A common mussel in some areas, the deertoe has decorative green markings. It is found mostly in the eastern half of the state.
Externally, the deertoe's shell is solid, thick, inflated, and mostly triangular; the prominent posterior ridge is drawn to a rounded point at the posterior end. The umbo (beak) is wide and raised above the hinge line. The periostracum (thin outer layer) is yellowish brown to brown; the numerous green rays vary in width, with spots, zigzags, or most often V-shapes (chevrons); some individuals lack rays.
Inside the shell, the beak cavity is moderately deep; the pseudocardinal teeth are triangular, grooved, and well developed; the lateral teeth are short, thin, grooved, and straight to slightly curved; the nacre (mother-of-pearl layer) is white, rarely pinkish 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: The butterfly has a flattened appearance and less developed rays. The fawnsfoot (Truncilla donaciformis) is easily confused with the deertoe, but is longer with a less prominent dorsal ridge and more distinct zigzag marks covering the shell. The Wabash pigtoe and snuffbox are also similar.
Adult length: up to 3 inches.
Occurs in southeastern Missouri, the Salt River in eastern Missouri, and in an east-west band in north-flowing rivers draining the Salem and Springfield plateaus.
Habitat and Conservation
Medium to large rivers with moderate to swift current in a variety of substrates from mud-gravel to larger rocks and in water depths from several inches to a few feet. Sporadic; may be locally common where found.
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
Locally common where found.
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 — for this species, the freshwater drum and the sauger. 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.
