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Plethobasus cyphyus

What do they look like?

Sheepnose mussels are a medium-sized mussel with a somewhat puffy and long shell. Male and female sheepnose mussels have different shaped shells. Females have a round, shorter back end, while males are oval shaped. Sheepnose mussels are yellow to dark brown in color, with dark ridges. Their outer shell is smooth and shiny. The inner shell is white in color. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012; "Sheepnose (a freshwater mussel)", 2013; Rose, 1820; Sietman, 2003)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    13 (high) cm
    5.12 (high) in

Where do they live?

Plethobasus cyphyus, the sheepnose mussel, is found in large rivers across the Midwest and southeastern parts of the United States. Currently, it is found in Alabama, Illinois, Indiana, Iowa, Kentucky, Minnesota, Mississippi, Missouri, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and Wisconsin. (Wolf, et al., 2012)

What kind of habitat do they need?

The sheepnose mussel lives in a large variety of habitats in large river systems and streams. Sheepnose mussels are typically found in shallow areas with medium to fast water currents flowing over sand and gravel. Additionally, they have been found in areas containing mud, boulders, and in deep ruts. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012)

  • Aquatic Biomes
  • rivers and streams

How do they grow?

The life cycle of a sheepnose mussel begins when males release sperm into the water, and the sperm enters the female body to fertilize her eggs. The eggs stay in a pouch in the gills of the female, and they hatch there into larvae called glochidia. The glochidia stay in the pouch until the female releases them into the water, and they attach to a fish. Glochidia are parasites, and need to attach to a fish to be able to complete development. Sheepnose mussels attach to a variety of fish, such as sauger (Sander canadensis), creek chub (Semotilus atromaculatus), and spottail shiner (Semotilus atromaculatus). Over several weeks, the glochidia transforms into a juvenile mussel, all while attached to the host fish. As juvenile mussels, they drop off of the host and land on the river bottom, where they will grow into adult mussels. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012; Rose, 1820; Wolf, et al., 2012)

How do they reproduce?

To reproduce, male sheepnose mussels release their sperm into the water. The water carries the sperm away towards female mussels. The sperm enters the female body through a tube called the incurrent siphon. This usually happens in early summer, in response to the warmer water temperatures. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012; Wolf, et al., 2012)

Fertilization occurs inside the female after she takes the sperm out of the water. The eggs stay with the female and hatch inside her gills. After some development time, the female releases the larvae, called glochidia, into the water in a jelly-like mass called a conglutinate. The glochidia then attach to a host fish, which they are parasites on. Sheepnose mussels are likely not able to mate until they are several years old, after they have dropped off the fish and spent time on the river bottom. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012; Wolf, et al., 2012)

  • How often does reproduction occur?
    Plethobasus cyphyus breeds once a year.
  • Breeding season
    Sheepnose mussels breed in the early months of the summer season.
  • Range number of offspring
    Hundreds to Millions

Female sheepnose mussels provide parental care, while males do not. After fertilization, the eggs stay with the female in a pouch in her gills. The eggs hatch there into glochidia, and they remain there for awhile. They are then released into the water, where the mussels are independent and do not get any more parental care. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012)

How long do they live?

Sheepnose mussels can live for as long as 30 years. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012)

  • Range lifespan
    Status: wild
    30 (high) years

How do they behave?

Sheepnose larvae are parasites of fish while they are developing. Since they develop in the mother, the mother mussel pretends to be bait for a fish. When the fish comes close, thinking it is food and not a mussel, the mother releases the larvae and they attach to the fish. Juvenile and adult sheepnose mussels are able to move around by pushing themselves with a large muscular part called the foot. Adults do not move often, and they stay in one place for long periods of time. (Rose, 1820)

Home Range

How do they communicate with each other?

Sheepnose mussels can detect touch and chemicals. They will usually clamp shut if touched. Larvae also do this, when they clamp shut on a fish host. Mussels do not really communicate with each other. ("Sheepnose (a freshwater mussel)", 2013)

  • Other Communication Modes
  • mimicry

What do they eat?

Sheepnose mussels feed on tiny particles in the water, such as algae, bacteria, protozoans, and other organic matter. To do this, they filter feed. Water enters their bodies through a tube called the incurrent siphon. When the water reaches the gills, tiny hair-like projections called cilia move the food particles out of the gills and to the mouth and stomach. Once the water is filtered, it leaves the body through another tube called the excurrent siphon. (Rose, 1820)

What eats them and how do they avoid being eaten?

