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Montana Field Guide

Montana Field Guides

Arctic Fingernailclam - Sphaerium nitidum

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 small, less than 8 mm long; posterior end and dorsal margin rounded or forming an obtuse angle; striae maintain their spacing and height in the region of the beaks (La Rocque 1967).

Range Comments
Northern Canada south to the northern United States and in the Rocky Mountains south to Utah (Burch 1972).

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

(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)

An arctic and alpine species that occurs in small and large lakes and in rivers of various widths, on diverse substrates (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.

It is a favorite food of arctic fish (Clarke 1981).

Reproductive Characteristics
Up to 6 young, mostly of varying sizes, have been found in adult specimens (Clarke 1981).

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