Gulf moccasinshell: Medionidus penicillatus
Genus/Species: Medionidus penicillatus
Common Name: Gulf moccasinshell
Federal Status: Endangered
FL Status: Federally-designated Endangered
FNAI Ranks: G2/S2 (Imperiled)
IUCN Status: CR (Critically Endangered)
The Gulf moccasinshell is a small freshwater mussel that can reach a length of 2.2 inches (5.5 centimeters). This species has an oval-shaped shell that is greenish-brown with marks of green rays on the outer shell and green or dark purple on the inner shell. The valves are thin and contain two teeth in the left valve and one in the right (University of Georgia 2008, Florida Natural Areas Inventory 2001).
The Gulf moccasinshell is a filter feeder (filters food out of water). This species’ diet primarily consists of plankton and detritus (dead organic matter).
Little is known about the reproduction of the Gulf moccasinshell. It is believed that males release sperm in the water and females receive the sperm through a siphon. Eggs are fertilized in the female’s shell and the glochidia (larvae) release into the water. The larvae attach to the gills or fins of a host fish to develop (University of Georgia 2008). When the larvae are developed they release from the fish and settle in their primary habitat.
Habitat and Distribution
The Gulf moccasinshell inhabits creeks and large rivers with moderate currents that have a sandy or gravel floor. This species is known to be found in Ecofina Creek and the Chipola River in northwest Florida, and the Flint River in southwest Georgia. It also may be found in the Choctawhatchee, Apalachicola, and Yellow rivers in northwest Florida (Florida Natural Areas Inventory 2001).
Freshwater mussels face a host of threats due to human development and increased populations. The main threat is the impoundment of fresh waterways. Waterways are impounded for reasons including for fresh water supply, flood control, and hydropower. Impounding waterways cause the water current’s velocity to decrease causing sediment to build up in the river and covering the mussels located in the substrate. Impoundments also cause habitat fragmentation, separating mussel populations and also individual mussels from algae and host fish (U.S. Fish & Wildlife Service 2006). River dredging also threatens to destroy freshwater mussel populations on the river floors. The Asian clam (Corbicula fluminea), an invasive species, can out-compete the Gulf moccasinshell for resources in its habitat (Florida Natural Areas Inventory 2001). Pesticide and chemical pollution poses a significant threat to mussels since they are filter feeders and may ingest chemicals directly from their habitat.
Conservation and Management
The Gulf moccasinshell is protected as an Endangered species by the Federal Endangered Species Act and as a Federally-designated Endangered species by Florida’s Endangered and Threatened Species Rule . It is one of the target species in a 7-species Federal Recovery Plan . Specific actions needed to recover the species include (USFWS 2003):
- Secure extant subpopulations and currently occupied habitats and ensure subpopulation viability.
- Search for additional subpopulations of the species and suitable habitat.
- Determine through research and propagation technology the feasibility of augmenting extant subpopulations and reintroducing or reestablishing the species into historical habitat.
- Develop and implement a program to evaluate efforts and monitor subpopulation levels and habitat conditions of existing subpopulations, as well as newly discovered, reintroduced, or expanding subpopulations.
- Develop and utilize a public outreach and environmental education program.
- Assess the overall success of the recovery program and recommend actions.
Other Informative Links
Florida Natural Areas Inventory
International Union for Conservation of Nature
University of Georgia
Printable version of this page
Florida Natural Areas Inventory. 2001. Field guide to the rare animals of Florida. http://www.fnai.org/FieldGuide/pdf/Medionidus_penicillatus.PDF
University of Georgia. (2008). Gulf Moccasinshell Medionidus penicillatus. Retrieved July 7, 2011, from Museum of Natural History: http://naturalhistory.uga.edu
U.S. Fish and Wildlife Service. 2003. Recovery Plan for Endangered Fat Three ridge (Amblema neislerii), Shinyrayed Pocketbook (Lampsilis subangulata), Gulf Moccasinshell (Medionidus penicillatus), Ochlockonee Moccasinshell (Medionidus simpsonianus), and Oval Pigtoe (Pleurobema pyriforme): and Threatened Chipola Slabshell (Elliptio chipolaensis), and Purple Bankclimber (Elliptoideus sloatianus). Atlanta, Georgia. 142 pp.
U.S. Fish & Wildlife Service. (2006, June 8). Current Threats. Retrieved July 7, 2011, from Freshwater Mussels : http://www.fws.gov/midwest/mussel/current_threats.html
Image Credit FWC