The purple wartyback has a thick, heavy, nearly round shell covered with many bumps. It is moderately common and occurs mainly in the Ozarks.
Externally, the shell of the purple wartyback is thick, heavy, nearly round, compressed (in shells from small rivers) to inflated (from large rivers), and covered with many bumps; the anterior end is rounded, the posterior end is squared off. The umbo (beak) is slightly raised above the hinge line. The periostracum (thin outer layer) is yellowish brown to greenish brown, becoming darker with age; greenish rays may be present in juveniles.
Inside the shell, the beak cavity is deep and wide; the pseudocardinal teeth are massive, widely spaced, and deeply grooved; the lateral teeth are short and straight or slightly curved; the nacre (mother-of-pearl layer) is deep coppery purple.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Similar species: The pimpleback and wartyback are less massive and less compressed and have white nacre and smaller pseudocardinal teeth. The mapleleaf has a definite sulcus, white nacre, and smaller pseudocardinal teeth.
Adult length: 2–4 inches.
Mainly in the Ozarks, in almost all the rivers arising on the Salem and Springfield plateaus. Rare elsewhere, though it is also found in the Salt and Fabius rivers.
Habitat and Conservation
Occurs in medium to large rivers with moderate current in sand, gravel, and cobble.
Food
Freshwater mussels consume algae, bacteria, and fine particles of decaying organic matter. They extract nutrients and oxygen from water drawn into the body cavity through a specialized structure called the incurrent siphon; sediment, undigested food, and waste (called pseudofeces) are expelled through the excurrent siphon.
Status
Moderately common in specific regions, 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 the case of the purple wartyback, recorded host fish are catfish: flathead and channel catfish and black and yellow bullheads. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
Human Connections
Mussels play important roles in maintaining the health of Missouri’s water resources:
- As food for fish, they are important for Missouri’s fisheries. Small mammals and some birds eat them, as well.
- They filter algae, bacteria, and other particles from the water, improving water quality and cycling nutrients and energy in streams and lakes. Clean water is necessary for people and nature.
- Because mussels are sensitive to habitat disturbance and pollution, they are good indicators of the overall health of aquatic ecosystems and water quality.
The shells of several types of mussels were an important resource historically for button manufacture. Before buttons were made of plastic, they were made of shell. Because only white buttons were in demand, the coppery-purple shell of this species made it worthless for the commercial button industry.
Some mussel species are still commercially important in the cultured pearl and jewelry industries.
Ecosystem Connections
Native freshwater mussels provide vital functions in aquatic ecosystems:
- They are an important food source for many species of fish, wildlife, and other invertebrates.
- Their shells, both while the animal is alive and after it dies, provide habitat for other organisms.
- As filter feeders, individual mussels can filter a significant amount of water per day, but not all of what they remove is eaten. What they don’t eat is combined with mucus into packets. These pseudofeces packets are eaten by some fish and invertebrates.
Freshwater mussels depend on healthy populations of certain types of fish to complete their life cycle. Although as larvae they temporarily parasitize these fish, the harm to the fish is negligible.
