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Montana Field Guide

Montana Field Guides

Pond Fingernailclam - Musculium securis

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 nearly at right angles with dorsal margin; anterior ventral margin of shell slopes sharply upward; surface dull; striae coarser than in S. partumeium. Dimensions from several authors in the following ranges: L. 6.3-5.5, H. 5.2-4.4, D. 3.2-3.0 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 most states in the United States, except the southwestern states; and in Canada from Nova Scotia to British Columbia.

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 ponds, lakes, and rivers; frequently in fine sand. Collections have been made in the following habitats: a swale in water a few inches deep with a muddy bottom; a lake in water plants, 3-5 m deep; an old stone quarry; trenches; a small lake; a creek; in a small permanent or nearly permanent pond in sandy bottom among dense vegetation in shallow water (La Rocque 1967). Clarke (1981) indicates the species occurs in ponds, lakes, rivers and streams of all sizes, and in both vernal and perennial-water habitats. It is usually found in mud among abundant vegetation.

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 young in up to three size classes are found in most adult specimens (Clarke 1981).

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