Spike (Ladyfinger)

Scientific Name
Elliptio dilatata
Unionidae (freshwater mussels) in the phylum Mollusca

Shell is thick, slightly inflated to compressed and elongate; generally twice as long as wide; ventral margin either straight or slightly curved in juveniles. Umbo is low and rarely raised above hinge line. Epidermis is greenish-brown with faint green rays, dark brown to black with age. Inside shell beak cavity shallow to absent; pseudocardinal teeth triangular and streaked; lateral teeth short and straight; nacre (lining) purple, occasionally pink or white.

Similar species: Young or small spectaclecase could be confused with the spike, but they appear pinched. The black sandshell is longer and thicker with a more prominent posterior ridge and a shiny exterior that is usually darker.


Adult length: 3-5 inches.

Where To Find

Common and locally abundant south of the Missouri River; also in northeast Missouri.

Small to large streams with moderate to strong current in stable sand and gravel.

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.

Common in rivers south of the Missouri River. In the northern part of the state, its range (like that of many mussels) has been severely reduced by siltation and channelization, although it persists in at least two northern rivers on the eastern side of the state.

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—in this species, gizzard shad, flathead catfish, white and black crappies and yellow perch. 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. Like most mussels with thick shells, this species holds value for the polished chip industry.

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.