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Montana Field Guide

Montana Field Guides

River Fingernailclam - Sphaerium fabale

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
Surface uneven; shell compressed; striae not evenly spaced and weaker in the region of the beaks. Dimensions in the range: L. 11.25-4.6, H. 9.0-3.8, D. 5.9-1.6 mm. (La Rocque 1967).

Range Comments
The species is found from southern Ontario to Georgia and Alabama, and as far west as Michigan Clarke 1981). (Sterki 1916) indicates the species was collected in the Bitterroot Mountains.

Observations in Montana Natural Heritage Program Database
Number of Observations: 1

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

The species is found in rivers and streams and does not occur in lakes. It is found in gravel and in gravelly sand in cracks in a limestone bottom (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.

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Citation for data on this website:
River Fingernailclam — Sphaerium fabale.  Montana Field Guide.  .  Retrieved on , from