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Strophitus undulatus

By Renee Sherman Mulcrone

Geographic Range

The creeper is widespread throughout most of the eastern half of the United States through the southern edge of Canada, but absent in Florida, Georgia, and South Carolina. Drainages where it is found include 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 it is 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 this species is widespread throughout river systems in both the upper and lower peninsulas. (Burch, 1975)

Habitat

Strophitus undulatus is found in a wide range of habitats, from headwaters to pools to larger streams. It is probably more scarce in lower reaches of rivers, and is generally absent from land-locked lakes. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

  • Aquatic Biomes
  • rivers and streams

Physical Description

The creeper is up to 10.2 cm (4 inches) long. Headwater specimens are generally smaller than those found in larger creeks. The shell is elliptical or oval and ranges from being thin to fairly thick in older individuals. The anterior end is broadly rounded and the posterior end is bluntly pointed or truncated. The dorsal margin is rounded and the ventral margin is straight to slightly curved.

Umbos are low and raised only slightly above the hinge line. The beak sculpture has three to five v-shaped ridges.

The periostracum (outer shell layer) is green with rays, and brown to black in older individuals.

On the inner shell, the left valve has a pseudocardinal tooth which is mainly a thickening of the hinge line. The tooth is located under the beak. The right valve has a similar thickening of the hinge line, with the tooth anterior to the beak. Lateral teeth are absent.

The 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 the cylindrical papershell or giant floater. The cylindrical papershell in general is more cylindrical. The creeper has a beak sculpture that is more coarse. In general, the creeper generally has a more truncated posterior end than the giant floater. The hinge on the creeper is also generally thicker and has a more 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 stimulates male mussels to produce sperm and release it into the water column, where it is taken up by nearby females.

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.

Strophitus undulatus is a long-term brooder. Gravid females were observed on 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.

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

Lifespan / Longevity

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.

Behavior

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. (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 creeper recognizes its fish host is not known.

Glochidia respond to both 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. (Watters, 1995)

Predation

Unionids in general are preyed on 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.

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.

Strophitus undulatus glochidia are unique in that they may metamorphose without the use of a fish host. However, the glochidia have also metamorphosed on several species of fish in lab trials. No natural infestations on fish have been recorded. Species of fish that the S. undulatus glochidia have metamorphosed on include: channel catfish, black bullhead, yellow bullhead, burbot, plains killifish, bluegill, pumpkinseed, black crappie, white crappie, green sunfish, rock bass, smallmouth bass, largemouth bass, common shiner, common stoneroller, river chub, creek chub, blacknose dace, longnose dace, northern redbelly dace, bluntnose minnow, fathead minnow, spotfin shiner, sand shiner, spottail shiner, central mudminnow, banded darter, fantail darter, rainbow darter, Iowa darter, johnny darter, slenderhead darter, logperch, blackside darter, yellow perch, walleye and brook stickleback. (Hillegass and Hove, 1997; Hove, et al., 1997; van Snik Gray, et al., 1999; Watters, et al., 1998)

Creeper glochidia have been found on: channel catfish, black bullhead, yellow bullhead, burbot, plains killifish, bluegill, pumpkinseed, black crappie, white crappie, green sunfish, rock bass, smallmouth bass, largemouth bass, common shiner, common stoneroller, river chub, creek chub, blacknose dace, longnose dace, northern redbelly dace, bluntnose minnow, fathead minnow, spotfin shiner, sand shiner, spottail shiner, central mudminnow, banded darter, fantail darter, rainbow darter, Iowa darter, johnny darter, slenderhead darter, logperch, blackside darter, yellow perch, walleye and brook stickleback.

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

There are no significant negative impacts of mussels on humans.

Conservation Status

Strophitus undulatus is listed as threatened in Iowa and Special Concern in Massachusetts. It is also a Species of Concern in Rhode Island and South Carolina. (Hove, 2004)

Other Comments

Strophitus undulatus is synonomous (same species, but with a former different name) with S. rugosus.

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. J. Exp. Zool., 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.

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.

Hillegass, K., M. Hove. 1997. Suitable fish hosts for glochidia of three freshwater mussels: strange floater, ellipse, and snuffbox. Triannual Unionid Report, 13: 25. Accessed October 04, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR13.html#p16.

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. 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.

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.

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. Accessed October 04, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR15.html#p21.

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. Accessed October 04, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR18.html#p5.

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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