Ochlockonee Moccasinshell

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Ochlockonee Moccasinshell

Medionidus simpsonianus

ListedMarch 16, 1998
DescriptionSmall mussel; shell is light brown to yellowish green, with dark green rays.
HabitatStable sandy and gravelly substrates in medium-sized streams to large rivers, often in areas swept free of silt by the current.
FoodFilter-feeder of phytoplankton and organic detritus.
ReproductionFemale siphons sperm from the water to fertilize her eggs, which hatch into parasitic larvae, which metamorphose into sedentary adults.
RangeFlorida, Georgia


The Medionidus simpsonianus (Ochlockonee moccasinshell) is a small species, generally under 2.2 in (5.5 cm) in length. It is slightly elongate-elliptical in outline, the posterior end obtusely rounded at the shell's median line and the ventral margin broadly curved. The posterior ridge is moderately angular and covered in its entire length with well developed, irregular ridges. Sculpture may also extend onto the disk below the ridge. Surface texture is smooth. The color is light brown to yellowish green, with dark green rays formed by a series of connected chevrons or undulating lines across the length of the shell. Internal characteristics include thin straight lateral teeth and compressed pseudo-cardinal teeth. There are two laterals and two pseudocardinals in the left valve and one lateral and one pseudocardinal in the right valve. The nacre is bluish white. The host fish for the Ochlockonee moccasinshell is unknown at this time. The lampsiline Ochlockonee moccasinshell probably uses darters as host fish, as do its congeners, the Alabama moccasinshell (Medionidus acutissimus ), Cumberland moccasinshell (M. conradicus ), and Gulf moccasinshell (M. penicillatus ).


Adult Ochlockonee moccasinshells are sedentary as adults. They siphon streamwater and filter phytoplankton and organic detritus as food. The female moccasinshells siphon water containing sperm to fertilize their eggs. The eggs hatch into larvae that are parasitic on fish. The larvae later metamorphose into sedentary adults.


The Ochlockonee moccasinshell inhabits stable sandy and gravelly substrates in medium-sized streams to large rivers, often in areas swept free of silt by the current.


The Ochlockonee moccasinshell was described from the Ochlockonee River, Calvary, Grady County, Georgia. This Ochlockonee River system endemic was known historically from the mainstem and the Little River. Museum records for this species sometimes numbered in the dozens of individuals at sites above Talquin Reservoir.

It was formerly known from eight sites. It is now known only from two sites, where there is no evidence of recruitment.

During the status survey, eight sites were sampled within the historic range of the Ochlockonee moccasinshell, including three of six (50%) known historical sites. Live individuals were found at two sites (one specimen at each site); one of these was a historic site. Another specimen was located in 1995 at a site previously sampled during the status survey. Only three live individuals are known to have been collected since 1974 despite concerted efforts by numerous investigators; none were juveniles.


Talquin Reservoir flooded about 12% of the river-ine habitat in the middle portion of the Ochlokonee river and the lower end of its largest tributary (the Little River). Preimpoundment records exist for the Ochlockonee moccasinshell at the upstream end of Talquin Reservoir, now absent downstream of the dam. This indicates that potential host fish movements may have been blocked.

Conservation and Recovery

The Ochlockonee moccasinshell is a critically endangered species, with only three specimens being observed since 1974 in spite of a significant search effort. The most pressing conservation need of this rare mollusk is the protection of its surviving areas of critical habitat from impoundment. The habitat must also be protected from other damages, such as pollution. The populations of the Ochlockonee moccasinshell should be monitored and additional ones searched for. Research should be undertaken into its ecological needs, with a view to developing management practices to maintain and improve its habitat.


U.S. Fish and Wildlife Service
Jacksonville Ecological Services Field Office
6620 Southpoint Drive South, Suite 310
Jacksonville, Florida 32216-0958
Telephone: (904) 232-2580
Fax: (904) 232-2404

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345


U.S. Fish and Wildlife Service. 16 March 1998. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Five Freshwater Mussels and Threatened Status for Two Freshwater Mussels From the Eastern Gulf Slope Drainages of Alabama, Florida, and Georgia." Federal Register 63(50): 12664-12687.