Wabash Pigtoe
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Family:
Unionidae (freshwater mussels) in the phylum Mollusca
Description:
Shell is variable, usually thick, square to triangular, somewhat compressed (creeks and small rivers) to inflated (large rivers); a broad sulcus (smooth depression) extends from umbo to ventral margin. Umbo moderately to highly elevated above hinge line. Epidermis yellowish-brown with faint green rays in juveniles, becomes dark brown with age. Inside shell beak cavity deep; pseudocardinal teeth rough and well-developed; lateral teeth serrate and straight to slightly curved; nacre (lining) white, often tinged with salmon.
Similar species: Wabash pigtoes are easily confused with round pigtoes, which generally lack a sulcus and have a rounded appearance.
Size:
Adult length: 2-4 inches.
Habitat and conservation:
Medium to large rivers in moderate current with a stable mix of coarse 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:
Widespread; most common in north-flowing streams south of the Missouri River; also Salt River.
Status:
Common, although degrading water quality and watershed destabilization interfere with the survival of this and all freshwater mussels.
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, white crappie, black crappie and bluegill. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
Human connections:
Mussels are excellent indicators of water quality because they are long-lived and relatively immobile, accumulating contaminants in water that can be analyzed. Large individuals of this species were used in the button industry and have value in the pearl and polished chip industries.
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.