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Montana Field Guide

Montana Field Guides

Herrington Fingernailclam - Sphaerium occidentale

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 fade out in the region of the beaks; beaks prominent, distinctly raised above the dorsal margin; anterior and posterior ends of the shell rounded, beaks not swollen (La Rocque 1967).

Range Comments
The species is found in regions containing calcareous deposits and has an uneven distribution from British Columbia south to Georgia, Utah, and Colorado (Clarke 1981).

Observations in Montana Natural Heritage Program Database
Number of Observations: 24

(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)

Prefers water bodies that dry up for a part of each year. Typical sites are ditches, swamps, and small shallow ponds, but also occurs among damp leaves. More amphibious than other North American bivalve molluscs (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
Adults contain only a few young, about 2 to 5, which are all of the same size (Clarke 1981).

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