Quadrula quadrula


maple leaf
Jim Rathert

Unionidae (freshwater mussels) in the phylum Mollusca


Thick, squared to rounded shell and slightly inflated with two rows of pustules (bumps) radiating from the umbo to the shell margin and separated by a sulcus (smooth depression); anterior portion is usually smooth. Small, slightly raised umbo above hinge line. Epidermis is yellowish-green with faint rays in juveniles; darkens with age to medium to dark greenish-brown or brown. Inside shell beak cavity deep; pseudocardinal teeth serrate and well developed; lateral teeth long and straight; nacre (lining) white, iridescent posteriorly.

Similar species: Wartyback and pimpleback do not have a depression and are more rounded. Purple wartyback is generally more compressed and has purple nacre. Monkeyface has a row of knobs instead of a depression.


Adult length: 3-5 inches.

Habitat and conservation

Quiet sections of medium to large rivers and reservoirs in sand, mud and fine (small to medium) gravel. Favors larger rivers or streams with the characteristics of a big river. Can be found in rivers with clear or turbid water.


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 Mapleleaf Distribution Map
Distribution in Missouri

Widespread, except for the south-central Ozarks.



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--this species uses catfishes. 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 is valuable in the cultured-pearl industry and was used historically for making buttons.

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.