Toxolasma parvus

Toxolasma parvus (Barnes 1823)
Lilliput

Toxolasma parvus, 2.61 cm shell length
Opintlocco Creek, Macon County, Alabama

Diagnosis
 
The genus Toxolasma includes 8 nominal species, 5 of which have been reported from Alabama (Turgeon et al. 1998).  It is presently unclear which, if any, species besides Toxolasma parvus  occurredhistorically in the Mobile Basin.  Toxolasma corvunculus has been reported to be a Coosa River endemic but shells exhibit very little predictable variability. All Toxolasmas are small (<3 cm), dark-colored mussels with a relatively thick shell and distinctive (blade-like) pseudocardinal teeth.  T. parvus superficially resembles Villosa lienosa but may be differentiated by the presence of a prominent protrusion (or caruncle) on the mantle margin in females.  This bulge becomes enlarged in gravid females and is presumed to aid in attracting fish hosts.  In some parts of its range, T. parvus is hermaphroditic and sexual dimorphism is absent (R. Butler, USFWS pers. com.).  However, individuals found in recent Upper Alabama River Drainage surveys appeared to be dimorphic with females tending to be laterally inflated along the posterior shell margin in a typical lampsiline fashion.  

Ecology

Recent surveys found Toxolasma parvus in small, often intermittent streams throughout the lower Tallapoosa River Drainage (Gangloff 2003).  Toxolasma parvus are often found in lakes, along stream margins, and in intermittent streams and sloughs suggesting that this species is fairly tolerant of drought or emersion.  Fish hosts of T. parvus are reported to include several species of centrarchids (Watters 1994).

Distribution

Toxolasma parvus is a widespread species and is known to occur in the St. Lawrence, Mississippi and nearly all Gulf of Mexico drainages (Vidrine 1993, Parmalee and Bogan 1998).  It was historically present throughout the Mobile Drainage. 

Status

Recent surveys of the Upper Alabama River Drainage (Coosa and Tallapoosa Rivers UAD) found that Toxolasma parvus was restricted to Lower Tallapoosa River tributaries (Gangloff 2003).  Although Hurd (1974) found a large number of T. parvus in Hatchet Creek Gangloff (2003) did not find it in Hatchet Creek or elsewhere in the Coosa Drainage of Alabama.  Recent surveys in the Upper Coosa (Georgia) also failed to detect this species (Evans 2001).  Toxolasma parvus are present in other portions of the Alabama drainage including the Cahaba and Alabama rivers and their tributaries (McGregor et al. 1999, McGregor et al. 2000, M. Gangloff unpublished data).  Despite undergoing apparent dramatic declines in the UAD, Toxolasma parvus appears 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.

McGregor, S. W., T. E. Shepard, T. D. Richardson, and J. F. Fitzpatrick.  1999.  A survey of the primary tributaries of the Alabama and Lower Tombigbee rivers for freshwater mussels, snails, and crayfish.  Geological Survey of Alabama Circular 196, 29 p.

McGregor, S. W., P. E. O'Neil, and J. M. Pierson.  2000.  Status of the freshwater mussel (Bivalvia: Unionidae) fauna in the Cahaba River system, Alabama.  Walkerana 11: 215-238.

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

Turgeon, D. D., J. F. Quinn, A. E. Bogan, E. V. Coan, F. G. Hochenberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams.  1998.  Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks, second edition.  American Fisheries Society, Special Publication 26 Bethesda, Maryland.

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

Watters, G. T.  1994.  An annotated bibliography of the reproduction and propagation of the Unionoidea (Primarily of North America).  Ohio Biological Survey Miscellaneous Contributions 1, 158 p.

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, 20 August 2004.