Rediscovery of the Aquatic Gastropod 



Helisoma eucosmium (Bartsch, 1908), 



(Basommatophora: Planorbidae) 



William F. Adams 



Environmental Resources Branch 



United States Army Corps of Engineers 



P.O. Box 1890, Wilmington, North Carolina 28402 



AND 



Susan G. Brady 



Department of Biology 



University of North Carolina at Wilmington 



601 South College Road, Wilmington, North Carolina 28403 



ABSTRACT — A population of Helisoma eucosmium (Bartsch, 1908), 

 a small freshwater planorbid snail considered to be extinct by 

 some authors, has been discovered in Town Creek, a tidal 

 swamp stream in southeastern North Carolina. This rediscovery 

 will permit a definitive determination of the proper systematic 

 placement of the taxon. In the absence of live specimens, past 

 analysis of this taxon during systematic revisions of the Planorbidae 

 relied only on shell morphology of type material. Under this 

 circumstance, this taxon was variously placed in both tropical 

 and temperate genera and, compounding that problem, was treated 

 as a full species by some authors and a subspecies by others. 

 Its apparently limited range elevates concern for the conserva- 

 tion of planorbid snail diversity in southeastern North Carolina 

 because it is the second taxon with a severely restricted dis- 

 tribution to be found in this rapidly urbanizing region. 



Helisoma eucosmium (Bartsch, 1908) is a small, distinctive planorbid 

 snail which was collected and described from Greenfield Lake, a 

 millpond constructed prior to 1750 (Adams 1990a). This site is located 

 within the City of Wilmington, New Hanover County, North Carolina, 

 and is on a tributary to the lower Cape Fear River. During the past 

 few decades, repeated attempts to recollect H. eucosmium in Greenfield 

 Lake and elsewhere within the region have been unsuccessful (Fuller 

 1977, Adams 1990a). This fact, combined with the water quality degradation 

 in many regional streams, has led many investigators to treat the 

 taxon as extinct (Opler 1976, Imlay 1977, Palmer 1985) or possibly 

 extinct (Fuller 1977, Adams 19906). 



Brimleyana 22:23-29, June 1995 23 



