J. P. E. Morrison was 72 years old in the summer of 1979, retired from the Smithsonian for about four years, but nevertheless a large and imposing figure (2). He launched into a rambling but passionate tirade about the meaning of the generic nomen “Pleurocera,” oscillating wildly from 19th century historical chronologies to egg mass morphologies, glowering at me and daring me to defy him. I don’t remember the details of my response, but I do remember beginning with, “Easy, big fella.”
Old Joe’s passion was, for me at the time, difficult to comprehend. But in subsequent years I have come to realize that we were witnessing a rehearsal of The Great Pleurocera Controversy, a conflict rooted deeply in the parent rock of American Malacology, passed to Morrison (and me!) through many generations of malacologists gone before. Our story begins in 1818, when the eccentric polymath Constantine S. Rafinesque (3) published the nomen “Pleurocera” as a genus to contain six species of freshwater prosobranch gastropods, none of which he described. Then in 1819 Rafinesque proposed “Oxytrema” as a genus to contain a second set of species including what we have some reason to think may have been what is known today as Pleurocera canaliculata [Photo at right].
Joe Morrison strongly felt that the actual text of Rafinesque’s 1818 description (4) most closely fit the chunky, bumpy shell morphology of what is known today as Lithasia verrucosa [Photo below]. But by common use through the 19th century and into the 20th, the generic nomen “Pleurocera” became attached to (or perhaps transferred to?) snails bearing smooth, skinny shells like what is known today as Pleurocera canaliculata, or (biologically equivalent, see Note 5) Pleurocera acuta. And the chunky-bumpies became Lithasia, and the nomen “Oxytrema” fell into disuse. And the family name that ultimately prevailed for the entire group of freshwater snails was based on the smooth-skinny concept of the genus, “Pleuroceridae.”
Despite the ancient origins of this confusion, however, the Great Pleurocera Controversy was very much a phenomenon of the 20th century. It sparked in 1912, when Harold Hannibal designated the chunky-bumpy verrucosa as type of the genus Pleurocera, and burst into flame in 1917, when Henry Pilsbry agreed with Hannibal, and Bryant Walker  rose to defend the cause of the smooth-skinnies (6). Pilsbry appealed to the International Commission on Zoological Nomenclature for a ruling in 1925.
The case simmered in court for 55 years (7), during which time Calvin Goodrich pretty much monographed the entire North American Pleuroceridae in bits and pieces, using the nomen Pleurocera in its smooth-skinny sense, essentially deciding the issue (8). Along the way, comments supporting the smooth-skinny concept of Pleurocera were filed by Joshua Bailey, Emilio Berio, Arthur Clarke, Joe Rosewater, Henry van der Schalie, Billy Isom, and George Davis. Comments supporting the chunky-bumpy concept were filed by Dave Stansbery, Carol Stein, and Joe Morrison.
The historical minutiae around which the case ultimately revolved were complex. Toward the end of the controversy, some of the arguments made by Morrison and his allies were so arcane that one commissioner complained that they looked “suspiciously like sabotage.” But Morrison was not to prevail. On 4Nov1981 the ICZN handed down Opinion 1195, ruling in favor of the smooth-skinny concept of Pleurocera by a vote of 19-3 (9).
So was it simply a question of taxonomic priority between two Rafinesque names of 1818 and 1819 that brought Old Joe to his feet on that August morning in 1979, red-faced with rage? Rafinesque had been in his grave for 139 years, and does not seem to have cared which of his names was used during his own lifetime, in any case. And I had not even mentioned the genus Pleurocera during my entire 15 minute presentation – my paper was about Goniobasis only.
No. To fully appreciate the issues at stake in The Great Pleurocera Controversy, we must roll the clock back once again to 1954, and the publication of what may have been Joe Morrison’s most important contribution to science, “The Relationships of Old and New World Melanians” (10).
Morrison’s (1954) work can only be appreciated through 19th century goggles. His introduction began with a statement of his hypothesis as an unquestionable fact, and a dismissal of any other hypothesis as “biological absurdity.” Morrison asserted that there are three freshwater cerithiacean families, each of which has evolved separately from marine ancestors: the Pleuroceridae from the Cerithidae, the Thiaridae from the Planaxidae, and the Melanopsidae from the Modulidae. He then reviewed the entire worldwide fauna of freshwater cerithiacean snails in 28 pages of text, focusing first on their taxonomy, and second on their reproductive biology, especially egg laying habit. He concluded his paper with a single plate of original observations, almost entirely external right-side sketches of extended females, showing egg laying grooves or brood pouches.
This was a tremendously ambitious work – the first worldwide review of the freshwater cerithiacean gastropods. By the standards of such contemporaries as Bengt Hubendick (11), it was embarrassingly slapdash. But in comparison with the much older, regional monographs it sought to review and synthesize, such as that of Tryon 1873, it was an improvement.
