Pistolgrip (Buckhorn)

Tritogonia verrucosa


Jim Rathert

Unionidae (freshwater mussels) in the phylum Mollusca


Shell is heavy, compressed and elongate; covered with pustules (knobs); pronounced, knobby posterior ridge with flutings and folds extending to margin. Umbo is slightly elevated above hinge line, turned forward. Epidermis is light green to brown in juveniles and brown or black in adults. Inner shell beak cavity moderately deep; pseudocardinal teeth large and serrate; lateral teeth long, straight and heavy; nacre (lining) usually white, iridescent posteriorly.


Adult length: 4-7 inches.

Habitat and conservation

Medium to large rivers with moderate current in stable gravel and sand or mud. Has been found on almost any kind of substrate.


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

image of Pistolgrip Buckhorn Distribution Map
Distribution in Missouri

Widespread, sometimes locally common.


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. 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. This species was used in the button industry and also in the Japanese cultured pearl industry.

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.