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Spiny Riversnail

Io fluvialis
Many species of mollusks, like the
Spiny Riversnail (Io fluvialis)
are either extinct or missing from state waters.
The Alabama Aquatic Biodiversity Center (AABC)
will lead efforts to return many species to state waters,
where future generations of Alabamians
will benefit from the clean water initiatives
these unique animals can promote.

Common Name: Spiny Rocksnail
Scientific Name: Io fluvialis
Other Names: none

Size: 50 mm [2 in.]

Description: Highly variable with regard to shell morphology.  Spiny form typically found in large rivers and occurred in Alabama historically.  Shell thick (max. length = approx. 50 mm [2 in.]), fusiform in outline, with a tapered, elevated spire.  Whorls somewhat convex to inflated and sutures not impressed.  Body whorl sculptured by wrinkled growth lines and marked by series of spines in middle of whorl.  Spines vary from raised knobs to large spines that are of equal height and width.  Aperture elliptical and about one-half length of shell, with a well-developed basal channel.  Inside of aperture whitish and often marked with dull reddish lines.  Periostracum olive green to brown.  Columella concave in imperforate.  (Modified from Tryon 1874, Bogan and Parmalee 1983)

Distribution: Endemic to Tennessee River system.  Downstream limit reportedly Muscle Shoals (Adams 1915), but not reported from Alabama since Tennessee River impounded.  Recently reintroduced into tailwaters of Nickajack Dam, Marion County, Tennessee (P. D. Johnson, Southeastern Aquatic Research Institute, pers. comm., 2002).  If reintroduction successful, should result in recolonization of upper reaches of Guntersville Reservoir.

Habitat: Large rocks and bedrock outcrops in well-oxygenated, shallow water with fast current (Bogan and Parmalee 1983)...

Life History and Ecology: Reported to lay two to six clutches of eggs during late April and May, with clutches containing 16 to 100 eggs each.  Laid without a sand-grain covering in a diagonal pattern with rows of one to five eggs that begin to hatch after about 15 days (Bogan and Parmalee 1983).

Basis for Status Classification: Extirpated from Alabama with impoundment of Tennessee River.  However, if planned reintroductions into Nickajack Dam tailwaters are successful, should expand distribution downstream into Alabama.  Listed as endangered in Alabama (Stein 1976).

above from Alabama Wildlife, Volume 2 (2004), prepared by: Paul D. Johnson 


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