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Montana Field Guide

Montana Field Guides

Adam Peaclam - Pisidium adamsi

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 introduced Asian clams of the family Corbiculidae, which have not been reported in Montana, yet.

Diagnostic Characteristics
Shell long in outline, height less than 90 percent of length; surface dull; striae fine (15 or more per mm); cusps of P I distal; cusp of P II on distal side of center. L. 6.0, H. 5.0, D. 4.0 mm (La Rocque 1967).

Range Comments
La Rocque (1967) includes Montana in range, indicates the species occurs throughout the Mississippi River drainage. Burch (1972) records the species for nearly all of the United States east of the Rocky Mountains except for the south central states and in Canada from Nova Scotia west to Saskatchewan.

Although the species has a wide range of adaptability, it apparently prefers quiet water in rivers, lakes, and ponds, often among muck and decaying vegetable matter. Observations indicate it is found in quiet water at a depth of 0.3 to 15.5 m, with a pH of 6.05-7.7, and fixed carbon dioxide levels of 2.75-18.36 ppm. Although it seems to prefer muddy bottoms it has also been found in mud and marly-clay bottoms and among pebbles (La Rocque 1967). Clarke (1981) indicates it lives in ponds, lakes, rivers, and streams of at least 8 m in width, and is usually found in mud.

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
Litter sizes of from 10 to 66 young have been recorded (Clarke 1981).

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