''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 clams known as pill clams or pea clams,
aquatic 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, 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).
For example, in the
Dinosaur Park Formation, the fossil remains of
hadrosaur 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 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.
Extant subgenera and species
Extant subgenera and species within the genus ''Pisidium'' include:
Subgenus ''Euglesa'' Jenyns, 1832
*''
Pisidium casertanum'' (Poli, 1791)
*''
Pisidium globulare'' Clessin, 1873
*''
Pisidium personatum'' Malm, 1855
Subgenus ''Pisidium''
Pfeiffer, 1821
*''
Pisidium amnicum'' (O. F. Müller, 1774)
*''
Pisidium dilatatum'' Westerlund, 1897
Subgenus ''Cyclocalyx''
Dall, 1903
*''
Pisidium hinzi'' Kuiper, 1975
*''
Pisidium obtusale'' (
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'' (Sheppard, 1823)
*''
Pisidium lilljeborgii'' Clessin, 1886
*''
Pisidium supinum'' A. Schmidt, 1851
*''
Pisidium waldeni'' Kuiper, 1975
Subgenus ''Hiberneuglesa'' Starobogatov, 1983
*''
Pisidium hibernicum'' Westerlund, 1894
Subgenus ''Cingulipisidium'' Pirogov & Starobogatov, 1974
*''
Pisidium crassum''
Stelfox, 1918
*''
Pisidium milium'' Held, 1836
*''
Pisidium nitidum'' Jenyns, 1832
*''
Pisidium pseudosphaerium'' 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
*''
Pisidium moitessierianum'' Paladilhe, 1866
*''
Pisidium tenuilineatum''
Stelfox, 1918
Subgenus ''Afropisidium'' Kuiper, 1962
*''
Pisidium giraudi'' Bourguignat, 1885
*''
Pisidium hodgkini'' (
Suter, 1905)
*''
Pisidium pirothi'' Jickeli, 1881
Subgenus unknown
*''
Pisidium artifex'' Kuiper, 1960
*''
Pisidium stewarti'' 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'' imagesat
Consortium for the Barcode of Life
* https://web.archive.org/web/20141128091542/http://sunsite.ualberta.ca/Projects/Aquatic_Invertebrates/?Page=20
{{Authority control
Bivalve genera