Critter Catalog

What do they look like?

The purple wartyback is up to 12.7 cm (5 inches) long, and is round. The shell is fairly thick, heavy and compressed. The anterior end is rounded, the posterior end somewhat angled. The dorsal margin is straight to slightly rounded and the ventral margin is broadly rounded. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

Younger specimens are yellowish to greenish brown, while older specimens tend to be more uniformly brown. The nacre (inner shell layer) is almost always purple, and rarely white. In Michigan, this species can be confused with the pimpleback. One way to tell them apart is that the pimpleback usually has a prominent green ray. Also, the pimpleback does not have a dorsal wing or purple nacre.

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range length

  12.7 (high) cm

  5.00 (high) in

Where do they live?

The purple wartyback is found in the Mississippi drainage, the Lake St. Clair drainage, the Detroit River and Lake Erie.

In Michigan C. tuberculata is mainly found in rivers of the Lake Erie drainage and the Kalamazoo, St. Joseph, Thornapple and Grand Rivers of the Lake Michigan drainage. It has also been recorded in the Menominee River in the upper peninsula. (Burch, 1975; van der Schalie, 1938)

• Biogeographic Regions
• nearctic
  • native

What kind of habitat do they need?

Cyclonaias tuberculata is mainly found in rivers where definite riverine conditions with a stronger current exist. In Michigan and Ohio it may be found in smaller rivers. In the St. Joseph River, it was found in slower moving waters that were fairly clear. In general the purple wartyback is found in better quality streams. (Badra, 2004; van der Schalie, 1938; Watters, 1995)

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

• Aquatic Biomes
• rivers and streams

How do they grow?

Fertilized eggs are brooded in the marsupia (water tubes) up to three months. While in the tubes, they develop into larvae. After the larvae are fully developed, they are released into the water.

Larvae must attach to the gill filaments or another surface of the host fish in order to continue growing. After attachment, tissue from the host fish completely grows over the larva, usually within a few hours. The larva then metamorphoses into a juvenile mussel within a few days or weeks. After metamorphosis, the juvenile breaks off and becomes a free-living organism. Juvenile mussels are found in the river bottom where they develop into adults.

• Development - Life Cycle
• metamorphosis

How do they reproduce?

Age to sexual maturity for this species is unknown. Unionids have separate male and female individuals. They are viviparous, which means that fertilization and development take place within the female body and the developing embryo derives nourishment from the female. The mussel larve (called glochidia) are released live from the female after they are fully developed.

The purple wartyback is a short-term brooder. Males release sperm into the water. The sperm is taken in by the females through their respiratory current. The eggs are internally fertilized, then pass into water tubes of the gills, where they develop into larvae (glochidia). The purple wartyback breeds once in the warmer months of the year. On Michigan's Huron River, the sperm is probably released in early May. The development in the female occurs from late May to early August. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)

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

• How often does reproduction occur?

  The purple wartyback breeds once in the warmer months of the year.

• Breeding season

  In Michigan, the breeding season is probably early May.

• Range gestation period

  2.5 (high) months

Females incubate fertilized eggs in their marsupial pouch. The fertilized eggs develop into larvae (glochidia). There is no parental care after the female releases the larvae (glochidia).

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

How long do they live?

The age of mussels can be determined by looking at annual rings on the shell. However, nobody has gathered data on this species to know how long their average lifespan is.

How do they behave?

Mussels in general are rather sedentary, which means they don't move around very much. However, they may move in response to changing water levels and conditions. Some scientists believe that the mussels may vertically migrate to release glochidia and spawn, but this has not been thoroughly documented. Often this species is buried under the river bottom surface. (Oesch, 1984)

• Key Behaviors
• parasite
• motile
• sedentary

How do they communicate with each other?

The middle lobe of the mantle edge has most of a bivalve's sensory organs. Paired statocysts are in the mussel's foot. Statocysts are fluid filled chambers with a solid granule or pellet (a statolity). The statocysts help the mussel with georeception, or orientation.

Mussels are heterothermic. This means they are both sensitive to and responsive to temperature.

Unionids in general may have some form of chemical reception to recognize fish hosts. Scientists are not sure how the purple wartyback attracts its fish host, or if it recognizes its fish host.

Glochidia (larvae) respond to touch, light, and some chemical cues. In general, when touched or a fluid is introduced, they will respond by clamping shut. (Arey, 1921; Brusca and Brusca, 2003; Watters, 1995)

• Communication Channels
• chemical

• Perception Channels
• visual
• tactile
• vibrations
• chemical

What do they eat?

In general, unionids are filter feeders. This means that they feed by filtering tiny organisms or fine particles of organic material from currents of water that pass through. Mussels have been cultured on algae, but they may also ingest bacteria, protozoans and other organic particles.

The parasitic glochidial (larval) stage absorbs blood and nutrients from hosts after attachment. Mantle cells within the glochidia feed off of the host’s tissue through phagocytocis. (Arey, 1921; Meglitsch and Schram, 1991; Watters, 1995)

• 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?

