Cyclonaias tuberculata

Geographic Range

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)


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)

  • Aquatic Biomes
  • rivers and streams

Physical Description

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)

Umbos are low and only slightly raised above the hinge line. The beak sculpture has several wavy ridges. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

The periostracum (outer shell layer) has several pustules, and ridges on the dorsal wing. Younger specimens are yellowish to greenish brown, while older specimens tend to be more uniformly brown. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

On the inner shell, the left valve has two widely divergent, serrated, thin and low pseudocardinal teeth. The two lateral teeth are striated, and straight to slightly curved. The right valve has one heavy, triangular serrated pseudocardinal tooth with a small tooth on either side. The right, single lateral tooth is slightly curved and striated. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

The beak cavity is very deep. The nacre is almost always purple, and rarely white. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

In Michigan, this species can be confused with the pimpleback. The pimpleback usually has a prominent green ray, lacks a dorsal wing and purple nacre. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    12.7 (high) cm
    5.00 (high) in


Fertilized eggs are brooded in the marsupia (water tubes) up to three months, where they develop into larvae, called glochidia. The glochidia are then released into the water where they must attach to the gill filaments and/or general body surface of the host fish. After attachment, epithelial tissue from the host fish grows over and encapsulates the glochidium, usually within a few hours. The glochidium then metamorphoses into a juvenile mussel within a few days or weeks. After metamorphosis, the juvenile is sloughed off as a free-living organism. Juveniles are found in the substrate where they develop into adults. (Arey, 1921; Lefevre and Curtis, 1910)


Age to sexual maturity for this species is unknown. Unionids are gonochoristic (sexes are separate) and viviparous. The glochidia, which are the larval stage of the mussels, are released live from the female after they are fully developed.

In general, gametogenesis in unionids is initiated by increasing water temperatures. The general life cycle of a unionid, includes open fertilization. Males release sperm into the water, which is taken in by the females through their respiratory current. The eggs are internally fertilized in the suprabranchial chambers, then pass into water tubes of the gills, where they develop into glochidia.

The purple wartyback is a short-term brooder. On the Huron River, it was gravid from late May to early August. It likely spawns in early May. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)

  • Breeding interval
    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 brood fertilized eggs in their marsupial pouch. The fertilized eggs develop into glochidia. There is no parental investment after the female releases the glochidia.

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


The age of mussels can be determined by looking at annual rings on the shell. However, no demographic data on this species has been recorded.


Mussels in general are rather sedentary, although they may move in response to changing water levels and conditions. Although not thoroughly documented, the mussels may vertically migrate to release glochidia and spawn. Often this species is buried under the substrate. (Oesch, 1984)

Communication and Perception

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

Mussels are heterothermic, and therefore are sensitive and responsive to temperature.

Unionids in general may have some form of chemical reception to recognize fish hosts. How the purple wartyback attracts or if it recognizes its fish host is unknown.

Glochidia 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)

Food Habits

In general, unionids are filter feeders. The mussels use cilia to pump water into the incurrent siphon where food is caught in a mucus lining in the demibranchs. Particles are sorted by the labial palps and then directed to the mouth. Mussels have been cultured on algae, but they may also ingest bacteria, protozoans and other organic particles.

The parasitic glochidial 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)


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)

Unionid mortality and reproduction is affected by unionicolid mites and monogenic trematodes feeding on gill and mantle tissue. Parasitic chironomid larvae may destroy up to half the mussel gill. (Cummings and Mayer, 1992; Watters, 1995)

Ecosystem Roles

Fish hosts are determined by looking at both lab metamorphosis and natural infestations. Looking at both is necessary, as lab transformations from glochidia to juvenile may occur, but the mussel may not actually infect a particular species in a natural situation. Natural infestations may also be found, but glochidia will attach to almost any fish, including those that are not suitable hosts. Lab transformations involve isolating one particular fish species and introducing glochidia either into the fish tank or directly inoculating the fish gills with glochidia. Tanks are monitored and if juveniles are later found the fish species is considered a suitable host.

In lab trials, Cyclonaias tuberculata metamorphosed on the black bullhead, the yellow bullhead, the channel catfish, and the flathead catfish. These species generally co-exist with the purple wartyback, but no natural infestations have been observed. (Cummings and Watters, 2004; Hove, et al., 1994; Hove, 1997; Hove, M.C., Engelking, R.A., Peteler, M.E, et al., 1997)

Species Used as Host

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no significant negative impacts of mussels on humans.

Conservation Status

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)


Renee Sherman Mulcrone (author).



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


an animal that mainly eats decomposed plants and/or animals


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal that mainly eats plankton

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


uses touch to communicate


movements of a hard surface that are produced by animals as signals to others


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


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

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

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

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

Hove, M. 2004. "Links to each state's listed freshwater mussels, invertebrates, or fauna" (On-line). Accessed September 21, 2005 at

Hove, M. 1997. Ictalurids serve as suitable hosts for the purple wartyback. Triannual unionid report, 11: 4. Accessed October 01, 2005 at

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.