Elliptio complanata

Geographic Range

Mainly an Atlantic coast species, the eastern ellliptio is found in the Apalachicola river system, Altamaha River system of Georgia north to the St. Lawrence River system of Canada. In the Interior Basin it is found west to Lake Superior and within the Hudson Bay drainage.

In Michigan E. complanata is found from Cheboygan County north through the upper peninsula. In the lower peninsula the southernmost records were from Lake Huron. One historical record was from the Clinton River. (Burch, 1975; Matteson, 1948a; Matteson, 1948b)


The eastern elliptio is mainly found in stable shoals of lakes or river-lakes in the northern part of the lower peninsula and the upper peninsula. It was most abundant in substrates composed of clay mixed with marl and fine sand, but rarely in mud. Depths where it seemed most common were one to 1.6 m (3 to 5 feet). (Matteson, 1948c; van der Schalie, 1938)

  • Aquatic Biomes
  • rivers and streams
  • Range depth
    1.6 (high) m
    5.25 (high) ft

Physical Description

The eastern elliptio is up to 12.5 cm (5 inches) long , and is quadrate or rectangular in shape. The shell is heavy and compressed with an angular posterior ridge and prominent posterior slope. The anterior end is rounded, the posterior end rounded to bluntly pointed. The dorsal margin is straight and the ventral margin is straight to slightly curved.

Umbos are low, being raised only slightly above the hinge line. The beak sculpture has 5-6 ridges.

The periostracum (outer shell layer) is tan or brown, sometimes with green rays. Older specimens tend to be more brown or black.

On the inner shell, the left valve has two pseudocardinal teeth, which are triangular and rough. The two lateral teeth are straight to slightly curved and moderately long. The right valve has one triangular, rough pseudocardinal tooth, and one straight to slightly curved, long, lateral tooth.

The beak cavity is shallow. The nacre is purple, rose-colored or white.

In Michigan, this species can be confused with the spike. The eastern ellipse is slightly more rhomboidal, more compressed, and has a slightly more prominent posterior ridge. (Cordeiro, 2003; Nedeau, et al., 2000)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    12.5 (high) cm
    4.92 (high) in


Fertilized eggs are brooded in the marsupia (water tubes) up to one months, depending on environmental conditions, 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 glochida 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; Matteson, 1948c)


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 fertilized in the suprabranchial chambers, then pass into water tubes of the gills, where they develop into larvae, called glochidia. (Lefevre and Curtis, 1912; Watters, 1995)

  • Breeding season
    In Michigan, the breeding season is mid-July to August.
  • Average gestation period
    10 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


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 they are found buried under the substrate. (Oesch, 1984)

Communication and Perception

Three large, distinct ganglia make up the bilateral nervous system of a bivalve. Cerebropleural ganglia are anterior and give rise to the visceral (gut) ganglia and pedal (foot) ganglia.

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.

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 snuffbox attracts its main fish host, the logperch, is unknown. However, the mantle flaps are darkened and may resemble food for the logperch.

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. (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.

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 transformations 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.

Lab metamorphosis and natural infections of Elliptio complanata have been observed for the yellow perch and the banded killifish,.

In lab trials, Elliptio complanata metamorphosed on the green sunfish, the largemouth bass, the orangespotted sunfish, and the white crappie. (Cummings and Watters, 2004; Lefevre and Curtis, 1912; Matteson, 1948c; Matteson, 1955; Tedla and Fernando, 1969; Young, 1911)

Species Used as Host

Economic Importance for Humans: Positive

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

Conservation Status

This species is not on any federal or state lists.

Other Comments

Elliptio complanata is synonomous with Elliptio complanatus.

An detailed life history of this species was done by Max Matteson in the early 1940s in northern Michigan. (Matteson, 1948c)


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.

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.

Cordeiro, J. 2003. "Family Unionidae: Genus Elliptio" (On-line). Freshwater mussels of the New York metropolitan region and New Jersey, A guide to their identification, biology, and conservation. Accessed September 05, 2006 at http://cbc.amnh.org/mussel/elliptiogenustext.html.

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 25, 2005 at

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.

Matteson, M. 1948. The taxonomic and distributional history of the fresh-water mussel Elliptio complanatus (Dillwyn, 1817). Nautilus, 61: 127-132.

Matteson, M. 1948. The taxonomic and distributional history of the fresh-water mussel Elliptio complanatus (Dillwyn, 1817) (continued). Nautilus, 62: 13-1.

Matteson, M. 1948. Life history of Elliptio complanatus (Dillwyn, 1817). American Midland Naturalist, 40: 690-723.

Matteson, M. 1955. Studies on the natural history of the Unionidae. American Midland Naturalist, 53: 126-145.

Nedeau, E., M. McCollough, B. Swartz. 2000. The freshwater mussels of Maine. Augusta, Maine: Maine Dept. of Insland Fisheries and Wildlife.

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

Tedla, S., C. Fernando. 1969. Observations on the glochidia of Lampsilis radiata (Gmelin) infesting yellow perch, Perca flavescens (Mitchill) in the Bay of Quinte, Lake Ontario. Canadian Journal of Zoology, 47: 705-712.

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

Young, D. 1911. The implantation of the glochidium on the fish. Univerity of Missouri Bulletin Science Series, 2: 1-20.

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.