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Montana Field Guide

Montana Field Guides

Tiny Peaclam - Pisidium insigne

Native Species

Global Rank: G5
State Rank: SNR

Agency Status


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General Description
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 the introduced Asian clams , which have not be reported in Montana yet.

Diagnostic Characteristics
Anterior cusp of left valve not twisted but parallel to the dorsal margin; shell evenly tapered ventrally, in end view; hinge long (more than 3/4 shell length); anterior end terminating in a blunt point (La Rocque 1967). La Rocque (1967) cites dimensions from various collection sites in the following range: L. 2.2-1.5, H. 1.8-1.1, D. 1.3-0.7 mm.

Range Comments
Burch (1972) records the species in the northern United States from Maine to Washington, and south in the Rocky Mountains to the southern border states.

The species is most often found in slow-moving creeks and spring creeks (Clarke 1981).

Food Habits
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.

Reproductive Characteristics
Almost nothing is known about its biology (Clarke 1981).

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Citation for data on this website:
Tiny Peaclam — Pisidium insigne.  Montana Field Guide.  .  Retrieved on , from