Scientific Name
Lampsilis siliquoidea
Unionidae (freshwater mussels) in the phylum Mollusca

Shell is moderately thick, elongate, anterior end rounded with a blunt posterior end (males) or inflated and squared-off posterior end (females). Umbo is slightly raised above hinge line. Epidermis is smooth, shiny yellow to brownish-yellow, becomes dark chestnut in some older adults; usually distinct green rays. Inside shell beak cavity is moderately deep; pseudocardinal teeth thin to triangular and roughened; lateral teeth blade-like, moderately long and straight; nacre (lining) bluish-white, iridescent posteriorly.

Similar species: Plain pocketbook is more inflated and has a higher umbo. The mucket’s shell is more oval and compressed.


Adult length: 3-6 inches.

Where To Find
image of Fatmucket Distribution Map

Nearly statewide except for north-central and northwest Missouri.

Small to large streams with quiet waters in a wide variety of substrates, including sand and mud. Sometimes found in the soft mud of lakes.

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.

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 host fish for this species include largemouth bass, common shiner, white sucker, white bass, rock bass, bluegill and more. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.

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 fatmucket was a favorite species harvested for the button industry in the early 1900s.

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.

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Similar Species
About Aquatic Invertebrates in Missouri
Missouri's streams, lakes, and other aquatic habitats hold thousands of kinds of invertebrates — worms, freshwater mussels, snails, crayfish, insects, and other animals without backbones. These creatures are vital links in the aquatic food chain, and their presence and numbers tell us a lot about water quality.