Georgia Wildlife Web

Home Glossary Classification Conservation Status Regions of Georgia Fishes of Georgia Make a Donation

Species Description

Butterfly mussel

Ellipsaria lineolata


Classification

Phylum: Mollusca
Subphylum:
Class: Bivalvia
Order: Unionoida
Family: Unionidae

Description

The Butterfly mussel is a small to medium-sized freshwater mussel that is sexually dimorphic. Female specimens tend to be more inflated or swollen in appearance and generally measure less than 2.75 inches (70 mm) in length. Male Butterfly mussels are more compressed and larger, usually measuring less than 4.3 inches (110 mm) in length. The unique shell is triangular in shape. The periostracum (outer shell surface) is dull yellow or greenish and may be marked with broken green rays. These broken rays look like rows of "V"-shaped or rectangular blotches. The nacre (inner surface of the shell) is white.

Life Cycle

Some of the specific details about the complex life cycle of this mussel are not currently known, but the life history of Ellipsaria lineolata is presumed to be similar to related species. Male Butterfly mussels release sperm into the swift current of a medium to large-sized river. Sperm enters females through siphon-like regions and fertilization of eggs occurs within female shells. These fertilized eggs develop into special larva called glochidia. Glochidia continue to develop and are released into the water column when fully matured. The parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. The Green Sunfish (Lepomis cyanellus) and Freshwater Drum (Aplodinotus grunniens) have been identified as suitable host fish. The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae transform into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the gravel or sand bottom of a river.

Natural History

Butterfly mussel l arvae (glochidia) are parasitic upon tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult mussels are typically sessile and are found attached to the sand or gravel bottom of swiftly flowing rivers. This species has been found at depths of up to 20 feet. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Butterfly mussels bring water from their habitat into their shells through specialized regions that are similar to the true siphons of clams. The water is then filtered over its gills and food particles are trapped and eventually digested.

Range

The Butterfly mussel has a very broad range that covers the Alabama River system in the Southeast and Mississippi River drainages throughout the Midwest .

Conservation Status

The status of this species in Georgia is currently unknown. However; in several states within the Southeastern portion of its broad range, the Butterfly mussel is listed as vulnerable or rare. Like many freshwater mussels, this species has presumably been affected by habitat degradation, pollution and excess sedimentation.

Similar Species

Within its very limited range in Georgia , the Butterfly mussel is rather distinct. Its unique triangular shape and broken dark green rays distinguish it from other mussels in Georgia .