Georgia Wildlife Web

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

Species Description

Altamaha Spinymussel

Elliptio spinosa


Classification

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

Description

The Altamaha Spinymussel is a unique, medium to large-sized freshwater mussel that measures less than 4.3 inches (110 mm) in length. The periostracum (outer shell surface) is a shiny, greenish-yellow color in young specimens and deep brown in older specimens. The outer shell surface is decorated with one to five conspicuous spines of varying lengths, with each usually measuring between 0.4 and 1 inch (1-5 cm) in length. The nacre (internal layer of the shell) is pink or purplish in appearance.

Life Cycle

Many of the specific details about the complex life cycle of this rare mussel are not currently known, but the life history of Elliptio spinosa is presumed to be similar to related species. Male Altamaha Spinymussels release sperm into swiftly-flowing rivers. 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 required fish hosts are not currently known for this species. The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the coarse, sandy bottom of sandbars.

Natural History

Many of the details about the natural history of the Altamaha Spinymussel are not currently known, but they are believed to be similar to better known, related species. Larvae (glochidia) are parasitic upon tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult Altamaha Spinymussels are not as sessile or sedentary as most freshwater mussels. They apparently move about their sandbar habitat, but are often found buried 2 to 4 inches below the sandbar surface. The large spines of the Spinymussel are presumably used to anchor it to the shifting sand of sandbars within swiftly-flowing rivers. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Altamaha Spinymussels 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 the gills and food particles are trapped and eventually digested.

Range

The Altamaha Spinymussel is endemic to the Altamaha River and its tributaries within Georgia . This historic range included the Altamaha River and lower portions of the Ohoopee, Ocmulgee and Oconee Rivers of Georgia. However, recent surveys have raised speculation that it has been extirpated from the Ohoopee and Oconee Rivers . It is still found in lower numbers in the lower portion of the Ocmulgee River and middle and upper sections of the Altamaha River .

Conservation Status

is large, unique mussel may also have aided the dramatic decline in its population size.

Similar Species

There is not another freshwater mussel within Georgia that possesses large spines and is brown or greenish-yellow in appearance.