And to my eyes, the most significant innovation that Morrison introduced to the classification of the freshwater cerithiacean fauna worldwide in 1954 was his concept of a genus that he called “Oxytrema.” Morrison advocated combining all the sexually reproducing freshwater cerithiaceans bearing tall skinny shells … not just the species that Walker & Goodrich assigned to Pleurocera but also those they called Goniobasis (and Juga from the American West, and even many East Asian species) into this single gigantic genus on the basis of female reproductive habit. He wrote:
“Oxytrema Rafinesque is the earliest and correct name for one of the most widespread "Melanian" genera in the world. This genus includes numerous North American species whose ranges extend from the Atlantic to the Pacific coasts and from southern Canada to Florida and Texas. It also includes North American fossils, as well as a number of Recent species from southeast Asia (Korea, China, and Thailand). All the species called "Pleurocera" by Bryant Walker, and other authors who followed him blindly, and the species called "Goniobasis" (with very few exceptions) belong to this genus. Their eggs are laid in a single row in a close, irregularly spiral group, in apparent flat clusters of 3 to 10 egg capsules in each small egg mass, the whole covered with sand grains."So now we understand, at long last, how a 24-year old graduate student could incur the Wrath of Joe on an August morning in 1979 simply by referring to a genus named “Goniobasis.” Morrison needed the 1819 Rafinesque nomen Oxytrema to legitimize a massive, worldwide taxonomic revision, pushing Goniobasis underneath it, even as he needed to save the name Pleurocera by pushing it aside for another use.
Old Joe died in 1983. I remain, to this day, unable to assess the validity of his taxonomic arguments, but in the wake of the 1981 decision of the ICZN, they have become moot (12). Portions of his biological argument, however, seem to have considerable merit on the basis of much more than eggs. A paper supporting the combination of Pleurocera (as we know it today) and Goniobasis had already been published in 1965 by B. C. Dazo, hailing from Ann Arbor (of all places), the home of Walker and Goodrich. And Dazo’s results have more recently been confirmed and expanded by Ellen Strong (13).
And faithful readers of this blog may remember my posts of 20Feb07 and 12Oct09, demonstrating that shell morphology within a single population of pleurocerids can range from Goniobasis-like to Pleurocera-like as a correlate of stream size, probably a consequence of ecophenotypic variation (14). Might a measure of posthumous vindication for Old Joe Morrison yet be in store?
(1) Subsequently published as: Dillon, R. T., Jr & G. M. Davis (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia 20: 83-98. [pdf]
(2) The photo of Morrison above was downloaded from what amounts to his obituary, although it was not advertised as such: Rosewater, J. (1984) A bibliography and list of taxa of Mollusca introduced by Joseph P. E. Morrison Dec 17, 1906 – Dec. 2, 1983. The Nautilus 98: 1-9.
(3) The life of C. S. Rafinesque (1783 - 1840) is the stuff of legend. Google his name and see what I mean. An (1864) work by W. G. Binney and G. W. Tryon entitled, "The Complete Writings of Constantine Smaltz Rafinesque on Recent & Fossil Conchology" is available from the Biodiversity Heritage Library website, if you're hungry for more.
(4) From Binney & Tryon: "Univalve. Shell variable oboval or conical, mouth diagonal crooked, rhomboidal, obtuse and nearly reflexed at the base, acute above the connection, lip and columella flexuose entire. Animal, with an operculum membranaceous, head separated from the mantle inserted above it, elongated, one tentaculum on each side at its base, subulate acute, eyes lateral exterior at the base of the tentacula."
(5) Although populations of the snails identified as Pleurocera acuta today [photo right] are biologically quite similar to populations of the snails we currently identify as P. canaliculata, the specific nomen “acuta” became almost as entangled taxonomically as the generic nomen “Pleurocera.” Ultimately “Pleurocerus acutus” was chosen as the type of the genus. See Opinion 1195 (Note 9) for the gory details.
(6) Pilsbry, H. A. (1917) Rafinesque's genera of freshwater snails. Nautilus 30: 109-114. Walker, B. (1917) The type of Pleurocera Rafinesque. Occas. Pprs. Mus. Zool. Univ. Mich. 38: 1 - 10.
(7) Secretary R. V. Melville offered a detailed apology for the extraordinary delays suffered in the resolution of the Pleurocera question in Opinion 1195 (Note 9).
(8) For more see my previous blog post: The Legacy of Calvin Goodrich [23Jan07]
(9) Melville, R. V. (1981) Opinion 1195. Pleurocera Rafinesque, 1818 (Gastropoda): The type species is Pleurocerus acutus Rafinesque in Blainville, 1824. Bulletin of Zoological Nomenclature 38: 259-265.
(10) Morrison, J. P. E. (1954) The relationships of Old and New World Melanians. Proc. U. S. Nat. Mus. 103: 357- 394.
(11) For more about Bengt Hubendick, see my previous blog posts: The Classification of the Lymnaeidae [28Dec06] The Classification of the Planorbidae [11Apr08]
(12) But it is not a stretch to view the ongoing Goniobasis/Elimia taxonomic controversy as a consequence of the Pleurocera controversy that preceded it. J. B. Burch rationalized his decision not to apply to the ICZN for conservation of the more familiar Walker & Goodrich nomen Goniobasis over the Pilsbry Elimia by referring to the "inordinate amount of time" required to reach an opinion on Pleurocera. For more see my post on Goniobasis and Elimia [28Sept04].
(13) 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.
(14) See my previous blog posts: Goodrichian Taxon Shift [20Feb07] Mobile Basin III: Pleurocera Puzzles [12Oct09]
 Note added subsequently. In my post of [9Nov12] I elaborate at some length on Bryant Walker's Sense of Fairness.