Unionids in general are preyed upon by muskrats, raccoons, minks, otters, and some birds. Juveniles are probably also fed upon by freshwater drum, sheepshead, lake sturgeon, spotted suckers, redhorses, and pumpkinseeds. (Cummings and Mayer, 1992; Watters, 1995)

The lifespan and reproductive success of these animals is affected by unionicolid mites and monogenic trematodes. The mites and trematodes feeding on gill and mantle tissue of the mussels. Another problem is parasitic chironomid larvae. These larvae may destroy up to half of the mussel's gill. (Cummings and Mayer, 1992; Watters, 1995)

• Known Predators

  • muskrat Ondatra zibethicus
  • mink Neovison vison
  • raccoon Procyon lotor
  • otter Lontra canadensis
  • turtles Testudines
  • hellbenders Cryptobranchus
  • freshwater drum Aplodinotus grunniens
  • sheepshead Archosargus probatocephalus
  • lake sturgeon Acipenser fulvescens
  • shortnosed sturgeon Acipenser brevirostrum
  • spotted suckers Minytrema melanops
  • common red-horse Moxostoma
  • catfish Siluriformes
  • pumpkinseed Lepomis gibbosus

What roles do they have in the ecosystem?

The glochidia stage of the purple wartyback exists as a parasite on a fish. The glochidia can attach to almost any fish, but it will only transform to a juvenile if it attaches to a suitable host.

It is hard for scientists to tell exactly which fish are suitable hosts for purple wartybacks. They have to use both lab studies and collect samples from rivers. Scientists are not sure, but they think the black bullhead, the yellow bullhead, the channel catfish, and the flathead catfish are the likely host fish for the purple wartyback. (Cummings and Watters, 2004; Hove, et al., 1994; Hove, 1997; Hove, M.C., Engelking, R.A., Peteler, M.E, et al., 1997)

• Ecosystem Impact
• parasite

Do they cause problems?

There are no significant negative impacts of mussels on humans.

How do they interact with us?

Mussels are ecological indicators. Their presence in a water body usually indicates good water quality.

In some parts of the United States, purple wartyback mussels are harvested to be used as the "seed" for cultured pearls. This is not allowed in Michigan. Mussels have also been used for buttons. Michigan mussels were harvested for buttons in the 1920s and 30s.

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

Are they endangered?

Cyclonaias tuberculata is listed as Endangered in Wisconsin, Threatened in Illinois, Iowa and Minnesota, and Significantly Rare in North Carolina. In Michigan it is listed as Special Concern. The IUCN Red List considers this species Lower Risk, Near Threatened. (Hove, 2004)

The biggest threats to mussels are invasive species, siltation from dams, and overharvesting.

• IUCN Red List

  Lower Risk - Near Threatened
  More information

• US Federal List

  No special status

• CITES

  No special status

Contributors

Renee Sherman Mulcrone (author).

References

Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. J. Exp. Zool., 33: 463-499.

Badra, P. 2004. Special Abstract for Cyclonaias tuberculata (Purple wartyback). Lansing, MI: Michigan Natural Features Inventory. Accessed October 04, 2005 at http://web4.msue.msu.edu/mnfi/abstracts/aquatics/Cyclonaias_tuberculata.pdf.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Burch, J. 1975. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America. Hamburg, Michigan: Malacological Publications.

Cummings, K., C. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Champaign, Illinois: Illinois Natural History Survey Manual 5. Accessed August 25, 2005 at http://www.inhs.uiuc.edu/cbd/collections/mollusk/fieldguide.html.

Cummings, K., G. Watters. 2004. "Mussel/Host Data Base" (On-line). Molluscs Division of the Museum of Biological Diversity at the Ohio State University. Accessed September 24, 2005 at http://128.146.250.63/Musselhost/.

Graf, D. 2002. Historical biogeography and late glacial origin of the freshwater pearly mussel (Bivalvia: Unionidae) faunas of Lake Erie, North America. Occasional Papers of Mollusks, 6: 175-211.

Haag, W., M. Warren. 1997. Host fishes and reproductive biology of six freshwater mussel species from the Mobile Basin, USA. Journal of the North American Benthological Society, 16: 576-585.

Hoeh, W., R. Trdan. 1985. Freshwater mussels (Pelecypoda: Unionidae) of the major tributaries of the St. Clair River, Michigan. Malacological Review, 18: 115-116.

Hove, M.C., Engelking, R.A., Peteler, M.E, , Hove, M.C., Engelking, R.A., Peteler, M.E, Hove, M.C., Engelking, R.A., Peteler, M.E, Peterson, E.M., Kapuscinski, A.R., Sovell, L.A. and E.R. Evers. 1997. Suitable fish hosts for glochidia of four freshwater mussels. Conservation and Management of Freshwater Mussels II. Proceedings of a UMRCC Symposium, 16-18 October 1995, St. Louis, Missouri: 21-25. Accessed October 04, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/Meetings/Symp1995Abs.html.

Hove, M. 2004. "Links to each state's listed freshwater mussels, invertebrates, or fauna" (On-line). Accessed September 21, 2005 at http://www.fw.umn.edu/Personnel/staff/Hove/State.TE.mussels.

Hove, M. 1997. Ictalurids serve as suitable hosts for the purple wartyback. Triannual unionid report, 11: 4. Accessed October 01, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR11.html#p4.

Hove, M., R. Engelking, E. Evers, M. Peteler, E. Peterson.. 1994. Cyclonaias tuberculata host suitability tests. Triannual unionid report, 5.

Lefevre, G., W. Curtis. 1912. Experiments in the artificial propagation of fresh-water mussels. Proc. Internat. Fishery Congress, Washington. Bull. Bur. Fisheries, 28: 617-626.

Lefevre, G., W. Curtis. 1910. Reproduction and parasitism in the Unionidae. J. Expt. Biol., 9: 79-115.

Meglitsch, P., F. Schram. 1991. Invertebrate Zoology, Third Edition. New York, NY: Oxford University Press, Inc.

Oesch, R. 1984. Missouri naiades, a guide to the mussels of Missouri. Jefferson City, Missouri: Missouri Department of Conservation.

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