) ''sensu'' C. Pfeiffer, 1821 *''Pisidium obtusatum'' Clessin, 1875 *''Pisidium occupatum'' Clessin, 1876 *''Pisidium ovatum'' Clessin, 1877 *''Pisidium persicum'' Prashad, 1933 *''Pisidium pileus'' Clessin, 1873 *''Pisidium profundum'' Clessin, 1876 *''Pisidium rotundatum'' Pallary, 1922 *''Pisidium schmidti'' Clessin, 1907 *''Pisidium shadini'' Johansen, 1937 *''Pisidium sphaeriiforme'' Clessin, 1874 *''Pisidium tumidum'' Clessin, 1875 *''Pisidium watsoni'' Paiva, 1866 *''Pisidium wolfii'' Clessin, 1879 * undescribed ''Pisidium'' species from Africa (Kuiper, in prep., awaiting additional records)<ref>Kuiper J.G.J. (2009). "Fossil records of Palaearctic ''Pisidium'' species in tropical Africa". Zoologische Mededelingen '''83'''(10): 593-594. [http://www.zoologischemededelingen.nl/83/nr03/a10 HTM] {{Webarchive|url=https://web.archive.org/web/20160304033139/http://www.zoologischemededelingen.nl/83/nr03/a10 |date=4 March 2016 }}.</ref> {{Div col end}} The genera ''Conventus'', ''Euglesa'', ''Hindupisidium'', ''Odhneripisidium'', and ''Sphaerium'' were split out from ''Pisidium'' after taxonomic revision.<ref name=WoRMS/>
==Footnotes== {{Reflist|refs= <ref name="tanke-brett-surman-2001">Tanke and Brett-Surman (2001).</ref> <ref name="hadro-egg-abs-206">"Abstract," Tanke and Brett-Surman (2001). Page 206.</ref> <ref name="hadro-egg-disc-212">"Discussion," Tanke and Brett-Surman (2001). Page 212.</ref> <ref name="hadro-egg-shell-209">"Eggshell," Tanke and Brett-Surman (2001). Page 209.</ref> }}
==References== {{reflist}} * Tanke, D.H. and Brett-Surman, M.K. 2001. Evidence of Hatchling and Nestling-Size Hadrosaurs (Reptilia:Ornithischia) from Dinosaur Provincial Park (Dinosaur Park Formation: Campanian), Alberta, Canada. pp. 206–218. In: Mesozoic Vertebrate Life—New Research Inspired by the Paleontology of Philip J. Currie. Edited by D.H. Tanke and K. Carpenter. Indiana University Press: Bloomington. xviii + 577 pp.
==External links== {{Commons category|Pisidium}} *[https://www.biodiversitylibrary.org/page/36123356#page/147/mode/1up ''Pisidium''] keyed, described and illustrated in ''Danmarks Fauna'' (Georg Mandahl-Barth) *[http://www.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=348861 ''Pisidium'' images] at Consortium for the Barcode of Life * https://web.archive.org/web/20141128091542/http://sunsite.ualberta.ca/Projects/Aquatic_Invertebrates/?Page=20
{{Taxonbar|from=Q600521}} {{Authority control}}
Category:Pisidium Category:Bivalve genera