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Elliptio crassidens

What do they look like?

Elephant-ear mussels have thick, heavy shells shaped like triangles. The outside of their shells are smooth. When they are younger, their outer shells are reddish-brown with light green lines. When they are adults, their outer shells are brown or black. The inside of their shells are almost always purple, although a few have been found that are pink or white inside. The top shell is curved, but the bottom shell is only curved in younger mussels. The most pointed part of the shell, which called the beak, is flatter than in many other kinds of mussels. They have triangular teeth on their shells. Males and females are hard to tell apart, but sometimes females have outer gills that are thicker than their inner gills. ("Elephant Ear (Elliptio crassidens)", 1999; Hickman, Jr., et al., 2011; Minnesota Dept. of Nat. Resources, 2012; NatureServe, 2012)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    15 (high) cm
    5.91 (high) in
  • Average length
    10 cm
    3.94 in

Where do they live?

Elephant-ear mussels live in many parts of the United States and in some parts of Canada. In the U.S., they are found in the Midwest, the East, and some parts of the South. They live in and around the Escambia and Apalachicola Rivers in Florida, and in Alabama, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee, Virginia, West Virginia and Wisconsin. In Canada, they live in the provinces of Quebec and Ontario. They used to live in Iowa, Oklahoma and Pennsylvania, but are not found in these states anymore. ("Elephant Ear (Elliptio crassidens)", 1999; Anthony and Downing, 2001; Brim Box, et al., 2002; Cummings, 2012; Dawley, 1947; Gagnon, et al., 2006; Grier, 1922; Illinois Natural History Survey, 2011; Minnesota Dept. of Nat. Resources, 2012; NatureServe, 2012; Van Der Schalie and Van Der Schalie, 1950)

What kind of habitat do they need?

Elephant-ear mussels live in rivers that have mud, sand, gravel or rocks on the bottom. They are found in water that has medium or fast currents like large creeks, rivers, or sometimes in channels. (Brim Box, et al., 2002; Cummings, 2012; Dawley, 1947; Gagnon, et al., 2006; Minnesota Dept. of Nat. Resources, 2012; "Elephant-ear Mussel: Elliptio crassidens", 2011; Van Der Schalie and Van Der Schalie, 1950)

  • Aquatic Biomes
  • benthic
  • rivers and streams
  • Average depth
    0.5 - 3.0 m
    ft

How do they grow?

Eggs of elephant-ear mussels first develop into larvae, which are called glochidia. The glochidia attach to a host fish and develop into juvenile elephant-ear mussels. Juveniles are like small versions of adults. They start to grow when they break free from their hosts and fall to the bottom of the water. The middle layer of their bodies is always adding to their shells. The new layers of shell are added to the most pointed part of their shell, which is called an umbo. (Grier, 1922; Hickman, Jr., et al., 2011; Illinois Natural History Survey, 2011; Jirka and Neves, 1992; Minnesota Dept. of Nat. Resources, 2012; NatureServe, 2012)

How do they reproduce?

Elephant ear mussels have a short breeding season. Males release their reproductive cells into the water. Nearby females take in water with male reproductive cells to fertilize their eggs. (Hickman, Jr., et al., 2011; Illinois Natural History Survey, 2011; Jirka and Neves, 1992; Minnesota Dept. of Nat. Resources, 2012; "Elephant-ear Mussel: Elliptio crassidens", 2011; NatureServe, 2012)

Elephant-ear mussel eggs grow into larvae while living inside the outer gills of the females. They are only about the size of dust particles. Females release their larvae when a fish is nearby. The larvae attach themselves to the gills or fins of the fish using their valves. They live attached to the fish for several weeks, and then break free and fall to the bottom of the river. Then, the young burrow into the sand or rocks on the bottom and grow into adult mussels. (Anthony and Downing, 2001; Dawley, 1947; Hickman, Jr., et al., 2011; Illinois Natural History Survey, 2011; Jirka and Neves, 1992; Minnesota Dept. of Nat. Resources, 2012; "Elephant-ear Mussel: Elliptio crassidens", 2011; NatureServe, 2012; "Freshwater Mussels", 2012)

  • How often does reproduction occur?
    Elephant-ear mussels breed once yearly (or less often).
  • Breeding season
    Elephant-ear mussels breed from April or May to June or July.
  • Range number of offspring
    100's to 1000's
  • Range time to independence
    A few weeks to A few months
  • Range age at sexual or reproductive maturity (female)
    4 to 6 years
  • Range age at sexual or reproductive maturity (male)
    4 to 6 years

Male elephant-ear mussels don't invest time or energy into their young, except that they fertilize the eggs. The females give nutrients to the larvae, and they live in her gills for a few weeks or months. Then, the females release the larvae to attach to a host fish and don't have any more contact with them. (Cummings, 2012; Illinois Natural History Survey, 2011; Jirka and Neves, 1992; Minnesota Dept. of Nat. Resources, 2012; NatureServe, 2012)

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

How long do they live?

