Missouri may have the largest number of spectaclecase mussels left in the world. This species is endangered in Missouri and federally. It occurs mostly in the Meramec and Gasconade rivers.
Externally, the spectaclecase's shell is elongated and compressed, with rounded ends; it is somewhat pinched in the middle. The umbo (beak) is slightly elevated above the hinge line. The periostracum (thin outer layer) is flaky and dark brown to black.
Inside the shell, the beak cavity is shallow. The pseudocardinal teeth are pronglike, and the lateral teeth are poorly developed. The nacre (mother-of-pearl layer) is 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: The black sandshell (Ligumia recta) has a sharply pointed posterior and lacks a flaky epidermis. The adult spike (or ladyfinger) is neither as elongated nor as pinched in shape.
Adult length: 5–8 inches.
Tributaries of the Missouri and Mississippi rivers, also the Salt River. Concentrated mostly in the Meramec and Gasconade rivers.
Habitat and Conservation
Medium to large rivers, in reduced current adjacent to swift water, among boulders, or in patches of gravel, sand, and cobble. Spectaclecases live in large groups with up to 100 per square yard.
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 Missouri and federally.
This species is vulnerable, as the population is concentrated mostly in the Meramec and Gasconade rivers. It can be locally abundant. Potential threats to the survival of this species include water quality degradation and watershed destabilization.
The spectaclecase is Missouri's only freshwater mussel in family Margaritiferidae. The others are in family Unionidae.
This species is the only surviving member of its genus. Other members of the formerly widespread genus Cumberlandia appear in the fossil record as far back as 125 million years ago.
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, the host species are the world's two living species in the mooneye family, the mooneye and the goldeye, though it has been recorded on bigeye chub, too. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats. These elongated shellfish can live for 60 years or more.
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. Some 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.
