Critter Catalog

What do they look like?

The outside of the round pigtoe's shell is smooth, with a dark brown color that may have some green rays in adults. The shell is often more tan in juveniles. The inside of the shell is typically white, but at times can vary from pink to salmon colored. The shells of males and females are similar. Round pigtoe shells can differ depending on where they live. The shells of those mussels found in smaller rivers tend to be rounder and flatter. The opposite is true for those in larger rivers, having more triangular and thicker shells. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range length

  13 (high) cm

  5.12 (high) in

Where do they live?

Pleurobema coccineum, the round pigtoe mussel, is found in the eastern parts of the United States and Canada. This area ranges from Ontario, south to Alabama, and from South Dakota at its west end to New York at its easternmost end. It is also present in the Mississippi and Ohio River drainages, and Lake Michigan, Lake Huron, Lake St. Clair, and Lake Erie drainages. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Biogeographic Regions
• nearctic
  • native

What kind of habitat do they need?

The round pigtoe is primarily found in larger rivers, but can be found in smaller rivers. It lives in habitats that have sand, mud, and gravel at the bottom of the river, and fast moving waters. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

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

• Aquatic Biomes
• benthic
• rivers and streams

• Range depth

  0.9 to 6.1 m

  2.95 to 20.01 ft

How do they grow?

Males release sperm into the water, and the sperm gets carried to the female by the water current. Once females receive sperm from males, the eggs develop inside the female. The eggs hatch inside the female into larvae, called glochidia. Females keep the glochidia in their gills for awhile. Glochidia are parasites and need to attach to a fish to continue development. When a fish is near, the female releases the glochidia. If the glochidia do not attach to a host, they will die in a day or two. Once attached to the gills of the fish, the glochidia develop into juvenile mussels in 6 to 8 weeks. When this is complete, the juvenile mussels drop off the host fish onto the bottom of the river and grow into adult mussels. (Marzec, 2004)

• Development - Life Cycle
• metamorphosis

How do they reproduce?

To mate, male round pigtoe mussels release their sperm into the water. This is called spawning. The water carries the sperm to females downstream, where they take the sperm into their bodies through a tube called the incurrent siphon. Spawning occurs when the water temperatures get warm in the late spring and early summer. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Marzec, 2004; Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

The fertilized eggs are kept in the female's gills from mid-May through July. During this time, they develop into larvae called glochidia. The glochidia are parasites and need a host to attach to, so that they can complete development. Females release the glochidia all on the same day, usually in the middle of June, when there is a fish nearby that the glochidia can attach to. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Culp, et al., 2009; Marzec, 2004; Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• oviparous

• How often does reproduction occur?

  Pleurobema coccineum reproduces once yearly.

• Breeding season

  Reproduction takes place in spring and summer.

Female round pigtoes provide care for their offspring. They keep the fertilized eggs and then later the hatched larvae in their gills from mid-May through July. Once the females release the larvae, the larvae are independent and do not receive any more parental care. (Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

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

How long do they live?

Round pigtoe mussels likely live for about 20 years or more. (Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Average lifespan
  Status: wild

  20 years

How do they behave?

Round pigtoe mussels can move around with the use of their foot, which is a muscle that can be extended out of their shell. They bury the foot in the sand and use it to pull themselves along. Mussels do not move much though, spending most of their lives buried in the mud and gravel at the bottom of the rivers they live in. Many mussel species are often found living together in a large group called a mussel bed. (Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Key Behaviors
• parasite
• motile
• sedentary

How do they communicate with each other?

There is not much known about how round pigtoe mussels communicate or what sense they use. Most mussels are able to detect vibrations and light. Glochidia can also detect touch. (Winhold, 2004)

• Perception Channels
• visual
• tactile
• vibrations

What do they eat?

The round pigtoe eats small particles in the water, such as bacteria, protozoa, algae, and other organic matter. Water moves into the body of the mussel through a tube called the incurrent siphon, and then into the gills. Oxygen and the food particles are filtered out of the water, and the food is moved by small hairs called cilia to be eaten. The water then moves out of the body through another tube called the excurrent siphon. (Michigan State University Board of Trustees., 2007; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008)

• Primary Diet
• planktivore
• detritivore

• Plant Foods
• algae
• phytoplankton

• Other Foods
• detritus
• microbes

• Foraging Behavior
• filter-feeding

What eats them and how do they avoid being eaten?

