Epioblasma triquetra


Jim Rathert
Species of Conservation Concern

Unionidae (freshwater mussels) in the phylum Mollusca


Shell small, fairly solid, triangular (males) to somewhat elongate (females) and inflated (particularly in females). Anterior end rounded, posterior end truncated in males, expanded in females. Dorsal and ventral margins straight to slightly curved. Posterior ridge sharply angled, posterior slope wide, expanded and ribbed (especially in females). Umbos swollen and slightly elevated above the hinge line. Beak sculpture of three or four faint, double-looped bars. Periostracum yellow or yellowish-green, with numerous dark green rays, blotches or chevron-shaped markings.

Pseudocardinal teeth elevated, roughened, relatively thin and compressed; two in the left valve, two in the right, with the front one being thinner and much smaller. Lateral teeth very short, slightly curved, serrated and elevated. Beak cavity fairly deep. Nacre pearly white, iridescent posteriorly.

Similar Species: Elktoe, deertoe, and fawnfoot


Adult length: up to 2 1/2 inches

Habitat and conservation

Medium to large rivers in clear water with gravel riffles, usually buried in the gravel.


Algae and fine particles of decaying organic matter; extracts nutrients and oxygen from water drawn into body cavity through a specialized gill called the incurrent siphon; sediment and undigested waste are expelled through the excurrent siphon.

image of Snuffbox Distribution Map
Distribution in Missouri

A very limited range in southeastern Missouri and the Ozarks, primarily the Bourbeuse, Meramec and St. Francis rivers.


Endangered in Missouri; candidate for federal Endangered status.

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 tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.

Human connections

Mussels are excellent biological indicators of water quality because they are long-lived and relatively immobile, accumulating contaminants in water that can be scientifically analyzed. The snuffbox is a small shell of unusual shape and beauty.

Ecosystem connections

Mussels act as nature's “vacuum cleaners,” filtering and cleansing polluted waters. They are also an important food source for other species in the aquatic environment.