Missouri's Freshwater Mussels

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Published on: Aug. 2, 1999

Last revision: Nov. 3, 2010

are hard to identify. Nevertheless, with a little practice you can learn to identify the more common species near your own home.

Shells of freshly dead mussels, picked clean and discarded in a pile by a muskrat or raccoon, are the best to start with. Some features to inspect include shape and thickness of shell, color of the shell exterior and interior, presence of bumps, pustules or ridges on the shell exterior and shape and size of internal teeth.

A good reference book is Missouri Naiades: A Guide to the Mussels of Missouri by Ronald D. Oesch (Copyright 1984, 1995). This manual contains excellent line drawings and detailed descriptions of each species. It is available from Nature Shop, Missouri Department of Conservation, P.O. Box 180, Jefferson City, Missouri 65102-0180 for $6. Shipping and handling is $2. Missouri residents must include 6.225 percent sales tax.

Feeding and reproduction

The bulk of a freshwater mussel consists of a long muscular foot that contracts and withdraws into its shell if pulled from the substrate. On either side of the foot is a pair of thin, specialized gills that allow the mussel to breathe and filter-feed.

Water is drawn into the body or mantle cavity through the incurrent siphon and passes over the gills, which extract critical oxygen and food (algae and fine particles of decaying organic matter). While food travels to the mussel's stomach, sediment and undigested wastes travel and exit the body through its excurrent siphon. Upon exiting, these "pseudofeces" are in a form other aquatic animals can eat.

Freshwater mussels have a complex life cycle in which the larval stage is parasitic on a host, typically a fish. During the breeding season, males release sperm into the water, which enter the female via her incurrent siphon and fertilize her eggs. Her modified gills serve as a brooding chamber for developing embryos that mature into larvae called glochidia (glo-kid-ee-ah).

Glochidia, which have specialized teeth or hooks on the inside of their microscopic shells, are often contained in a gelatinous packet called a conglutinate, which takes on a shape and size unique to each mussel species. Various mussel species have unique tactics for attracting particular host fishes that share their same habitat. The mantle flap of female pocketbooks, for example, mimics a young fish. She contracts this "lure" to draw the attention of a nearby bass, its host. When the bass attempts to eat the "fish," it gets a mouthful

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