The muskrat is the primary predator of round pigtoe mussels. Other common predators of adult mussels include mink, river otter, raccoon, striped skunk, hellbenders, turtles, fish, some species of birds, and humans. Their shells provide protection from predators, keeping the soft inner body parts covered. The mussels also bury themselves into the bottom of the river or lake to hide from predators. (Tyrrell and Hornbach, 1998; Winhold, 2004)

• Known Predators

  • muskrat (Ondatra zibethicus)
  • mink (Neovison vison)
  • otter (Lontra canadensis)
  • raccoon (Procyon lotor)
  • striped skunk (Neovison vison)
  • hellbenders (Cryptobranchus)
  • turtles (Testudines)

What roles do they have in the ecosystem?

The glochidia of the round pigtoe are parasites of several types of fish, including bluegill, spotfin shiner, bluntnose minnow and northern redbelly dace. Adult round pigtoes feed on microorganisms like bacteria, protozoans, and algae. Mussels are also eaten by many different predators. Other aquatic organisms may attach themselves to the shells of round pignose mussels and live there.

• Ecosystem Impact
• parasite

Do they cause problems?

Round pignose mussels do not cause any problems for humans.

How do they interact with us?

Scientists can study round pigtoe mussels and learn a lot about their environment. When an aquatic habitat is healthy, there are healthy mussels in it. If mussels start to disappear, it usually means that there is something wrong with the environment, such as pollution. Mussels can give scientists clues abou their ecosystem. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004; Marzec, 2004; Minnesota Department of Natural Resources, Division of Ecological Resources., 2008; Tyrrell and Hornbach, 1998)

• Ways that people benefit from these animals:
• research and education

Are they endangered?

The round pigtoe is considered an endangered or threatened species in several states, such as Iowa, Pennsylvania, Minnesota, and Michigan. Round pigtoes have disappeared from much of the Great Lakes due to the invasive zebra mussel, which is taking over the habitat. Habitat destruction and pollution are also reasons why these mussels are disappearing. In these areas, many people are making conservation efforts to protect these mussel populations. ("COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada", 2004)

• IUCN Red List

  Least Concern

• US Federal List

  No special status

• CITES

  No special status

Some more information...

Contributors

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

References

COSEWIC. COSEWIC assessment and status report on the round pigtoe Pleurobema sintoxia in Canada. CW69-14/398-2004E-PDF. Ottawa: Committee on the Status of Endangered Wildlife in Canada. 2004. Accessed March 26, 2013 at http://people.cst.cmich.edu/zanat1d/COSEWIC_Round_Pigtoe.pdf.

Culp, J., A. Shepard, M. McGregor. 2009. Fish Hosts and Conglutinates of the Pyramid Pigtoe (Pleurobema rubrum). Southeastern Naturalist, Vol. 8, No. 1: 19-22. Accessed April 28, 2013 at http://www.jstor.org/stable/25599292.

Cummings, K. & Cordeiro, J, 2012. "Pleurobema sintoxia" (On-line). The ICUN Redlist of Threatened Species. Accessed March 16, 2013 at http://www.iucnredlist.org/details/173061/0.

Marzec, M. 2004. "Host fish and life cycle of the round pigtoe mussel." (On-line). Accessed March 26, 2013 at http://realscience.breckschool.org/upper/research/2003-04photos/Research2004/MeggieMarzec.pdf.

Michigan State University Board of Trustees., 2007. "Round pigtoe" (On-line pdf). Accessed March 16, 2013 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=IMBIV35070.

Minnesota Department of Natural Resources, Division of Ecological Resources., 2008. "Rare Species Guide: An online encyclopedia of Minnesota's rare native plants and animals" (On-line). Accessed March 20, 2013 at www.dnr.state.mn.us/rsg.

Tyrrell, M., D. Hornbach. 1998. Selective Predation by Muskrats on Freshwater Mussels in 2 Minnesota Rivers. Journal of the North American Benthological Society, Vol. 17, No. 3: 301-310. Accessed April 28, 2013 at http://www.jstor.org/stable/1468333.

Winhold, L. 2004. "Unionidae" (On-line). Animal Diversity Web. Accessed March 27, 2013 at http://animaldiversity.ummz.umich.edu/accounts/Unionidae/.