Pea Clams
Pea clams are a group of Colorado native, bivalve mollusks.
About This Species
Pea clams are a group of small, freshwater bivalves in the Family Sphaeriidae (sometimes referred to as Family Pisidiidae). They are also known as pill clams or fingernail clams. Genus Pisidium contains many species, all of which are very small and difficult to identify. Existing taxonomy is in flux as research continues. Most pea clams are very small and are difficult to identify without a hand lens. Even with a lens, it is difficult to distinguish one pea-clam species from another and the range of variation due to environment is likely as great within species as is found between some species. In large numbers, these bivalves can have a negative impact on environmental conditions. The breakdown of deceased individuals causes an increase in the water's pH.
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Physical Characteristics
Pea clams are cream colored with a shiny or dull periostracum. They are 1 mm at birth, growing up to 6 mm. The shell is rounded and inflated, with fine concentric elevated lines. The Umbones are closer to the posterior end of shell.
Habitat
Pea clams are found burrowed in the sediment of creeks, rivers, ponds, springs, marshes, and lakes. In Colorado they overwinter in alpine ecosystems as well as warmer areas of the state.
Diet
Pisids are a bivalve genus with unusual feeding habits; they do not live in the water column, but burrow down into sediment and obtain food (mostly bacteria) from sluggish, watery substrate. They have specialized cilia on their gills as well as on the muscular foot that draws water into the shell. When food has been extracted, water and waste are ejected forcefully through the anal siphon. There is no distinctive incurrent siphon.