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Strophitus undulatus

By Renee Sherman Mulcrone

Geographic Range

Creepers (Strophitus undulates) are widespread throughout the eastern half of the United States through the southern edge of Canada, although they are absent from Florida, Georgia and South Carolina. They are found in drainages including the Interior Basin, from central Texas to Lake Winnipeg, Canada and the Canadian Interior Basin in the Nelson River, from western Ontario to Saskatchewan. In the upper Atlantic drainage, they are found in the upper Savannah River system of South Carolina. This species is also found in the St. Lawrence River system and Nova Scotia. In Michigan, they are widespread throughout river systems in both the upper and lower peninsulas. (Burch, 1975)

Habitat

Creepers are found in a wide range of habitats, including headwaters, pools and large streams. They are probably scarcer in lower river reaches, and are generally absent from land-locked lakes. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Creepers are up to 10.2 cm long. Headwater specimens are generally smaller than those found in larger creeks. Their shell is elliptical or oval and may be thin or fairly thick in older individuals. Their anterior end is broadly rounded, their posterior end is bluntly pointed or truncated, their dorsal margin is rounded and their ventral margin is straight to slightly curved. Umbos are low and raised only slightly above the hinge line. Their beak sculpture has three to five v-shaped ridges. Their periostracum (outer shell layer) is green with rays, and brown to black in older individuals. On the inner shell, their left valve has a pseudo cardinal tooth, which is mainly a thickening of the hinge line. The tooth is located under the beak. Their right valve has a similar thickening of the hinge line, with the tooth anterior to the beak. Lateral teeth are absent. Their beak cavity is shallow. The nacre is cream colored or salmon in the center and bluish-white on the outer margin. In Michigan, this species can be confused with cylindrical papershells or giant floaters. However, cylindrical papershells are more cylindrical, with a less coarse beak sculpture and giant floaters have a less truncated posterior end, thinner hinges and less concentric beak sculpture. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    10.2 (high) cm
    4.02 (high) in

Development

Fertilized eggs are brooded in the marsupia (water tubes) up to 11 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 a glochidium, usually within a few hours. The glochidia 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; Oesch, 1984)

Reproduction

Increasing water temperatures stimulate male mussels to produce sperm and release it into the water, where it is taken up by nearby females. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)

Age to sexual maturity is unknown for creepers. Unionids are gonochoristic (sexes are separate) and viviparous. Glochidia, their larval stage, are released live from the female after they are fully developed. Among unionids, gametogenesis is initiated by increasing water temperatures. The general life cycle of unionids includes open fertilization. Males release sperm into the water, which is taken in by the females through their respiratory current. Their eggs are fertilized internally in their suprabranchial chambers and pass into water tubes of the gills, where they develop into glochidia. Creepers are long-term brooder. Gravid females have been observed in the Huron River from late July to the end of May. Glochidia are likely released at the end of May. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)

  • Breeding interval
    Creepers breed once in the warmer months of the year.
  • Breeding season
    In Michigan, the breeding season is probably early June to late July.
  • Range gestation period
    10 (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. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)

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

Lifespan/Longevity

Their age can be determined by looking at the annual rings on their shell. However, no demographic data has been recorded on this species, although members of family Unionidae generally have about a 10 year lifespan or more. (Haag, 2012; Winhold, 2004)

Behavior

In general, mussels are rather sedentary, although they may move in response to changing water levels and conditions. Although not thoroughly documented, mussels may vertically migrate to release glochidia and spawn. (Oesch, 1984)

Home Range

The home range size is not known for this species.

Communication and Perception

Most bivalve sensory organs are located in the middle lobe of the mantle edge. Paired statocysts, which are fluid filled chambers with a solid granule or pellet (a statolity) are in the mussel's foot and help the mussel with georeception or orientation. Mussels are heterothermic, and are therefore sensitive and responsive to temperature. Unionids may have some form of chemical reception to recognize fish hosts, although their method of host recognition is not known. Glochidia respond to touch, light and some chemical cues. In general, when touched or introduced to a fluid, they respond by clamping shut. (Arey, 1921; Brusca and Brusca, 2003; Watters, 1995)

Food Habits

In general, unionids are filter feeders. 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 directed to the mouth. Mussels have been cultured on algae, but may also ingest bacteria, protozoa and other organic particles. The parasitic glochidial stage absorbs blood and nutrients from hosts after attachment. Mantle cells within the glochidia feed on the host’s tissue through phagocytocis. (Watters, 1995)

Predation

In general, unionids are preyed on by muskrats, raccoons, minks, North American river otters and some birds. Juveniles are probably also consumed by freshwater drums, sheepsheads, lake sturgeon, spotted suckers, redhorses and pumpkinseeds. (Cummings and Mayer, 1992; Watters, 1995)

