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Species Description

Inflated Spike

Elliptio purpurella


Classification

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

Description

The Inflated Spike is a small freshwater mussel that often measures only 1.6 to 2.0 inches (40-50 mm) in length. As its name suggests, the shell of this species is greatly inflated, giving it a swollen or deep appearance. The periostracum (outer shell surface) is brownish is color and is sometimes marked with broad, green rays. The nacre (interior surface of the shell) is purple 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 purpurella is presumed to be similar to related species. Male Inflated Spike mussels release sperm into streams. 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 host species for the Inflated Spike are not known at this time. 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 sand, clay or limestone rock bottom of a stream.

Natural History

Many of the details about the natural history of the Inflated Spike 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 mussels are typically sessile and are found attached or buried within the clay, sand or rocky bottom of streams. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Inflated Spikes 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

This species is endemic to the Appalachicola-Chattahoochee-Flint River Basin of Georgia, Florida and Alabama . The Inflated Spike was historically found within the Flint , Chattahoochee and Chipola Rivers of this region. However, recent surveys have only found this freshwater mussel in tributaries of the Flint River in western Georgia . These surveys suggest that it may be extirpated from the Chattahoochee River and Chipola River portions of its historical range.

Conservation Status

This mussel is listed as Rare and Imperiled within Georgia . Its range has been greatly reduced and it is currently only found within the state. Like many freshwater mussels, the Inflated Spike has presumably been adversely affected by habitat degradation, excess sedimentation and pollution.

Similar Species

Within the limited range of the Inflated Spike within Georgia , it is fairly distinct due to its combination of small size and greatly inflated shell.