Scientists don't know specifically how long elephant-ear mussels live. Mussels can live a long time, from 20 to even 100 years. ("Freshwater Mussels", 2012)

How do they behave?

Elephant-ear mussels can move around, but spend most of their time staying in the same spot. They are often found in large groups, but scientists don't know how or why they they do this. They have a strong muscular foot which they use to move around on the bottom. They fill the foot with blood to make it stick out, and then use the foot to crawl forward or hold themselves in place. (Hickman, Jr., et al., 2011)

  • Range territory size
    A few (high) m^2

Home Range

Adult elephant ear mussels usually stay within a few meters on the bottom of the spot where they settled as young mussels. (Dawley, 1947; NatureServe, 2012)

How do they communicate with each other?

None of the senses of elephant-ear mussels are very strong. They also can sense touch, chemicals, and balance using the edges of the fleshy part of their bodies. They have a clump of cells called an osphradium which might help them get chemical signals or sense the flow of the water. Female elephant-ears communicate with the fish their larvae attach to by luring them to the group of their larvae. (Hickman, Jr., et al., 2011; "America's Mussels: Silent Sentinels (Midwest Region)", 2012)

What do they eat?

All mussels are filter feeders, meaning that they strain bits of food out of the water. They pull water through pores and into their gills using cilia, which look like tiny hairs. The bits of food get trapped in their gills and then mucous moves the food to their digestive system. This way, they eat bacteria, protozoans, algae, and plankton. (Anthony and Downing, 2001; Dawley, 1947; Gagnon, et al., 2006; Illinois Natural History Survey, 2011; Minnesota Dept. of Nat. Resources, 2012; "Elephant-ear Mussel: Elliptio crassidens", 2011; NatureServe, 2012; "America's Mussels: Silent Sentinels (Midwest Region)", 2012)

What eats them and how do they avoid being eaten?

Elephant-ear mussels are eaten by otters, raccoons, muskrats, herons and egrets, and various fish. Like other freshwater mussels, elephant-ears have muscular feet. This helps anchor them to the bottom so they aren't swept away by the current or tugged free by predators. They also have strong muscles that keep their shells closed. Their strong, dark shells help camouflage them with the rocks and protect their delicate inner tissues. ("America's Mussels: Silent Sentinels (Midwest Region)", 2012)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

When elephant-ear mussels group together in beds, they create habitat for fish and worms or insects. They clean the water around them because they filter the water when they eat. Young elephant-ear mussels attach themselves to skipjack herring as they grow. They use the herring to get food, but don't hurt them in the process. They are threatened by the introduction of zebra mussels. Zebra mussels take up their habitat, live on their shells, and get in the way of their normal functions. ("Elephant Ear (Elliptio crassidens)", 1999; Anthony and Downing, 2001; Cummings, 2012; Dawley, 1947; Illinois Natural History Survey, 2011; Minnesota Dept. of Nat. Resources, 2012; "Elephant-ear Mussel: Elliptio crassidens", 2011; NatureServe, 2012; "America's Mussels: Silent Sentinels (Midwest Region)", 2012)

  • Ecosystem Impact
  • creates habitat
  • parasite
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?

There are no known negative economic effects of elephant-ear mussels.

How do they interact with us?

Mussels filter out toxins from the water. Whether they live in a particular area can tell scientists about the health of the water system. Since mussels don't get cancer, studying them might help cancer research. Mussels were used by Native Americans to make tools and also for food. Thicker-shelled mussels were used to make buttons in the 1900s, and are now used to make pearls. (Anthony and Downing, 2001; Grier, 1922; "Elephant-ear Mussel: Elliptio crassidens", 2011; "America's Mussels: Silent Sentinels (Midwest Region)", 2012)

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

Are they endangered?

Elephant-ear mussels are endangered in Minnesota, Missouri and Wisconsin. They are threatened in Illinois. (Cummings, 2012; "Threatened and Endangered Mussels", 2006)

Contributors

Keely McCormick (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Renee Mulcrone (editor), Special Projects, Catherine Kent (editor), Special Projects.

