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Species Description

Rayed Creekshell

Anodontoides radiatus


Classification

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

Description

The Rayed Creekshell is a small freshwater mussel that usually reaches 3.0 inches (75 mm) in length. It has a smooth, thin shell that is nearly oval in shape. The periostracum (outer shell surface) is brownish to olive brown and adorned with prominent dark green rays. The nacre (inner surface of the shell) is bluish white and sometimes marked with light yellow spots.

Life Cycle

Some of the specific details about the complex life cycle of this rare mussel are not currently known, but the life history of Anodontoides radiatus is presumed to be similar to related species. Male Rayed Creekshell mussels release sperm into small to medium-sized creeks and rivers with slow to moderate 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, gravel or mud bottom of a creek or river.

Natural History

Rayed Creekshell 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 or buried in the sand, mud or gravel bottoms of creeks and rivers with slow to moderate currents. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Rayed Creekshell 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 Rayed Creekshell was historically found in Gulf Coast drainages, from the Apalachicola-Chattahoochee-Flint (ACF) River system of Georgia , Alabama and Florida to the Tickfaw River system of Louisiana . In western Georgia , it may sporadically be found in portions of the Flint and Chattahoochee Rivers .

Conservation Status

This freshwater mussel is Rare and Imperiled in Georgia . Although historical collections reveal that this mussel was probably always rare in much of its range, recent surveys have found that the population has declined further and the range has been reduced. The Rayed Creekshell is now found only sporadically throughout much of its range. It is usually only found in small numbers, especially in the Apalachicola-Chattahoochee-Flint River system. The reasons for these declines in distribution and population size are unknown, but like many freshwater mussels this species has likely been adversely affected by pollution, habitat degradation and excess sedimentation.

Similar Species

The Rayed Creekshell has been confused with the rare Southern Creekmussel (Strophitus subvexus) in the past by collectors and researchers. This rare mussel is probably best identified by professionals.