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Venustaconcha ellipsiformis

By Renee Sherman Mulcrone

Geographic Range

The ellipse is found in the upper Mississippi drainage from southern Michigan, Indiana, Illinois, central Wisconsin, southeastern Minnesota, and eastern Iowa. It is also found in tributaries of the Missouri and Mississippi River system in the northeastern part of the Ozark plateaus in Missouri west to the Neosho River of the Arkansas River drainage.

In Michigan V. ellipsiformis is found in the Grand, Kalamazoo, St. Joseph (Lake Michigan) and Saginaw Rivers. This species is essentially absent from the Lake Erie drainage. (Burch, 1975; Riusech and Barnhart, 2000; van der Schalie and van der Schalie, 1963)

Habitat

The ellipse is generally found in swift current in small to medium streams and small rivers with sand and/or gravel. (Cummings and Mayer, 1992; van der Schalie and van der Schalie, 1963; Watters, 1995)

  • Aquatic Biomes
  • rivers and streams

Physical Description

The ellipse is up to 7.6 cm (3 inches) long , and is oval and elliptical in shape. The shell is usually fairly solid and compressed. The anterior end is uniformly rounded, the posterior end bluntly pointed. The dorsal margin is slightly curved and the ventral margin is straight to slightly curved.

Umbos are low, raised only slightly above the hinge line and sit slightly to the anterior. The beak sculpture is fine, with three or four concentric double-loops.

The periostracum (outer shell layer) is smooth, except for growth lines. The shell is yellow to tan with numerous, thin rays. The rays are thinner and wavier toward the posterior ridge. Older specimens tend to be more brown.

On the inner shell, the left valve has two pseudocardinal teeth, which are triangular, rough, heavy and divergent. The two lateral teeth are short, straight to slightly curved, thick, and finely serrated. The right valve has one thick, triangular pseudocardinal tooth. Anterior to this tooth is usually a smaller (lamellar) tooth. The one lateral tooth is short and finely striated.

The beak cavity is shallow. The nacre is bluish-white, occasionally tinged with a rusty salmon color beneath the umbos. Often it is iridescent at the posterior end.

In Michigan, this species can be confused with the the rainbow and the rayed bean. The rays on the rainbow are often thicker and broken. The rainbow also has a longer hinge line and has finer teeth. The rayed bean is smaller and generally darker in color and more inflated. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    7.6 (high) cm
    2.99 (high) in

Development

Fertilized eggs are brooded in the marsupia (water tubes) up to 10 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; van der Schalie and van der Schalie, 1963)

Reproduction

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.

A study on Ore Creek, part of the Grand River system, found a majority mussels to be gravid from September to the following June. Males had well developed sperm in the spring, overlapping with periods when female eggs pass into ovisacs. (Lefevre and Curtis, 1912; van der Schalie and van der Schalie, 1963; Watters, 1995)

  • Breeding interval
    The ellipse breeds once in the warmer months of the year.
  • 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
  • pre-hatching/birth
    • provisioning
      • 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. Mantle flaps in the lampsilines are modified to attract potential fish hosts. How the ellipse attracts and 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)

Predation

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.

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, Venustaconcha ellipsiformis metamorphosed on the logperch, the black-sided darter,, the rainbow darter , the Iowa darter, the fantail darter, the johnny darter, the orangethroat darter, the redfin darter,, the greenside darter, the cardinal shiner the mottled sculpin, the slimy sculpin and the brook stickleback. (Hillegass and Hove, 1997; Hove and Anderson, 1997; Hove and Kurth, 1998; Riusech and Barnhart, 2000)

Species Used as Host

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

Venustaconcha ellipsiformis is considered threatened in Iowa, Kansas, Minnesota, and Wisconsin. In Indiana and Michigan this species is considered Special Concern. (Hove, 2004)

Other Comments

This species was formerly called Actinonaias ellipsiformis.

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

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

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

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.

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.

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 01, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR13.html#p16.

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., T. Anderson. 1997. Mantle-waving behavior and suitable fish hosts of the ellipse. Triannual Unionid Report, 11: 3. Accessed October 01, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR11.html#p3.

Hove, M., J. Kurth. 1998. Darters, sculpins, and stickelbacks serve as suitable hosts for Venustaconcha ellipsiformis glochidia. Triannual Unionid Report, 14: 8. Accessed October 01, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR14.html#p9.

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.

Riusech, F., M. Barnhart. 2000. Host suitability and utilization in Venustaconcha ellipsiformis and Venustaconcha pleasii (Bivalvia: Unionidae) from the Ozark Plateaus. Proceedings of the Captive Care, Propagation, and Conservation of Freshwater Mussels Symposium. March 6-8, 1998, Columbus, Ohio: 83-91. Accessed October 01, 2005 at http://courses.missouristate.edu/mcb095f/Documents/pdf_files/Riusech&Barnhart-00-FMS.pdf.

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

van der Schalie, H., A. van der Schalie. 1963. The distribution, ecology, and life history of the mussel, Actinonaias ellipsiformis (Conrad) in Micihgan. Occasional Papers of the Museum of Zoology, University of Michigan, 633: 1-17.

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