References

U.S. Fish & Wildlife Service. 2012. "America's Mussels: Silent Sentinels (Midwest Region)" (On-line). U.S. Fish & Wildlife Service: Endangered Species. Accessed April 01, 2012 at http://www.fws.gov/midwest/endangered/clams/mussels.html.

Wisconsin Department of Natural Resources. Elephant Ear (Elliptio crassidens). PUB-ER-085-99. Madison, Wisconsin: Wisconsin Department of Natural Resources. 1999. Accessed July 06, 2012 at http://dnr.wi.gov/topic/EndangeredResources/Animals.asp?mode=detail&SpecCode=IMBIV14080.

Missouri Department of Conservation. 2011. "Elephant-ear Mussel: Elliptio crassidens" (On-line). Missouri Department of Conservation: Best Management Practices. Accessed July 06, 2012 at http://mdc.mo.gov/sites/default/files/resources/2010/08/9467_6413.pdf.

Virginia Department of Game and Inland Fisheries. 2012. "Freshwater Mussels" (On-line). Virginia.gov. Accessed April 02, 2012 at http://www.dgif.virginia.gov/wildlife/freshwater-mussels.asp.

U.S. Fish & Wildlife Service. 2006. "Threatened and Endangered Mussels" (On-line). U.S. Fish & Wildlife Service: Freshwater Mussels of the Upper Mississippi River System. Accessed July 06, 2012 at http://www.fws.gov/midwest/mussel/threatened.html.

U.S. Army Corps of Engineers. 2005. "What is a Freshwater Mussel?" (On-line). Engineer Research and Development Center. Accessed April 02, 2012 at http://el.erdc.usace.army.mil/mussels/freshwater.html.

Anthony, J., J. Downing. 2001. Exploitation trajectory of a declining fauna: a century of freshwater mussel fisheries in. Canadian Journal of Fisheries & Aquatic Sciences, 58: 2071–2090.

Brim Box, J., R. Dorazio, W. Liddell. 2002. Relationships between streambed substrate characteristics and freshwater mussels (Bivalvia:Unionidae) in coastal plain streams. Journal of the North American Benthological Society, 21/2: 253-260.

Cummings, K. 2012. "Elliptio crassidens" (On-line). IUCN Red List of Threatened Species. Accessed July 06, 2012 at http://www.iucnredlist.org/apps/redlist/details/188905/0.

Dawley, C. 1947. Distribution of aquatic mollusks in Minnesota. American Midland Naturalist, 38/3: 671-697.

Gagnon, P., W. Michener, M. Freeman, J. Brim Box. 2006. Unionid habitat and assemblage composition in coastal plain tributaries of Flint River (Georgia). Southeastern Naturalist, 5/1: 31-52.

Grier, N. 1922. Final report on the study and appraisal of mussel resources in selected areas of the upper Mississippi River. American Midland Naturalist, 8/1: 1-33.

Hickman, Jr., C., L. Kats, S. Keen, B. Ober. 2011. Integrated Principles of Zoology: Fifteenth Edition. New York, NY: McGraw-Hill.

Illinois Natural History Survey, 2011. "Elliptio crassidens (Lamarck, 1819) Elephant-ear" (On-line). Illinois Natural History Survey Prairie Research Institute. Accessed July 06, 2012 at http://www.inhs.illinois.edu/animals_plants/mollusk/musselmanual/page66_7.html.

Jirka, K., R. Neves. 1992. Reproductive biology of four freshwater mussels (Mollusca: Unionidae) in the New River, Virginia and West Virginia. Journal of Freshwater Ecology, 7/1: 35-44.

Minnesota Dept. of Nat. Resources, 2012. "Elliptio crassidens (Lamarck, 1819) Elephant-ear" (On-line). Minnesota Department of Natural Resources. Accessed July 06, 2012 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=IMBIV14080.

NatureServe, 2012. "Elliptio crassidens - (Lamarck, 1819) Elephantear" (On-line). NatureServe Explorer. Accessed July 06, 2012 at http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Elliptio+crassidens+.

Van Der Schalie, H., A. Van Der Schalie. 1950. The Mussels of the Mississippi River. American Midland Naturalist, 44/2: 448-466.

 
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McCormick, K. 2012. "Elliptio crassidens" (On-line), Animal Diversity Web. Accessed October 31, 2014 at http://www.biokids.umich.edu/accounts/Elliptio_crassidens/

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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