> Habitat & Distribution
The range of H. magnifica appears to be restricted to the Cape Fear River drainage in the vicinity of Wilmington, NC. Early records were only from the lower Cape Fear River and from Greenfield Lake (Bartsch 1908, Baker 1945), both of which have been environmentally degraded in recent years. There was concern that H. magnifica was extinct until the 1986 and 1993 discoveries of populations in Orton and Sandhill Creek Ponds, respectively (Adams and Gerberich 1988, SCFTM 1990, Adams and Brady 1995). FWGNA incidence rank I-2.
> Ecology & Life History
Helisoma magnifica appears to be restricted to sheltered regions of lentic environments with diverse aquatic vegetation (SCFTM 1990). In Orton Pond, individual snails were typically collected from the stems and leaves of floating plants growing above a benthic substratum dominated by decomposing plant material (Adams and Gerberich 1988).
> Taxonomy & Systematics
The CO1 sequence data of Bogan et al. (2003) suggested that H. magnifica
is phylogenetically distinct from a variety of other planorbids
inhabiting the eastern United States, with a minimum sequence
divergence of 4.6% to the most similar taxon, H. trivolvis.
The classification of the Planorbidae proposed by the tag team of Baker (1945) and Hubendick (1955) remains, after 50 years, the basis for our understanding of this large and diverse family of pulmonates worldwide. Burch followed Taylor (1966) in promoting Baker's subgenus Planorbella to generic rank and moving magnifica into it, but we disagree, for reasons elaborated in my essay of 11Apr08, accessible below.
> Supplementary Resources [PDF]
- See my post to the FWGNA blog of 11Apr08 for a review of the Classification of the Planorbidae.
- Or view the (Hubendick 1955) classification of North American planorbids in a tabular format [here].
Adams, W.F., and A.G. Gerberich. 1988. Rediscovery of Planorbella magnifica Pilsbry in southeastern North Carolina USA. Nautilus 102:125-126.
Adams, W.F., and S.G. Brady. 1995. Rediscovery of the aquatic gastropod Helisoma eucosmium (Bartsch, 1908), (Basommatophora: Planorbidae). Brimleyana 22:23-29.
Baker, F.C. 1945. The Molluscan Family Planorbidae. The University of Illinois Press. Urbana, Illinois.
Bartsch, P. 1908. Notes on the fresh-water mollusk (Planorbis magnificus) and descriptions of two new forms of the same genus from the southern states. Proc. US Nat. Mus. 33: 697-700.
Bogan, A. E., M. R. Raley and J. F. Levine (2003) Final report on the taxonomic status of the Greenfield ramshorn, Helisoma eucosmium (Bartsch, 1908) and the magnificent ramshorn, Planorbella magnifica (Pilsbry 1903) (Mollusca, Gastropoda, Planorbidae) from eastern North Carolina. Unpublished report filed with the US Fish & Wildlife Service, Asheville. 22 pp.
Hubendick, B. (1955) Phylogeny in the Planorbidae. Trans. Zool. Soc. London 28: 453-542.
Scientific Council on Freshwater and Terrestrial Mollusks. 1990. (W. F. Adams, Chair) A report on the conservation status of North Carolina’s freshwater and terrestrial molluscan fauna.
Taylor, D. W. (1966) Summary of North American Blancan nonmarine mollusks. Malacologia 4: 1 - 172.