Armored Snail

Pyrgulopsis pachyta

Description

The armored snail is a small annual, usually less than 0.16 in (4 mm) in length. The shell is ovate-conical with a pronounced thickness. The edge of the shell opening, or peristome, is complete. The male reproductive organ, called the verge, has a small raised gland on the ventral surface and two small glands along the left margin of the lobe on the tip.

It can be distinguished from other closely related species by the verge, and also shell characteristics. Shells of other species in the Pyrgulopsis have much thinner, almost transparent shells, and do not have complete peristome along the opening.

Behavior

Little is known about the armored snail. It is a freshwater snail that spends much of its time submerged under water amongst the vegetation.

Members of the genus prefer to be near a spring or a stream that emerges from the ground, natural pools, and marsh-like springs. They also concentrate in areas where there is stable temperature and chemistry, and a flow regime that characterizes headsprings.

Habitat

The armored snail is generally found among submerged tree roots and bryophytes along stream margins in areas of slow to moderate flow. Sometimes they are found in submerged detritus along pool edges.

Distribution

There are two populations of armored snail, one in Piney Creek and the other in Limestone Creek, in Limestone County, Alabama. Populations seem very concentrated and only cover a very small area.

Historically, these two populations may have been part of one larger population. Piney Creek was once a tributary of Limestone Creek before the creation of the Wheeler Reservoir.

Threats

Due to small population sizes, limited occupied habitat, and annual life cycle, the armored snail is extremely vulnerable. Threats include direct loss of habitat, siltation, altered water chemistry and chemical pollution.

The placement of Wheeler Reservoir has greatly impacted this snail's habitat. Dams and their impounded water can form barriers to snail movement, promote siltation and encourage changes in the flow of water and water chemistry. This reduces food and oxygen availability, affecting reproductive success and altering habitat.

In addition, when local water and habitat quality change, many isolated snail populations become more vulnerable to run-off and discharges into the watershed.

Additional sources of siltation include channel modification, agriculture, cattle grazing, logging, chip mills, unpaved road drainage, rock quarries, bridges and road expansion projects and industrial and residential development.

Discharges from polluting sources increase eutrophication, decrease dissolved oxygen concentration, increase acidity and conductivity, and create other changes in water chemistry. Some sources include leach from agricultural fields (especially cotton), residential lawns, livestock operations and leaking septic tanks which also contribute to changes in water quality.

Conservation and Recovery

Current conservation measures include the certain designation of critical habitat and a review of all projects affecting habitat. After projects are reviewed appropriate conservation measures will be taken.

The U. S. Fish and Wildlife Service has determined that dams and their impoundments prevent the natural recolonization of surviving snail populations. Even if watershed impacts improve or even disappear, the damage will continue as long as the dams are present.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

Asheville Field Office
U. S. Fish and Wildlife Service
160 Zillicoa Street
Asheville, North Carolina 28801-1082
Telephone: (828) 258-3939
Fax: (828) 258-5330

References

United States Department of the Interior. 25 February 2000. "Endangered and Threatened Wildlife and Plants: Endangered Status for the Armored Snail and Slender Campeloma." Federal Register 65 (38).

Hershler, R. 2 January 1998. "A Systematic Review of the Hydrobiid Snails (Gastropoda: Rissooidea) of the Great Basin, Western United States. Part I. Genus Pyrgulopsis." The Veliger. 41 (1): 1-132.