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Montana Field Guide

Montana Field Guides

Long Fingernailclam - Musculium transversum

Native Species

Global Rank: G5
State Rank: SNR

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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 large, more than 8 mm long; beaks prominent, distinctly raised above the dorsal margin; shell long in outline, height 3/4 or less of length. Dimensions from various authors and collection sites in the following ranges: L. 14.3-3.9, H. 10.5-3.0, D. 6.9-1.8 mm (La Rocque 1967).

Range Comments
La Rocque (1967) includes Montana in range, indicates the species occurs throughout the Mississippi drainage and is present in the Missouri River drainage. Burch (1972) records the species for "the United States east of the Rocky Mountains, south to Florida, Texas and Mexico" and in Canada the southwestern Northwest Territories and provinces east of the Rocky Mountains. Clarke (1981) indicates the species occurs throughout North America but is not present in most far western states in the United States.

The species is found in large lakes, rivers, and sloughs. It has been recorded in rivers with strong current, with stony and rocky bottom and quiet water or slow currents in sand and mud (La Rocque 1967).

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
A few up to many young (5-34) in up to four size classes have been observed in individual adult Canadian specimens (Clarke 1981).

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Citation for data on this website:
Long Fingernailclam — Musculium transversum.  Montana Field Guide.  .  Retrieved on , from