''Pisidium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of very small or minute freshwater clams known as pill clams or pea clams, aquatic

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

molluscs in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

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.

''Pisidium'' and 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 Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremo ...

). For example, in the

Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 7 ...

, the fossil remains of

hadrosaur Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...

eggshell An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats. Diversity Worm eggs Nematode eggs present a two layered structure: an external vitellin layer made of chitin that confers mechanical ...

s are rare. This is because the breakdown of

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner ...

s 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. Hadrosaur eggshell fragments are however present in two

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

sites in the area. Both of these sites are dominated by preserved shells of invertebrate life, primarily shells of pisidiids. 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. 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.''

Extant subgenera and species

Extant subgenera and species within the genus ''Pisidium'' include: Subgenus ''Euglesa'' Jenyns, 1832 *''

Pisidium casertanum ''Pisidium casertanum'', the pea cockle or pea clam, is a minute freshwater bivalve mollusc of the family Sphaeriidae. Description The shell is broad, sub-triangular or oval and is ornamented with sculpture of faint concentric striations. ...

'' (Poli, 1791) *'' Pisidium globulare'' Clessin, 1873 *'' Pisidium personatum'' Malm, 1855 Subgenus ''Pisidium'' Pfeiffer, 1821 *''

Pisidium amnicum ''Pisidium amnicum'' is a species of very small freshwater clam, sometimes known as the greater European peaclam or the River pea shell. It is an aquatic bivalve in the family Sphaeriidae. Description Although only 9 mm (range 7–11& ...

'' (O. F. Müller, 1774) *''

Pisidium dilatatum ''Pisidium dilatatum'' is a species of freshwater bivalve belonging to the family Sphaeriidae. It is widespread in Europe and Asia, from southern Sweden in the west to Lake Baikal in the east. It occurs in oligotrophic An oligotroph is an organ ...

'' Westerlund, 1897 Subgenus ''Cyclocalyx''

Dall Dall may refer to: People * Anders Bendssøn Dall (died 1607), Danish Lutheran bishop * Bobby Dall (born 1963), American musician * Caroline Healey Dall (1822–1912), American feminist writer *Clarrie Dall (1887–1953), Australian footballer * C ...

, 1903 *'' Pisidium hinzi'' Kuiper, 1975 *''

Pisidium obtusale ''Pisidium obtusale'' is a species of freshwater bivalve from family Sphaeriidae. Description The 2.5–3.5mm. shell is very tumid (swollen). It is an angular-oval shape with broad, rounded umbos which are behind the midpoint. The surface (peri ...

'' (

Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biolog ...

, 1818) Subgenus ''Tropidocyclas''

, 1903 *''

Pisidium henslowanum ''Pisidium henslowanum'' is a species of very small freshwater clam or pea clam, an aquatic bivalve mollusc in the family Sphaeriidae. It is commonly referred to as the Henslow peaclam. Etymology The specific name honours John Stevens Henslo ...

'' (Sheppard, 1823) *''

Pisidium lilljeborgii ''Pisidium lilljeborgii'' is a species of freshwater bivalve from the family Sphaeriidae. Description A moderately swollen (tumid), trapezoidal shell. The umbos are just behind the mid point and described as fairly narrow. The surface (periostra ...

'' Clessin, 1886 *''

Pisidium supinum ''Pisidium supinum'' is a species of minute freshwater clam, a pea clam, an aquatic bivalve mollusc in the family Sphaeriidae (the fingernail clams and pea clams.) The shell of this species is 3 to 5 mm in size, and is roughly triangular ...

'' A. Schmidt, 1851 *'' Pisidium waldeni'' Kuiper, 1975 Subgenus ''Hiberneuglesa'' Starobogatov, 1983 *'' Pisidium hibernicum'' Westerlund, 1894 Subgenus ''Cingulipisidium'' Pirogov & Starobogatov, 1974 *''

Pisidium crassum ''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 S ...

'' Stelfox, 1918 *''

Pisidium milium ''Pisidium milium'' is a species of very small freshwater bivalve in the family Sphaeriidae, the fingernail clams and pea clams. Description The 3.0- to 4.5-mm shell is tumid (swollen). It is more rectangular than other ''Pisidium'' specie ...

