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Species Description

Delicate Spike

Elliptio arctata


Classification

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

Description

The Delicate Spike is a small freshwater mussel that measures less than 3.15 inches (80 mm) in length. The shell is thin and elliptical or oval-shaped. The periostracum (outer shell surface) is dull yellowish green in young specimens and dark brown in older specimens. The surface is often marked with green rays. The nacre (inner surface of shell) is dirty white or purplish in appearance.

Life Cycle

Some of the specific details about the complex life cycle of this mussel are not currently known, but the life history of Elliptio arctata is presumed to be similar to related species. Male Delicate Spike mussels release sperm into large rivers and creeks with moderate to strong currents. 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. Fish hosts have not been identified 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 transform into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sand or rock bottom of a river or creek.

Natural History

Delicate Spike 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 in the sand, cobble or gravel bottoms of large creeks and rivers with moderate to strong currents. This species is sometimes found in the bottom of rivers and creeks that are only 3 feet deep. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Delicate Spike 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

Historically, this species was found in Atlantic Slope drainages from North Carolina to the Savannah River in Georgia . It was also found within the Appalachicola River system and Alabama-Coosa River systems of Georgia , Florida , Alabama and Tennessee . It has also been found within the Pearl River system of Mississippi . However, this species is fairly rare and has possibly been extirpated from portions of its historical range. In Georgia , it may be found in portions of the Flint , Chattahoochee and Conasauga Rivers .

Conservation Status

The Delicate Spike is uncommon or rare within Georgia . Its population is dwindling within much of its historical range and it has possibly been extirpated from many portions of its range. Like many freshwater mussels, this species has likely been adversely affected by excess sedimentation, pollution and destruction of its habitat.

Similar Species

Identification of the Delicate Spike can be quite difficult and this species has often been confused with many other species of Elliptio. This rare mussel is best identified by professionals.