Scaleshell

Family: 
Unionidae (freshwater mussels) in the phylum Mollusca
Description: 

Shell relatively small, elongate, thin, and compressed. Anterior end rounded, posterior end pointed. Dorsal margin straight, ventral margin straight to broadly curved. Umbos small and low, about even with the hinge line. Beak sculpture, if visible, of 4 or 5 double-looped ridges. Shell smooth, yellowish-green or brown, with numerous faint green rays.

Pseudocardinal teeth reduced to a small thickened ridge. Lateral teeth moderately long; 2 low, indistinct lateral teeth in left valve, 1 fine tooth in the right. Beak cavity very shallow or absent. Nacre pinkish white or light purple and highly iridescent.

Similar species: Fragile papershell

Size: 
Adult length: up to 4 inches.
Habitat and conservation: 
Occurs in clear, nonpolluted riffles with moderate current and firm gravel, cobble or sand substrates.
Foods: 
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.
Distribution in Missouri: 
Found only in the Gasconade and Meramec river basins.
Status: 
Listed as Endangered by both the Missouri Department of Conservation and the U.S. Fish and Wildlife Service. Current threats include loss of habitat, competition from exotic zebra mussels and overharvesting and illegal collection.
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. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
Human connections: 
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.
Ecosystem connections: 
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.