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Arcidens confragosus

What do they look like?

The rock pocketbook mussel is a relatively large mussel. The shell is elliptical in shape, and can be thin or thick. They are dark green, brown, or black. The front edge of the shell is rounded, while the back end is squared. They have two rows of large folds or heavy ridges that can be used to identify this species. The inner shell is white. The rock pocketbook mussel can measure anywhere from approximately 7 centimeters to 18 centimeters in length. (Jennings, 2012; Martinez, et al., 2002; Roe, 2002)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    7 to 18 cm
    2.76 to 7.09 in

Where do they live?

Arcidens confragosus, the rock pocketbook mussel, is found in the Mississippi River and its tributaries, as well as gulf coastal rivers from the Colorado River in Texas east to the Mobile River System in Alabama. It is currently found in the Mississippi River Basin from Minnesota south to Louisiana and from Ohio west to eastern Kansas. In the south, this mussel is found from eastern Texas east to western Alabama along the Gulf of Mexico. (Martinez, et al., 2002; "Aridens confragosus", 2013; Roe, 2002)

What kind of habitat do they need?

The rock pocketbook mussel lives in medium to large rivers. These mussels burrow into the sand or mud at the bottom of the river. They need good water quality with a lot of food particles so that they are able to feed, breath, and reproduce. The rock pocketbook mussel is found at depths of 10 cm to 1 m in slow or fast flowing waters. (Buchanan, 1980; Jennings, 2012; "Aridens confragosus", 2013; Murray and Leonard, 1962; Roe, 2002)

  • Aquatic Biomes
  • rivers and streams
  • Range depth
    .10 to 1 m
    0.33 to 3.28 ft

How do they grow?

The mussel life cycle begins when a male mussel releases sperm into the water, then the sperm enters the body of a nearby female. Fertilized eggs stay in a pouch in the female where they develop into larvae called glochidia. Glochidia are parasites and need to move from their mother to a fish to complete development. When a fish is near, the glochidia are released from the mother and attach to a fish. The glochidia get buried into the skin to complete development. Some of the fish these mussels use include American eel (Anguilla rostrata), gizzard shad (Dorosoma cepedianum), rock bass (Ambloplites rupestris), white crappie (Pomoxis annularis) and freshwater drum (Aplodinotus grunniens). Within a few weeks, the larval glochidia develop into juvenile mussels and drop from the host fish. Juveniles are found at the bottom of the river where they develop into adults. ("Reproductive Cycle in Mussels", 2003; Arey, 1921; Jennings, 2012; Jirka and Neves, 1992; Lefevre and Winterton, 1910; "Aridens confragosus", 2013)

How do they reproduce?

To mate, males release their sperm into the water. The water carries the sperm to nearby females, where the females take the sperm into their bodies through a tube called the incurrent siphon. Males release their sperm in response to changes in temperature. (Jennings, 2012)

When the females take sperm in, eggs are released into chambers in the gills. The sperm are carried to the eggs and the eggs are fertilized. The eggs stay in this special pouch the females have in the gills, and they hatch there too. When a host fish is nearby, the females release the larvae (called glochidia) into the water through a tube called the excurrent siphon. Females can release anywhere from hundreds to hundreds of thousands of glochidia. ("Status and Life History of the Three Assessed Mussels", 2007; Jennings, 2012; "Aridens confragosus", 2013)

  • How often does reproduction occur?
    The rock pocketbook breeds once yearly.
  • Breeding season
    Females brood their young from September through June.
  • Range number of offspring
    Hundreds to Hundreds of thousands

Females provide some parental care. They keep the fertilized eggs and then later the hatched larvae in a pouch called the marsupia. They keep the larvae there for awhile, until a fish is nearby. When the fish is near, the females release the larvae, and the larvae will attach to the fish to complete development. After the larvae are released, they are independent of the mother and receive no more care. ("Status and Life History of the Three Assessed Mussels", 2007; Jennings, 2012; "Aridens confragosus", 2013)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female

How long do they live?

Many rock pocketbook mussels do not live past the larval stage, but if they reach adulthood, they can live for years. The exact lifespan for this species is not known, but other freshwater mussels can live from 5 years to more than 100 years. ("Freshwater Mussels of the Upper Mississippi River System", 2006; Jennings, 2012)

How do they behave?

Rock pocketbook mussels mostly stay in one spot, but they have a muscular body part called a foot that they can use to move around or attach themselves to the river bottom. Many juvenile mussels will crawl a good distance before finding a suitable habitat to settle down in. Crawling is accomplished by extending the foot, anchoring its tip with mucus or other substance, and then pulling the body forward. Adults do not move as much as juveniles. (Jennings, 2012; "Aridens confragosus", 2013)

How do they communicate with each other?

