Ellipse and Bleedingtooth

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

Both species are very similar in appearance. Shell is small, relatively thick, elliptical to elongate, compressed to moderately inflated with a bluntly pointed (ellipse shown) to acutely rounded (bleedingtooth) posterior end and a thicker anterior end (ellipse). Umbo is low and slightly raised above hinge line. Epidermis is yellowish-brown to brown in adults with many fine dark green rays. Inside shell beak cavity is shallow; pseudocardinal teeth triangular, heavy and roughened; lateral teeth short, thick and straight to slightly curved; teeth sometimes rusty-red; nacre (lining) bluish-white and often tinged with rusty salmon.

Similar species: Juvenile muckets are shorter, stouter and uniformly thick and lack the fine rays. Brokenray is shorter, more rounded and thinner and females often have an indentation in the posterior margin.

Size: 
Adult length: 1-3 inches.
Habitat and conservation: 
Small to relatively large rivers in noticeable current with firm sand or mixed sand and gravel.
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: 
Mostly south of the Missouri River: Northward-flowing (ellipse) and southward- and westward-flowing (bleedingtooth) streams arising from the Springfield and Salem plateaus.
Status: 
Fairly common, although degrading water quality and watershed destabilization interfere with the survival of these and all freshwater mussels. The bleedingtooth (V. pleasii) has also been called Plea's mussel.
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 (darters are the host fish for this species). 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.