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Swamp Fingernailclam - Musculium partumeium
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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
"Large shells, more than 8 mm long, may be distinguished by their prominent beaks, distinctly raised above the dorsal margin; the higher outline of the shell as compared with S. TRANSVERSUM, the height in S. PARTUMEIUM being 7/8 or more of the length; the rather straight dorsal margin, the posterior end more or less at right angles to the dorsal margin; and the very fine striae. Small shells, less that 8 mm long, in contrast with S. SECURIS, have the anterior ventral margin of the shell sloping upward, but only slightly, a glossy surface, and finer striae." La Rocque (1967:300). La Rocque (1967:300) cites dimensions from various authors in the following ranges: L. 13.5-2.6, H. 11.5-2.2, D. 9-1.4 mm.
Range Comments
La Rocque (1967:301) includes Montana in range, indicates the species occurs throughout the Mississippi and Missouri River drainages. Burch (1972:6) indicates the species is found throughout the United States; and in southern Canada from New Brunswick to Saskatchewan. Elrod (1902b:103) indicates the species was collected at Swan Lake and in ponds near Flathead Lake, and at Daphnia Pond (1902:170). Henderson (1924:92) cites same data. Sterki (1916:44) records collections in Montana east of the Rocky Mountains.
Habitat
The species is found in ponds, small lakes, swamps, and slow-moving streams. It prefers muddy bottoms and is fairly common. It has been collected in various areas including: ponds and eddies in rivers with considerable vegetation and soft bottoms; a creek and a small river; streams; the outlet of a lake; trenches; a brook; summer-dry pools and temporary ponds; ponds in black mud in shallow water (La Rocque 1967:300). Clarke (1981:380) indicates the species is common and occurs in small and large lakes, swamps, ponds, vernal ponds and slow moving streams of all sizes. Usually found in mud.
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 (2-30), all in a few discrete size classes are held within each parent." (Clarke 1981:380).
References
Literature Cited AboveLegend: Mollusca:Pelecypoda ) of North America. EPA Biota of Freshwater Ecosystems Identification Manual No. 3. 31 pp.
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