Rock pocketbook mussels can detect changes in light, though they cannot see the way humans do. They can also detect vibrations and physical touch. If something touches them, they will close their two shells to protect themselves. Larvae can respond to touch, light, and chemicals. (Arey, 1921; Jennings, 2012; Watters, 1995)

What do they eat?

Rock pocketbook mussels eat by filtering small particles of food out of the water. These particles are bacteria, protozoans, algae, and other bits of organic matter. Water enters their body through a tube called the incurrent siphon. The water moves through the gills, where oxygen and food particles are filtered out. The water leaves the body through another tube called the excurrent siphon, while food is brought from the gills to the mouth and then the stomach.

Parasitic larvae (glochidia) feed on blood and other nutrients from the fish that they attach to. (Arey, 1921; Jennings, 2012; "Aridens confragosus", 2013)

What eats them and how do they avoid being eaten?

Rock pocketbook mussels are eaten by mammals such as muskrats, raccoons, mink, and otter. Smaller individuals are also eaten by many species of fish. In response to a threat, Arcidens confragosus can shut its shells together, protecting the soft inner body parts. (Cummings and Mayer, 1992; Watters, 1995)

What roles do they have in the ecosystem?

Rock pocketbook mussels have important functions in aquatic environments. They are eaten by many different mammals and fish. They can also be infected with parasites such as trematode worms. They also can make water clearer by removing particles from it when they filter feed. (Jennings, 2012; Martinez, et al., 2002)

Species (or larger taxonomic groups) used as hosts by this species
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Rock pocketbook mussels do not cause any problems for humans.

How do they interact with us?

Rock pocketbook mussels can be used by researchers to study the state of an ecosystem. If mussels are successfully surviving in a river, then that means the water must be good and free of chemicals. If mussels disappear, it likely means that something is harming the habitat.

Native Americans and others use rock pocketbook mussels for food, and also in the building of tools, utensils, and pottery. Mussels are used for jewelry, as currency, and for trading. (Jennings, 2012)

  • Ways that people benefit from these animals:
  • food
  • body parts are source of valuable material

Are they endangered?

Rock pocketbook mussels are not an endangered species. (Jennings, 2012; Roe, 2002)


Meredith Schlenner (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Angela Miner (editor), Animal Diversity Web Staff.


Minnesota Department of Natural Resources. 2013. "Aridens confragosus" (On-line). Accessed March 23, 2013 at

2006. "Freshwater Mussels of the Upper Mississippi River System" (On-line). United States Fish and Wildlife Services. Accessed March 26, 2013 at

2003. "Reproductive Cycle in Mussels" (On-line). Upper Midwest Environmental Science Center. Accessed March 26, 2013 at

Environmental Protection Agency. Status and Life History of the Three Assessed Mussels. 2007. Accessed March 26, 2013 at

Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. Journal of Experimental Zoology, 33: 463-499.

Buchanan, A. 1980. Mussels (Naiades) of the Meramec River Basin: Issue 17 of Aquatic Series. Columbia, Missouri: Missouri Department of Conservation.

Cummings, K., C. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Champaign, Illinois: Illinois Natural History Survey Manual 5.

Jennings, S. 2012. "Needs in the Management of Native Freshwater Mussels in the National Park System" (On-line). Accessed March 26, 2013 at

Jirka, K., R. Neves. 1992. Reproductive Biology of Four Species of Freshwater Mussels (Mollusca: Unionidia) in the New River, Virginia and West Virginia. Journal of Freshwater Ecology, 7: 35-44. Accessed March 26, 2013 at

Lefevre, G., C. Winterton. 1910. Reproduction and parasitism in the Unionidae. Journal of Experimental Zoology, 9: 79-115.

Martinez, D., D. Spooner, T. Adornato, S. Dudding, C. Vaughn. 2002. Occurrence of the Rock Pocketbook Mussel, Arcidens confragosus (Bivalvia: Unionidae), in the Poteau and Deep Fork Rivers of Oklahoma. Proceedings of the Oklahoma Academy of Science, 84: 79-80. Accessed March 26, 2013 at

Murray, H., A. Leonard. 1962. Handbook of unionid mussels in Kansas: Issue 28 of University of Kansas Museum of Natural History. University of Kansas: Museum of Natural History 1962.

Roe, K. 2002. "Conservation Assessment for the Rock Pocketbook (Arcidens confragosus) Say, 1892" (On-line pdf). Accessed March 23, 2013 at

Watters, G. 1995. A guide to the freshwater mussels of Ohio. Columbus: Ohio Department of Natural Resources.

van der Schalie, H. 1938. The naiad fauna of the Huron River, in southeastern Michigan. Miscellaneous Publications of the Museum of Zoology, University of Michigan, 40: 1-83.

University of Michigan Museum of ZoologyNational Science Foundation

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Schlenner, M. 2014. "Arcidens confragosus" (On-line), Animal Diversity Web. Accessed May 25, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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