The Arkansas brokenray's shell is relatively thin, elliptical to oval (females) with rounded anterior margin; sharply rounded to angular posterior margin (males); more broadly rounded posteriorly with slight indentation on posterior margin (females). Umbo is low, only slightly raised above hinge line. Epidermis is smooth, shiny yellowish-brown; green rays numerous posteriorly. Inside shell beak cavity is shallow; pseudocardinal teeth small, erect, roughened and often divergent; lateral teeth short, straight to slightly curved, blade-like; nacre (lining) iridescent white to bluish-white to salmon.
Similar species: Ellipse is more elongate and thicker with well-developed, stout teeth.
Adult length: 2–4 inches.
Occurs only in streams that flow south off of the Salem and Springfield plateaus, so it is found only in about the southern quarter of Missouri.
Habitat and Conservation
Cool, clear headwaters to moderate-sized rivers with noticeable 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.
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.
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.