Critter Catalog

What do they look like?

Ebonyshells are circular, round, or oval-shaped mussels. They have thick shells with a noticeable point called a beak that fits into their round shape. They have smooth shells without bumps. They get their name because adults have dark shells. When they are older, the outside of their shell has brown or black curved lines coming out from the beak. When they are younger, the lines are more yellow or green. Ebonyshells look different from other mussels because they don't have don't have crosswise stripes like many other kinds of mussels. The insides of their shells are pearly white without stripes. Ebonyshells have seven teeth, and three of them are curved with jagged edges. Adults are usually 7.4 cm long but can be up to 10.2 cm long or more. (Cummings and Mayer, 1992; Illinois State Museum, et al., 2011; Wisconsin Dept. of Natural Resources, 2009)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range length

  10.2 (high) cm

  4.02 (high) in

• Average length

  7.4 cm

  2.91 in

Where do they live?

Ebonyshells live in the parts of the United States that drain into the Mississippi River. They live in the Mississippi River, the Minnesota River, the St. Croix River, the Illinois River, and the Ohio River. They used to live all the way from Minnesota to the Gulf of Mexico. However, a dam built in Iowa in 1913 stopped them from living in the northern half of the country. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Cummings and Mayer, 1992; Illinois State Museum, et al., 2011; Wisconsin Dept. of Natural Resources, 2009)

• Biogeographic Regions
• nearctic
  • native

What kind of habitat do they need?

Ebonyshells prefer to live in deep rivers with strong currents. They can also live in shallower waters and rivers with weaker currents. They are found in places with rocks, gravel, or sand on the bottom. Sometimes, they burrow down underneath the sand or mud. (Wisconsin Dept. of Natural Resources, 2009)

• These animals are found in the following types of habitat
• temperate
• freshwater

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• riparian

• Average depth

  1.8 m

  5.91 ft

How do they grow?

Ebonyshell eggs become larvae called glochidia before they are adults. The larvae live inside the gills of the mother. Then, females group the young together so they look like a worm. This attracts a fish, who eats the covering holding them together. The larvae end up in their gills, where they attach themselves. The most common fish in this relationship is skipjack herring. Other host fish are black crappie, white crappie, and largemouth bass. The bodies of the fish make a sac around the larvae, but it doesn't hurt them to have the larvae living on their bodies. The ebonyshells grow while attached to the fish. Later, they let go and settle into the bottom of the river. They grow during the warmer months and add to their shells. Later, they have their own eggs. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011; Wisconsin Dept. of Natural Resources, 2009)

• Development - Life Cycle
• metamorphosis

How do they reproduce?

Freshwater river mussels usually live close to each other on the bottom river, in groups called beds. Males release their reproductive cells into the water. Females nearby take in the reproductive cells to fertilize their eggs. The eggs grow and develop inside the gills of the mother. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011)

• Mating System
• polygynandrous (promiscuous)

Ebonyshells breed from June to September. One female ebonyshell can have tens of thousands of eggs in the same year. After the eggs hatch into larvae, they are released and attach to a host fish. Stuck to the host fish, they grow into young ebonyshells. This can take anywhere from a few days to a couple months. (Minnesota Dept of Natural Resources, 2011; Wisconsin Dept. of Natural Resources, 2009)

• Key Reproductive Features
• seasonal breeding
• sexual
• fertilization
  • internal
• ovoviviparous

• How often does reproduction occur?

  Ebonyshells spawn once every year.

• Breeding season

  Ebonyshells breed from June to September.

• Range number of offspring

  1000 to 50,000

• Average number of offspring

  10,000

• Range time to independence

  1 to 8 weeks

• Average time to independence

  4 weeks

Females protect their eggs inside their gills until they hatch into larvae. After the mothers release the eggs, neither one of the parents invests time or energy in the larvae. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011)

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

How long do they live?

Ebonyshells usually live 10 to 40 years, but can live to be more than 100 years old. Like trees, scientists can tell how old they are by counting the number of rings on the outside of their shells. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011)

• Range lifespan
  Status: wild

  100 (high) years

• Average lifespan
  Status: wild

  75 years

• Typical lifespan
  Status: wild

  10 to 40 years

How do they behave?

