The elephantear occurs in central, eastern, and southeastern Missouri, in the Big Piney, Black, Castor, Gasconade, Meramec, Mississippi, Osage, Pomme de Terre, and Sac rivers. It is listed as endangered within the state of Missouri and is vulnerable to extirpation from our borders.
Externally, the elephantear's shell is thick, solid, compressed to moderately inflated, and triangular. The anterior end is rounded; the posterior end is pointed. The dorsal margin is slightly curved; the ventral margin is curved in young shells, becoming straight in older shells. The umbo (beak) is low, usually not elevated above the hinge line. The beak sculpture, if visible, is of two or three loops parallel to the growth lines (usually present only in very small shells). The posterior ridge is prominent and sharply angled. The surface of the shell is smooth. The periostracum (thin outer layer) is reddish brown with faint green rays in small shells, becoming dark brown to black in adults.
Inside the shell, the beak cavity is very shallow. The pseudocardinal teeth are well developed, with two in the left valve (shell) and one in the right. The lateral teeth are short, roughened, and straight. The nacre (mother-of-pearl layer) color is variable, usually purple, occasionally pink or white.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Adult length: 3–6 inches.
Occurs in central, eastern, and southeastern Missouri, in the Big Piney, Black, Castor, Gasconade, Meramec, Mississippi, Osage, Pomme de Terre, and Sac rivers.
Habitat and Conservation
Large rivers in mud, sand, or fine gravel.
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
A Missouri species of conservation concern, listed as endangered in our state.
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 Missouri, this species uses the skipjack herring. 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. Because of its purple nacre, the elephantear was not sought after by the commercial button industry.
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.
