Villosa lienosa - Little Spectaclecase

Villosa lienosa, 5.74 cm shell length
Chewacla Creek, Lee County, Alabama

Diagnosis

The genus Villosa includes 4 species in the Mobile Basin.   All Villosas are typically small mussels (< 6 cm total length) with thin and dimorphic shells.  Mobile Basin Villosa species superficially resemble several other genera, most notably the sympatric Strophitus connasaugaensis and Lasmigona holstonia.  However, soft tissues can be readily used to differentiate Villosa from Strophitus connasaugaensis and Lasmigona holstonia.  The most obvious differences can be observed in gravid individuals; gravid Villosa have glochidia restricted to the posterior portion of the outer gill whereas L. holstonia and S. connasaugaensis use the entire gill to brood glochidia.  Additionally, the gill may become so distended that their darkened margins often protrude from the shell and may prevent the valves from completely closing.
 
In the Mobile Basin, V. lienosa is largely restricted to small-to mid-sized streams in the Alabama, Black Warrior, Cahaba, Tallapoosa, and Tombigbee river drainages.  It has occasionally been reported from the Coosa drainage but most of these records are likely attributable to the Coosa endemic  V. umbrans which it superficially resembles.  The periostracum of Villosa lienosa is typically dark and un-rayed and the shell is more elongate than that of V. umbrans. The periostracum of V. umbrans is usually a light brown or buff and the dorsal posterior tip of female shells often protrudes oddly from the posterior margin giving the shell a 'pinched' appearance.  Shell dimorphism in V. lienosa is more subtle than in V. umbrans but females are typically inflated laterally, especially in specimens from reservoirs. 

Ecology

In recent surveys, Villosa lienosa was the most wide-spread mussel encountered in the lower Tallapoosa River Drainage of Alabama (Gangloff 2003).  Villosa lienosa is typically found in sand or gravel substrate adjacent to flow refugia such as stream banks or in association with stable, entrained woody debris.  Similar flow refugia were found to be important in structuring mussel spatial distributions in Atlantic and Gulf Coastal drainage streams (Brim-Box and Mossa 1999, Strayer 1999).

Villosa lienosa appears can persist (and reproduce) at very low densities in highly unstable habitats, likely because it employs a visual lure (mantle flaps) to attract fish hosts (Haag and Warren 1998).  Villosa lienosa can tolerate periodic stream drying and was found in several intermittent Gulf Coastal Plain streams (Gangloff 2003).  In more stable bottomed and  permanently flowing sites, Villosa lienosa is often the numerically dominant mussel in small, Coastal Plain streams.  

Villosa lienosa were gravid from February through May in southeast Alabama (M. Gangloff, unpublished data).  Host fishes include centrarchids and ictalurids (Keller and Ruessler 1997).  In southeast Alabama, V. lienosa glochidia were found (in situ) on spotted bass (Micropterus punctulatus) as well as green and bluegill sunfish (Lepomis cyanellus, L. macrochirus respectively, Buntin et al. unpublished data).

Distribution

Villosa lienosa is widespread in the ACF, Mississippi, Mobile, and other Gulf river drainages.  It was likely historically widespread in streams of the Coastal Plain but this part of the Upper Alabama River Drainage is not well represented in museum collections.  Extant populations of V. lienosa are known throughout the Alabama, Black Warrior, Cahaba, Tallapoosa, and Tombigbee drainages (McGregor and Pierson 1999, McGregor et al. 1999, McGregor et al. 2000).  Villosa lienosa can tolerate reservoirs and is abundant in Lake Martin, an impoundment on the Tallapoosa River in east central Alabama.

Status

Villosa lienosa appears to be stable in the Mobile and adjacent Gulf drainages in Alabama and throughout its range (Williams et al. 1993, Gangloff 2003). 

References

Brim Box, J. and J. Mossa.  1999.  Sediment, land use and freshwater mussels: prospects and problems.  Journal of the North American Benthological Society 18:99-117.

Brim-Box, J. and J. D. Williams.  2000.  Unionid mollusks of the Apalachicola Basin in Alabama, Florida, and Georgia.  Bulletin of the Alabama Museum of Natural History 21, 143 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.

Haag, W. R. and M. L. Warren.  1998.  Role of ecological factors and reproductive strategies in
structuring freshwater mussel communities.  Canadian Journal of Fisheries and Aquatic Sciences 55:297-306.

Keller, A. E. and D. S. Ruessler.  1997.  Determination or verification of host fish for nine species of unionid mussels.  American Midland Naturalist 138:402-407.

McGregor, S. W. and J. M. Pierson.  1999.  recent freshwater mussel (Bivalvia: Unionacea) records from the North River system, Fayette and Tuscaloosa counties, Alabama.  Journal of the Alabama Academy of Sciences 70:153-161.

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.

Strayer, D. L.  1999.  Use of flow refuges by unionid mussels in rivers.  Journal of the North
American Benthological Society 18:468-476.

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.

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.