Scientific Name
Truncilla truncata
Unionidae (freshwater mussels) in the phylum Mollusca

Shell is solid, thick, inflated, mostly triangular; prominent posterior ridge drawn to a rounded point at the posterior end. Umbo is wide and raised above hinge line. Epidermis is yellowish-brown to brown; numerous green rays vary in width with spots, zigzags or most often V-shapes (chevrons); sometimes without rays. Inside shell beak cavity is moderately deep; pseudocardinal teeth are triangular, grooved and well developed; lateral teeth are short, thin, grooved and straight to slightly curved; nacre (lining) white, rarely pinkish-salmon.

Similar species: Butterfly has a flattened appearance and less developed rays. Fawnsfoot is easily confused with the deertoe, but is longer with a less prominent dorsal ridge and more distinct zigzag marks covering the shell.


Adult length: up to 3 inches.

Where To Find
image of Deertoe Distribution Map

Sporadic, may be locally common where found. Southeastern Missouri, Salt River in eastern Missouri, and in an east-west band in north-flowing rivers draining the Salem and Springfield plateaus.

Medium to large rivers with moderate to swift current in a variety of substrates from mud-gravel to larger rocks and in water depths from several inches to a few feet.

Algae and fine particles of decaying organic matter; extracts nutrients and oxygen from water drawn into the body cavity through a specialized gill called the incurrent siphon; sediment and undigested waste are expelled through the excurrent siphon.

Locally common where found.

Life Cycle

Males release sperm directly into water. Females downstream siphon sperm into the gill chamber, where eggs are fertilized. Eggs mature into larvae (called glochidia), which discharge into the water and attach to host fish--for this species, the sauger and freshwater drum. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.

Mussels are excellent biological indicators of water quality because they are long-lived and relatively immobile, accumulating contaminants in water that can be scientifically analyzed.

Mussels act as nature's “vacuum cleaners,” filtering and cleansing polluted waters. They are also an important food source for other species in the aquatic environment.

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Similar Species
About Aquatic Invertebrates in Missouri
Missouri's streams, lakes, and other aquatic habitats hold thousands of kinds of invertebrates — worms, freshwater mussels, snails, crayfish, insects, and other animals without backbones. These creatures are vital links in the aquatic food chain, and their presence and numbers tell us a lot about water quality.