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.

Shell up to about 15 mm long, moderately high (H/L 0.72-0.82), compressed to inflated (W/L 0.47-0.62), more or less ovate, and with shell walls of medium thickness. Beaks low, and slightly anterior. Dorsal margin curved and rather long, ventral margin more openly curved and longer, and anterior and posterior margins obliquely flattened above and rounded below. Hinge plate long and somewhat unevenly curved; lateral teeth short, strong, and at the ends of the hinge plate. Concentric striae very fine on the beak and a little coarser on the body of the shell. Periostracum shiny, yellowish to brownish, and with dark-brown or greenish concentric bands in many specimens. Similar to the eastern S. fabale, but is larger and more dull in appearance (Clarke 1981).

The species occurs in lakes, rivers, sloughs, and streams. Details of substrate preference have not been recorded (Clarke 1981).

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.