The Arkansas brokenray only occurs in streams that flow south off of the Salem and Springfield plateaus, so it is found only in about the southern quarter of Missouri.
Externally, the Arkansas brokenray's shell is relatively thin, elliptical to oval, and moderately inflated. The posterior ridge is indistinct and broadly rounded. The umbo (beak) is low, only slightly raised above the hinge line. The beak sculpture consists of inverted, V-shaped ridges. The periostracum (thin outer layer) is smooth, shiny, and yellowish brown; green rays are numerous posteriorly.
Inside the shell, the beak cavity is shallow; the pseudocardinal teeth are small, erect, roughened, and often divergent; the lateral teeth are short, straight to slightly curved, and bladelike; the nacre (mother-of-pearl layer) is iridescent white to bluish white to 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 ellipse is more elongate and thicker with well-developed, stout teeth. The fatmucket and northern brokenray (Lampsilis brittsi) are also similar.
Adult length: 2–4 inches.
Occurs only in streams that flow south off of the Salem and Springfield plateaus, so it is found only in about the southern quarter of Missouri.
Habitat and Conservation
Cool, clear headwaters to moderate-sized rivers with noticeable 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 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.
The Arkansas brokenray has been recorded using several different types of host fish, including the banded sculpin, smallmouth and rock bass, bluegill, white crappie, and certain types of sunfishes, darters, minnows, suckers, and more. After it develops sufficiently, 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.
