Despite the tiny size of this freshwater snail, the flat pebblesnail can be distinguished from other species in the Hydrobiidae family by its relatively large shell. It has two or three coils to its shell and the shell coils are, as its name indicates, flattened and oval in shape. This species can also be identified by the lack of a hole or depression in the centre of the shell and the lack of a distinct point to the shell (2). Snails in the Hydrobiidae family rarely have any colour to the shell and are often white (3).
Little is known about the biology of the flat pebblesnail, but, like other species in this family of freshwater gastropods (the Hydrobiidae), it is likely to feed on detritus and films of bacteria and algae found on the rocks in rivers (5).
The flat pebblesnail lays eggs in capsules, which are attached to hard surfaces within the river (4). After hatching, the juvenile snail, which measures 0.25 millimetres, starts grazing immediately (6). The life-cycle of this species appears to be completed in one year (4).
The flat pebblesnail is found only in central Alabama, USA. It is currently found at only two sites, in the Cahaba River in Shelby county and the Little Cahaba in Bibb County (2)(4). Historically, it had a larger distribution within these two rivers, as well as being found in the Coosa River (4).
The historical range of the flat pebblesnail has decreased by 90 percent as a result of numerous threats, largely created by human activity. Mining and dredging are two of the primary causes of flat pebblesnail’s decline, destroying and polluting the freshwater habitats on which this species so desperately relies. The creation of dams is another significant factor; in 1993 and 1996 studies failed to find a single flat pebblesnail in one Coosa River portion after two dams were developed upstream (4).
The US Fish and Wildlife Service lists the flat pebblesnail as Endangered and thus a major recovery plan was initiated in 2005 with the aim of re-classifying the species from Endangered to Threatened by 2015. As a result of the plan, the flat pebblesnail was bred in captivity and some of these captive-bred individuals have already been reintroduced into the species’ natural habitat (4). Other measures outlined in the recovery plan include protecting suitable habitat, developing public education programs and conducting further research on the flat pebblesnail (4). Implementing such conservation efforts, combined with close monitoring of the species’ progress, should hopefully avert further declines of this species.
Hershler, R. and Ponder, W.F. (1998) A Review of Morphological Characters of Hydrobioid Snails. Smithsonian Institute, Washington.
U.S. Fish and Wildlife Service. (2005) Recovery Plan for Six Mobile River Basin Aquatic Snails. US Fish and Wildlife Service, Jackson, Mississippi.
Clark, S. (2004) Hydrobiidae. In: Perez, K.E., Clark, S.A. and Lydeard, C. (Eds.) Showing Your Shells: A Primer to Freshwater Gastropod Identification. Freshwater Mollusk Conservation Society, Tuscaloosa, Alabama.
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