'' Held, 1836 *'' Pisidium nitidum'' Jenyns, 1832 *'' Pisidium pseudosphaerium'' Favre, 1927 Subgenus ''Pseudeupera'' Germain, 1909 *''

Pisidium pulchellum ''Pisidium pulchellum'' , the iridescent pea mussel, is a minute species of pea clam, a freshwater bivalve in the family Sphaeriidae. Description The 3.5–4 mm shell is tumid (swollen), oblique-oval shell. The umbos are broad well and w ...

'' Jenyns, 1832 *''

Pisidium subtruncatum ''Pisidium subtruncatum'' is a species of pill clam, a minute freshwater bivalve in the family Sphaeriidae. Description The 2.7 – 4 mm shell is moderately tumid (swollen). In shape it is a strongly oblique oval. The umbos are prominen ...

'' Malm, 1855 Subgenus ''Neopisidium'' Odhner, 1921 *''

Pisidium conventus ''Pisidium conventus'', the arctic-alpine pea clam, is a species of freshwater bivalve from the family Sphaeriidae. Description The small (2.2–2.8 mm.) shell is oval in shape and thin and fragile. It is broad and flattened (laterally com ...

'' Clessin, 1867 Subgenus ''Odhneripisidium'' Kuiper, 1962 *'' Pisidium moitessierianum'' Paladilhe, 1866 *'' Pisidium tenuilineatum'' Stelfox, 1918 Subgenus ''Afropisidium'' Kuiper, 1962 *'' Pisidium giraudi'' Bourguignat, 1885 *''

Pisidium hodgkini ''Pisidium hodgkini'' is a freshwater bivalve of the family Sphaeriidae, which is found in New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North ...

'' ( Suter, 1905) *''

Pisidium pirothi ''Afropisidium pirothi'' is a species of bivalve belonging to the family Sphaeriidae. The species is found in Africa. References

Sphaeriidae Bivalves described in 1881 Bivalves of Africa {{Sphaeriidae-stub ...

'' Jickeli, 1881 Subgenus unknown *''

Pisidium artifex ''Pisidium artifex'' is a species of freshwater clam in the family Sphaeriidae. It is endemic to Kenya, where it is known only from Mount Kenya Mount Kenya (Kikuyu: ''Kĩrĩnyaga'', Kamba, ''Ki Nyaa'') is the highest mountain in Kenya and t ...

'' Kuiper, 1960 *''

Pisidium stewarti ''Pisidium stewarti'' is a species of minute freshwater clam. It is an aquatic bivalve mollusc in the family Sphaeriidae, the fingernail clams and pea clams. Distribution This minute clam, which is known in Europe as a decidedly Pleistoce ...

'' Preston, 1909 Subgenus ' *''

Pisidium annandalei ''Pisidium'' is a genera, genus of very small or minute freshwater clams known as pill clams or pea clams, Aquatic animal, aquatic bivalve molluscs in the family (biology), family Sphaeriidae, the pea clams and fingernail clams. In some bivalv ...

'' Prashad, 1925 *''

Pisidium edlaueri ''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 Spha ...

'' Kuiper, 1960 *''

Pisidium javanum ''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 S ...

'' van Benthem Jutting, 1931 *'' Pisidium maasseni'' Kuiper, 1987 *'' Pisidium punctiferum'' (Guppy, 1867) *'' Pisidium raddei'' Dybowski, 1902 * undescribed ''Pisidium'' species from Africa (Kuiper, in prep., awaiting additional records)Kuiper J.G.J. (2009). "Fossil records of Palaearctic ''Pisidium'' species in tropical Africa". Zoologische Mededelingen 83(10): 593-594
HTM
.

Footnotes

References

* 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

''Pisidium''
keyed, described and illustrated in ''Danmarks Fauna'' (Georg Mandahl-Barth)
''Pisidium'' images
at

Consortium for the Barcode of Life The Consortium for the Barcode of Life (CBOL) was an international initiative dedicated to supporting the development of DNA barcoding as a global standard for species identification. CBOL's Secretariat Office is hosted by the National Museum of ...

* https://web.archive.org/web/20141128091542/http://sunsite.ualberta.ca/Projects/Aquatic_Invertebrates/?Page=20 {{Taxonbar, from=Q600521 Bivalve genera