In spikes, the nacre (shell lining) color varies from purple to pink to white. In smaller rivers, the shell is much thinner than in larger rivers. In Missouri it is most common in rivers south of the Missouri River. In the northern part of the state, its range has been severely reduced by siltation and channelization.
Externally, the spike's shell is thick, slightly inflated to compressed, and elongate; it is generally twice as long as tall; the ventral margin is nearly straight. The umbo (beak) is low and rarely raised above the hinge line. The periostracum (thin outer layer) is greenish brown with faint green rays, becoming dark brown to black with age.
Inside the shell, the beak cavity is shallow to absent; the pseudocardinal teeth are triangular and streaked; the lateral teeth are short and straight; the nacre (mother-of-pearl layer) is purple, white, or salmon.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Similar species: Young or small spectaclecases could be confused with the spike, but they appear pinched. The black sandshell (Ligumia recta) is longer and thicker with a more prominent posterior ridge and a shiny exterior that is usually darker. Also similar are the elephantear and the Ouchita kidneyshell (Ptychobranchus occidentalis).
Adult length: 3–5 inches.
Common and locally abundant south of the Missouri River; also present in northeast Missouri.
Habitat and Conservation
Small to large streams with moderate to strong current in stable sand and 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
Common in rivers south of the Missouri River. In the northern part of the state, its range (like that of many mussels) has been severely reduced by siltation and channelization, although it persists in at least two northern rivers on the eastern side of 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 has been recorded using gizzard shad, flathead catfish, white and black crappies, largemouth and rock basses, yellow perch, some types of darters, and several other kinds of fishes. 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. Some species are still commercially important in the cultured pearl and jewelry industries. Like most mussels with thick shells, this species holds value for the polished chip 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.
