The butterfly is one of the most beautiful of Missouri’s mussels. It is most common in an east-west band of north-flowing tributaries of the Missouri River and in several Mississippi River tributaries.
Externally, the butterfly's shell is solid, thick, noticeably laterally flattened, and triangular, with a prominent and sharply angled posterior ridge. The umbo (beak) is flattened on the sides, directed forward, and slightly raised above the hinge line. The periostracum (thin outer layer) is yellowish brown with interrupted but distinct brown rays that appear as spots, bars, wavy patterns, or V-shapes (chevrons).
Inside the shell, the beak cavity is shallow; the pseudocardinal teeth are large, grooved, and triangular; the lateral teeth are serrate, short, and straight; the nacre (mother-of-pearl layer) is white.
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 deertoe has a similar color pattern, but the shell is much more inflated and has a deeper beak cavity. The mucket is also similar.
Adult length: 3–5 inches.
Most common in an east-west band of north-flowing tributaries of the Missouri River and in several Mississippi River tributaries.
Habitat and Conservation
Large rivers with strong current in coarse gravel and sand.
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 but restricted.
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 butterfly, the principal fish host is the freshwater drum. 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, and this was one of them. 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.
