Montana Field Guide

Fingernail clams are small "mostly about the size of a finger or thumbnail" bottom-dwelling, filter-feeders found in ponds, lakes and streams throughout Montana. They are native and can be quite abundant, providing food for a variety of animals and producing large accumulations of empty shells. These shells can be quite fragile compared to introduced Asian clams of the family Corbiculidae, which have not been reported in Montana, yet.

Anterior cusp of left valve not twisted, but parallel to the dorsal margin; shell tapering ventrally in end view; hinge long (more than 3/4 shell length); anterior end rounded; shell without heavy ridges or ridges, if present, only on the beaks; cardinals central or subcentral; shell commonly shaped like a parallelogram, i.e., anterior and posterior ends sloped at the same angle; found only in cold waters. Dimensions in the following range: L. 3.2-1.3, H. 2.8-1.0, D. 2.0-0.5 mm (La Rocque 1967).

The species is not found in warm water. At northern latitudes it can be collected along the shoreline, however farther south it will only be found in deep water or at high altitudes. The habitat of this species is well known in Europe where it is found in alpine lakes in the sublittoral and deep parts, where it lives from 5-8 m to 70 m and more in depth (exceptionally down to 300 m). (La Rocque 1967). Clarke (1981) indicates this cold water species is found at all depths in the arctic and subarctic regions, and at considerable depths in the temperate parts of its range.

Fingernail clams are mostly filter-feeders, siphoning in floating particulate organic materials ( small plant or animal) from the water column and straining out the particles and expel the strained water. Pedal feeding from the bottom with the foot muscle has also been observed.

Two broods of young are produced each year, 1 in summer and 1 in winter (Clarke 1981).