Muskrats (Ondatra zibehicus) are the largest predator of freshwater mussels. They drag the mussel out of the water, onto the shore where they try to break the shell with their teeth or they wait for the mussel shell to open by leaving the mussel out of the water, causing it to die. Other predators of freshwater mussels are freshwater fishes, crayfish, and humans. Crayfish (Cambarus bartonii) eat juvenile mussels.

To escape predators, sheepnose mussels bury themselves into the mud and gravel at the bottom of rivers and streams. They still have to get oxygen out of the water while they are buried though, so they leave their back end sticking out of the mud to still be able to bring water into their bodies. This makes it easier for predators to get to them, however. ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012)

What roles do they have in the ecosystem?

Sheepnose mussels play several roles in their ecosystems. They are a part of the food web, as they are eaten by many mammals and other animals. They feed on algae and plankton. Glochidia are parasites of several species of fish, including sauger (Sander canadensis), creek chub (Semotilus atromaculatus), and spottail shiner (Semotilus atromaculatus). ("Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang", 2012)

Species (or larger taxonomic groups) used as hosts by this species

Do they cause problems?

Sheepnose mussels do not cause any problems for humans.

How do they interact with us?

The shells of sheepnose mussels are sometimes used as jewelry. Humans have also used mussels for food, tools, and decorative purposes. In the 1890's, they were used to make pearl buttons, but people used so many mussels for this that they started to disappear from areas that made a lot of buttons. By the 1940's, plastic was used to make buttons instead of mussels. Sheepnose mussels can also be used by scientists to study the health of ecosystems. If mussels begin to die, scientists know that something is wrong in the habitat, such as pollution, and the mussel populations provide clues to study this. (Winhold, 2004)

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

Are they endangered?

Sheepnose mussels are an endangered species. One of the main reasons they are endangered is habitat destruction. Humans can change the rivers and streams these mussels live in by building dams and getting chemicals or pollution into the water. Another problem is that zebra mussels, an invasive mussel species, are taking over their habitat and using up resources (such as food and oxygen) before sheepnose mussels are able to. Federal and state governments are carrying out research on sheepnose mussels to get as much information as they can about the mussel populations, and to find ways to prevent these mussels from going extinct. Humans will need to be careful about how they change the environment and how that can affect the animals living there. ("Sheepnose (a freshwater mussel)", 2013)

Contributors

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

References

Department of the Interior, Fish & Wildlife Services. Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Sheepnose and Spectaclecase Mussels Throughout Their Rang. Docket No. FWS–R3–ES–2010–0050; 4500030113]. United States Fish & Wildlife Service: Daniel M. Ashe. 2012. Accessed March 19, 2013 at http://www.fws.gov/midwest/endangered/clams/sheepnose/pdf/FRFinalListRuleSheepnoseSpecMarch2012.pdf.

2008. "Federally Listed Endangered, Threatened and Candidate Species for Minnesota" (On-line). Minnesota Department of Agriculture. Accessed April 01, 2013 at http://www.mda.state.mn.us/news/publications/chemfert/endangeredlist.pdf.

2013. "Sheepnose (a freshwater mussel)" (On-line). United States Fish & Wildlife Service. Accessed March 19, 2013 at http://www.fws.gov/midwest/endangered/clams/sheepnose/SheepnoseFactSheetMarch2012.html.

Rose, D. 1820. "Plethobasus cyphyus" (On-line). Accessed March 24, 2013 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=IMBIV34030.

Sietman, B. 2003. "Field Guide to the Freshwater Mussels of Minnesota" (On-line). Minnesota Department of Natural Resources. Accessed April 01, 2013 at http://files.dnr.state.mn.us/eco/nhnrp/mussel_survey/mussel_guide_sample.pdf.

Winhold, L. 2004. "Unionidae" (On-line). Animal Diversity Web. Accessed April 01, 2013 at http://animaldiversity.ummz.umich.edu/accounts/Unionidae/.

Wolf, K., M. Hove, B. Sietman, S. Boyer, D. Hornbach. 2012. Additional Minnows and Topminnow Identified as Suitable Hosts for the Sheepnose, Phethobasus cyphyus (Rafinesque, 1820). Newsletter of the Freshwater Mollusk Conservation Society, 14/3: 7. Accessed April 01, 2013 at http://molluskconservation.org/EVENTS/ELLIPSARIA/EllipsariaSept2012.pdf#page=7.

 
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Dose, K. 2014. "Plethobasus cyphyus" (On-line), Animal Diversity Web. Accessed October 15, 2019 at http://www.biokids.umich.edu/accounts/Plethobasus_cyphyus/

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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