The white heelsplitter's shell is impressively large. Although fairly flat, it can be more than 8 inches long. A large wing on the heelsplitter can be painful if you step on it. In Missouri, it is widespread, except for the south-central Ozarks.
Externally, the white heelsplitter's shell is large, very compressed, and rounded, with a large wing above the hinge line. The umbo (beak) is flattened, small, and not raised above the hinge line. The periostracum (thin outer layer) is green or greenish brown, often with faint rays, becoming dark brown to black with age.
Inside the shell, the beak cavity is shallow; the pseudocardinal teeth are large; the lateral teeth are bladelike and poorly developed; the nacre (mother-of-pearl layer) is bluish white to 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 pink heelsplitter is more inflated, with a pinkish-purple nacre. The pink papershell is generally smaller with a thinner shell and purple nacre. The fragile papershell is also similar.
Adult length: 4–8 inches.
Widespread, except for the south-central Ozarks. Prefers the muddy, turbid streams of central Missouri and the tributaries of the Mississippi in eastern Missouri.
Habitat and Conservation
Typically found in rivers having characteristics associated with larger rivers: streams that are usually sluggish and turbid with mud or mud-gravel, sand, or fine gravel bottoms; also in lakes and ponds. Rarely, if ever, found in the upper reaches of rivers flowing off the plateaus.
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, although degrading water quality and watershed destabilization interfere with the survival of this and all freshwater mussels.
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, common carp, green sunfish and a few other sunfishes, largemouth bass, white crappie, and a few other species. 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.
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.