Ecosystem Roles

Creeper glochidia are unique in that they may metamorphose without using a fish host. Early research suggested that creepers did not use fish hosts in the wild, however, more recent evidence has shown they use several fish hosts including channel catfishes, black bullheads, yellow bullheads, burbots, plains killifishes, bluegills, pumpkinseeds, black crappies, white crappies, green sunfishes, rock bass, smallmouth bass, largemouth bass, common shiners, common stonerollers, river chubs, creek chubs, blacknose daces, longnose daces, northern redbelly daces, bluntnose minnows, fathead minnows, spotfin shiners, sand shiners, spottail shiners, central mudminnows, banded darters, fantail darters, rainbow darters, Iowa darters, johnny darters, slenderhead darters, logperches, blackside darters, yellow perches, walleyes and brook sticklebacks. Unionid mortality and reproduction is affected by unionicolid mites and monogenic trematodes feeding on their gill and mantle tissue, likewise parasitic chironomid larvae may destroy up to half of the mussels' gill. (Cummings and Mayer, 1992; Hillegass and Hove, 1997; Hove, et al., 1997; van Snik Gray, et al., 1999; Van Snik Gray, et al., 2002; Watters, 1995; Watters, et al., 1998)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Mussels are ecological indicators. Their presence in a water body usually indicates good water quality. (Farris and Van Hassel, 2007)

Economic Importance for Humans: Negative

There are no significant negative impacts of mussels on humans.

Conservation Status

Creepers are listed as a threatened species in Iowa and a species of special concern in Massachusetts. They are also a species of concern in Rhode Island and South Carolina. (Hove, 2004)

Contributors

Renee Sherman Mulcrone (author).

Glossary

Nearctic

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.

chemical

uses smells or other chemicals to communicate

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

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

ectothermic

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

fertilization

union of egg and spermatozoan

filter-feeding

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.

freshwater

mainly lives in water that is not salty.

heterothermic

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

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

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.

motile

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.

parasite

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

phytoplankton

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

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

vibrations

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

visual

uses sight to communicate

viviparous

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

References

Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. Journal of Experimental Zoology, 33: 463-499.

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.

Cliff, M., M. Hove, M. Haas. 2001. Creeper glochidia appear to be generalists. Ellipsaria, 3: 19-20.

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.

Farris, J., J. Van Hassel. 2007. Freshwater Bivalve Ecotoxicology. Pensacola: Society of Environmental Toxicology and Chemistry.

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. 2012. North American Freshwater Mussels: Natural History, Ecology, and Conservation. New York: Cambridge University Press.

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.

Hillegass, K., M. Hove. 1997. Suitable fish hosts for glochidia of three freshwater mussels: strange floater, ellipse, and snuffbox. Triannual Unionid Report, 13: 25.

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. 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., R. Engelking, M. Peteler, E. M. Peterson, A. R. Kapuscinski, L. A. Sovell 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.

Lefevre, G., W. Curtis. 1912. Experiments in the artificial propagation of fresh-water mussels. Proceedings of the International Fishery Congress, Washington. Bulletin of the Bureau of Fisheries, 28: 617-626.

Lefevre, G., W. Curtis. 1910. Reproduction and parasitism in the Unionidae . Journal of Experimental Biology, 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.

Strayer, D. 1980. The freshwater mussels (Bivalvia: Unionidae) of the Clinton River, Michigan, with comments on man's impact on the fauna, 1970-1978. Nautilus, 94: 142-149.

Strayer, D. 1979. Some recent collections of mussels from southeastern Michigan. Malacological Review, 12: 93-95.

Van Snik Gray, E., W. Lellis, J. Cole, C. Johnson. 2002. Host identification for Strophitus undulatus (Bivalvia: Unionidae), the creeper, in the upper Susquehanna River Basin, Pennsylvania. American Midland Naturalist, 147: 153-161.

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

Watters, G., S. O'Dee, S. Chordas. 1998. New Potential Hosts. Triannual Unionid Report, 15: 27-29.

Winhold, L. 2004. "Animal Diversity Web" (On-line). Family Unionidae . Accessed November 25, 2013 at http://animaldiversity.ummz.umich.edu/accounts/Unionidae/.

van Snik Gray, E., W. Lellis, J. Cole, C. Johnson. 1999. Hosts of Pyganodon cataracta (eastern floater) and Strophitus undulatus (squawfoot) from the Upper Susquehanna River basin, Pennsylvania. Triannual Unionid Report, 18: 6.

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.

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