Ebonyshells mostly live alone. They might live close to many other ebonyshells, but they don't interact with each other. One of their only interactions is when females lure host fish by sticking them together so they look like worms. If a predator comes near ebonyshells, they seal themsleves shut and either burrow into the river bottom of shoot jets of water. The jets of water help them move or distract the predator. They also move by drifting in the current, or using their foot. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011)

• Key Behaviors
• motile
• sedentary

Home Range

Scientists don't know the exact size of the area where ebonyshells live. Most mussels don't move very much after they grow into adults.

How do they communicate with each other?

Ebonyshells cannot communicate very much. Females lure host fish for their larvae by putting them together to look like worms. They also react to touch, probably from predators. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011)

• Communication Channels
• tactile
• chemical

• Perception Channels
• tactile
• chemical

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 algae, plankton, small insects and worms, and rotting bits of dead plants and animals. (Cummings and Mayer, 1992; Minnesota Dept of Natural Resources, 2011)

• Primary Diet
• herbivore
  • algivore
• omnivore
• planktivore
• detritivore

• Plant Foods
• algae
• phytoplankton

• Other Foods
• detritus
• microbes

• Foraging Behavior
• filter-feeding

What eats them and how do they avoid being eaten?

Mussels are often eaten by raccoons, river otters, muskrats, herons and egrets, and some larger fish. Ebonyshells are camouflaged by their dark shells. Their hard thick shells are kept tightly closed using their muscles, which also protects them from predators. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Minnesota Dept of Natural Resources, 2011)

• These animal colors help protect them
• cryptic

• Known Predators

  • raccoons (Procyon lotor)
  • river otters (Lontra canadensis)
  • muskrats (Ondotra zibethicus)
  • herons and egrets (Ardeinae)
  • larger fish (Actinopterygii)

What roles do they have in the ecosystem?

Ebonyshells clean the water when they filter it. If they live in a particular spot, the water is probably good for other animals like fish and birds, too. Ebonyshell larvae grow inside Skipjack herrings, black crappies, white crappies, and largemouth bass. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011)

Do they cause problems?

There are no known negative impacts of ebonyshells on humans.

How do they interact with us?

The shells of ebonyshells were used to make pearl buttons in the 1900s so often that they almost became extinct in some places. People used to eat them, but stopped because they are so much more bitter than ocean mussels. Today, they are used to make pearls. They are also used for cancer research, because mussels don't get cancer. They are also a good sign that water is clean, and they clean the water when they filter it. People are now working to protect the habitats of ebonyshells by preserving rivers, protecting them from sand and gravel mining, and building passages for them to go through dams along the river. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Wisconsin Dept. of Natural Resources, 2009)

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

Are they endangered?

Ebonyshells are endangered in Wisconsin and Missouri. They are threatened in Illinois and Ohio, and considered special interest in Illinois and Minnesota. ("United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels", 2011; Cummings and Mayer, 1992; Illinois State Museum, et al., 2011; Minnesota Dept of Natural Resources, 2011; Wisconsin Dept. of Natural Resources, 2009)

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Contributors

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

References

United States Fish and Wildlife Service. United States Fish and Wildlife Service: Endangered Species: America's Mussels: Silent Sentinels. Unknown. Online: United States Fish and Wildlife Service. 2011. Accessed April 30, 2011 at http://www.fws.gov/midwest/endangered/clams/mussels.html.

Cummings, K., C. Mayer. 1992. "Fusconaia ebena" (On-line). Field guide to freshwater mussels of the Midwest. Illinois Natural History Survey Manual 5. Accessed July 21, 2011 at http://www.inhs.illinois.edu/animals_plants/mollusk/musselmanual/page42_3.html.

Illinois State Museum, , Havana Public Library District, Meredosia River Museum. 2011. "Ebony Shell" (On-line). Harvesting the River. Accessed July 11, 2011 at http://www.museum.state.il.us/RiverWeb/harvesting/harvest/mussels/species/ebonyshell.html.

Minnesota Dept of Natural Resources, 2011. "Fusconaia ebena (I. Lea, 1831)" (On-line). Minnesota Dept. of Natural Resources Rare Species Guide. Accessed July 21, 2011 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=IMBIV17060.

Wisconsin Dept. of Natural Resources, 2009. "Ebony Shell (Fusconaia ebena)" (On-line). Endangered Resources Program Species Information. Accessed July 07, 2011 at http://dnr.wi.gov/org/land/er/biodiversity/index.asp?mode=info&Grp=19&SpecCode=IMBIV17060.