''Pisidium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of very small or minute

freshwater clam Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails. The majority of bivalve molluscs are saltwater species that liv ...

s known as pill clams or pea clams,

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Sphaeriidae Sphaeriidae is a family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, ...

, 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 language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...

). 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 (), also hadrosaurs 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 fami ...

eggshell An eggshell is the outer covering of a hard-shelled egg (biology), egg and of some forms of eggs with soft outer coats. 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 Precipitation (chemistry), precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widel ...

s from the local

coniferous Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

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 Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

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 ''Pisidium moitessierianum'' is a species of small freshwater clam. It is an aquatic bivalve mollusc in the family Sphaeriidae. Description This species is the smallest of the pea clams or ''Pisidium'' species, and the smallest of any fresh ...

'' 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. T ...

'' (Poli, 1791) *''

Pisidium globulare ''Pisidium globulare'' is a species of freshwater bivalve from the family Sphaeriidae. Distribution * Czech Republic – in Bohemia, in Moravia Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. (2010). "Komentovaný seznam měkkýš ...

'' Clessin, 1873 *''

Pisidium personatum ''Pisidium personatum'' is a species of freshwater bivalve from the family Sphaeriidae. Description The 2.5-3.5 mm shell is a characteristic round-regular oval shape. It has centrally placed low, rounded umbos. The surface (periostracum) is ...

'' 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&n ...

'' (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 organi ...

'' Westerlund, 1897 Subgenus ''Cyclocalyx'' Dall, 1903 *''

Pisidium hinzi ''Euglesa hinzi'' is a species of mollusc belonging to the family Sphaeriidae. It is native to Northern Europe. Synonym: * ''Pisidium hinzi'' Kuiper, 1975 (= basionym In the scientific name of organisms, basionym or basyonym means the original ...

'' 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 (perio ...

'' (

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 biolo ...

, 1818) Subgenus ''Tropidocyclas'' Dall, 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 Henslow. ...

'' (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 small 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 in ...

'' A. Schmidt, 1851 *''

Pisidium waldeni ''Euglesa waldeni'' is a species of mollusc belonging to the family Sphaeriidae. It is native to Northern Europe. Synonym: * ''Pisidium waldeni'' Kuiper, 1975 (= basionym In the scientific name of organisms, basionym or basyonym means the orig ...

'' Kuiper, 1975 Subgenus ''Hiberneuglesa'' Starobogatov, 1983 *''

Pisidium hibernicum ''Pisidium hibernicum'' is a species of freshwater bivalve from the family Sphaeriidae. Description The 2.5-3.5mm. shell is very inflated (convex) hence the common name Globular Pea Shell. The central umbos is prominent. The periostracum (surfa ...

'' Westerlund, 1894 Subgenus ''Cingulipisidium'' Pirogov & Starobogatov, 1974 *'' Pisidium crassum'' Stelfox, 1918 *'' Pisidium milium'' Held, 1836 *'' Pisidium nitidum'' Jenyns, 1832 *''

Pisidium pseudosphaerium ''Pisidium pseudosphaerium'' is a species of freshwater bivalve from family Sphaeriidae. Description The 2.5-3.2mm shell is a flattened, regular, slightly angulated oval shape with low central umbos. The surface is silky with very fine concentri ...

'' Favre, 1927 Subgenus ''Pseudeupera'' Germain, 1909 *'' Pisidium pulchellum'' Jenyns, 1832 *'' Pisidium subtruncatum'' Malm, 1855 Subgenus ''Neopisidium'' Odhner, 1921 *'' Pisidium conventus'' Clessin, 1867 Subgenus ''Odhneripisidium'' Kuiper, 1962 *''

'' Paladilhe, 1866 *''

Pisidium tenuilineatum ''Pisidium tenuilineatum'', the fine-lined pea mussel, is a species of very small freshwater bivalve in the family Sphaeriidae. Distribution The species is native to Europe. * British Isles – listed in List of endangered species in the Briti ...

'' Stelfox, 1918 Subgenus ''Afropisidium'' Kuiper, 1962 *'' Pisidium giraudi'' Bourguignat, 1885 *'' Pisidium hodgkini'' (

Suter Suter is a surname. Notable people with the name include: * Alexis P. Suter (born 1963), American blues, and soul blues singer and songwriter * Andrew Burn Suter (1830–1895), Bishop of the Diocese of Nelson, New Zealand * Andrina Suter (bor ...

, 1905) *'' Pisidium pirothi'' Jickeli, 1881 Subgenus unknown *'' Pisidium artifex'' Kuiper, 1960 *''

Pisidium stewarti ''Pisidium stewarti'' is a species of small 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 Pleistocene g ...

'' Preston, 1909 Subgenus ' *'' Pisidium annandalei'' Prashad, 1925 *'' Pisidium edlaueri'' Kuiper, 1960 *'' Pisidium javanum'' 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 {{Authority control Bivalve genera