Tritogonia verrucosa

Tritogonia verrucosa (Rafinesque 1820)
 Pistolgrip


Tritogonia verrucosa, 7.03 cm shell length
Hatchet Creek (Clay County, Alabama)

Diagnosis

Historically, Tritogonia was a monotypic (but now defunct?) genus that has appears to be closely related to Quadrula (Serb et al. 2003).  Tritogonia verrucosa is very distinctive and not easily confused with other species.  Its shell is elongate and heavy and numerous pustules and corrugations are present.  In parts of the Alabama and Lower Coosa rivers, Tritogonia occurs with Plectomerus dombeyanus.  However, P. dombeyanus are more truncate and tend to only be sculptured on their posterior/dorsal shell surface.  Additionally, P. dombeyanus typically has a purple nacre whereas Tritogonia almost always has a white nacre.  In the Upper Alabama Drainage, Tritogonia can grow to >16 cm, the exterior of the shell is often heavily sculptured.  Tritogonia has been reported to be sexually dimorphic with females being shorter and more dorsally inflated than males (Parmalee and Bogan 1998).    

Ecology

Recent surveys found that Tritogonia verrucosa was common in large (>6th order) Coosa and Tallapoosa tributaries, especially in reaches with gravel or cobble substrate and moderate to high flows (Gangloff 2003).  Tritogonia were particularly abundant in the Terrapin and Big Canoe creek sub-basins and often were aggregated in large beds (Gangloff 2003).  Flathead catfish (Pylodictus olivaris) and yellow bullhead (Ameiurus natalis) are reported to be hosts for Tritogonia  (Parmalee and Bogan 1998).

Distribution

Tritogonia verrucosa is known from throughout the Mississippi, Mobile, and western Gulf drainages (Parmalee and Bogan 1993, Howells et al. 1996, Vidrine 1993).  It was historically abundant in the Mobile Drainage and occurred in the Alabama, Black Warrior, Cahaba, Coosa, and Tallapoosa rivers and their larger tributaries (Williams et al. 1992, Hurd 1974, van der Schalie 1938).

Status

Tritogonia verrucosa remains locally common in Alabama and extant populations are known from throughout the Mobile and Tennessee river basins.  Tritogonia verrucosa was the most abundant mussel found by recent surveys in the Conasauga River but nearly all mussels found were large, older specimens (Evans 2001). Recent surveys indicate that stable T. verrucosa populations are present throughout the Coosa and lower Tallapoosa drainages in Alabama (Gangloff 2003).  Tritogonia verrucosa populations are considered stable throughout its range (Williams et al. 1993).

References

Evans, R. D.  2001.  Historical and contemporary distributions of aquatic mollusks in the Upper Conasauga River system of Georgia and Tennessee.  M.S. Thesis, University of Tennessee Chattanooga, 277 p.

Gangloff, M. M.  2003.   The status, physical habitat associations, and parasites of freshwater mussels in the upper Alabama River Drainage, Alabama.  Ph.D. Dissertation, Auburn University. 237 p.

Hurd, J. C.  1974.  Systematics and zoogeography of the unionacean mollusks of the Coosa River Drainage of Alabama, Georgia and Tennessee.  Ph.D. Dissertation, Auburn University, 240 p.

Howells, R. G., R. W. Neck, and H. D. Murray.  1996.  Freshwater mussels of Texas.  Texas Parks and Wildlife, Austin, TX, 218 p.

Parmalee, P. W. and A. E. Bogan.  1998.  The freshwater mussels of Tennessee, University of Tennessee Press, Knoxville. 328 p.

Serb, J.M., J.E. Buhay, and C. Lydeard. 2003.  Molecular systematics of the North American freshwater bivalve genus Quadrula (Unionidae: Ambleminae) based on mitochondrial ND1 sequences.  Molecular Phylogenetics and Systematics 28(1):1-11.

van der Schalie, H. 1938.  The naiades (fresh-water mussels) of the Cahaba River in Northern Alabama.  Occasional Papers of the Museum of Zoology - University of Michigan 392:1-29.

Vidrine, M. F.  1993.  The historical distributions of freshwater mussels in Louisiana.  Gail Q. VIdrine Collectibles, Eunice, LA 225 p.

Williams, J. D., S. L. H. Fuller and R. Grace.  1992.  Effects of impoundments on freshwater mussels (Mollusca: Bivalvia: Unionidae) in the main channel of the Black Warrior and Tombigbee Rivers in Western Alabama.  Bulletin of the Alabama Museum of Natural History 13:1-10.

Williams, J. D., M. L. Warren, K. S. Cummings, J. L. Harris, and R. J. Neves.  1993.  Conservation status of freshwater mussels of the United States and Canada.  Fisheries 18:6-22.

Page Compiled by M. Gangloff, 21 July 2004.