Editor's Note. This essay was subsequently published as: Dillon, R.T., Jr. (2019c) Goodbye Goniobasis, Farewell Elimia. Pp 19-22 in The Freshwater Gastropods of North America Volume 3, Essays on the Prosobranchs. FWGNA Press, Charleston.
The systematic relationships among Pleurocera, Goniobasis, Elimia, and several other nominal genera of slender pleurocerids in eastern North America first rose to our attention in February of 2007 (1). Faithful readers may remember the post to this blog entitled “Goodrichian Taxon Shift,” in which I reported a survey of gene frequencies in a pleurocerid population inhabiting Indian Creek, a small river in the remote southwestern corner of Virginia. The shell morphology demonstrated by that particular population varied from the slender and carinate “Goniobasis acutocarinata” form in the headwaters to the smooth and more heavily shelled Goniobasis clavaeformis form in the main creek itself. And at the mouth, where Indian Creek emptied into the Powell River, the shell morphology of this single population of pleurocerids became so chunky as to appear to change genera, to “Pleurocera unciale.”
I returned to this subject in October of 2009 under the title “Pleurocera Puzzles” (2). In that second post I reported an extension of my Indian Creek study to include pleurocerid populations inhabiting three additional subdrainages: the Pistol/Little River near Maryville (TN), the Conasauga/Hiwassee River east of Etowah (TN), and the Coahulla/Oostanaula River in North Georgia. In all four cases, the populations of Pleurocera inhabiting downstream reaches were more genetically similar to the local “Goniobasis” populations immediately upstream than to other nominal Pleurocera populations. This would seem to confirm that the shell attributes by which Pleurocera and Goniobasis have historically been distinguished cannot stand.
Taxonomic controversies have simmered within the tiny, closely knit scientific community working on the North American Pleuroceridae since the birth of American malacology. In my blog post of November 2010, I reviewed the longstanding disagreements over the generic nomina Pleurocera, Lithasia, and Oxytrema, which continued through most of the 20th century (3). More visible recently has been the controversy regarding the generic nomina Goniobasis and Elimia, which I reviewed in a blog post way back in September of 2004 (4).
We’ve been beating each other up over whether to call these populations Pleurocera, Oxytrema, Goniobasis, Elimia, and God Knows What Else for almost 200 years, and there’s never been a nickel’s worth of biological difference in the lot of them (5). Let’s put all this behind us, shall we?
The research results I telegraphed to this group in October 2009 have just been published in the issue of Malacologia currently on the newsstands. In Appendix 1 of that paper I formally synonymize Goniobasis, Elimia, and eight more obscure genera under the genus Pleurocera (Rafinesque, 1818). A pdf download is available from link (6) below. See pp 276 - 77.
The FWGNA site has been completely updated to correct all primary instances of the generic nomen “Goniobasis” to the most recent taxonomy (7). I would invite my colleagues to do likewise with the generic nomen, “Elimia.” Let the peace of Pleurocera begin.
(1) Goodrichian Taxon Shift [20Feb07].
(2) Mobile Basin III: Pleurocera Puzzles [12Oct09]
(3) Joe Morrison and the Great Pleurocera Controversy [10Nov10]
(4) Goniobasis and Elimia [28Sept04]
(5) DAZO, B.C. (1965) The morphology and natural history of Pleurocera acuta and Goniobasis livescens (Gastropoda: Cerithiacea: Pleuroceridae). Malacologia 3:1-80. STRONG, E.E. (2005) A morphological reanalysis of Pleurocera acuta Rafinesque, 1831, and Elimia livescens (Menke, 1830) (Gastropoda: Cerithioidea: Pleuroceridae). Nautilus 119:119-132.
(6) Dillon, R. T., Jr. (2011) Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque, 1818). Malacologia 53: 265-277. [PDF]
(7) I did not change the file names, only the html text. Even so, the process took several days, and I’m still not sure I've caught every instance. If you find any stray “Goniobasis” in the text of the FWGNA site, let me know.