The ebonyshell is a species of conservation concern in Missouri. It has been found in the Mississippi, Meramec, Osage, and Little Black rivers.
Externally, the ebonyshell's shell is solid, heavy, rounded or oval, and inflated. The anterior end is rounded; the posterior end is rounded or bluntly pointed. The dorsal margin is slightly rounded; the ventral margin is curved, occasionally straight. The umbo (beak) is low, inflated, about even with the hinge line, and anteriorly curved. The beak sculpture consists of a few very weak ridges, apparent only in extremely small shells. The shell is smooth with slightly elevated ridges indicating periods of growth. The periostracum (thin outer layer) is rayless, light brown in young shells, becoming dark brown to black in older individuals.
Inside the shell, the beak cavity is very deep. The pseudocardinal teeth are very heavy and well developed, with two in the left valve (shell) and two in the right. The lateral teeth are serrated and curved; two in the left valve, one in the right. The nacre (mother-of-pearl layer) is pearly white, iridescent posteriorly.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Similar species: Pigtoes (Fusconaia and Pleurobema) are quite similar; these include the Wabash pigtoe, round pigtoe, Ohio pigtoe (Pleurobema cordatum), and pyramid pigtoe (Pleurobema rubrum). The hickorynut (Obovaria olivaria) is also similar.
Adult length: up to 4 inches.
Has been found in the Mississippi, Meramec, Osage, and Little Black rivers.
Habitat and Conservation
Usually found in rivers with swift current and a substrate of fine gravel to 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
A Missouri species of conservation concern. Listed as endangered in the state of Missouri; critically imperiled to extirpation from the 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; this species uses skipjack herring and largemouth bass, but it has been recorded using several more types, ranging from minnows to the freshwater drum and channel catfish. 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. The ebonyshell was one of the most valuable to 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.
