Dr. Rob Dillon, Coordinator

Tuesday, May 9, 2023

Testing the Periwinkle Hypothesis

Editor’s Note – This essay is the second half of a two part series on the systematics of the pleurocerid genus Leptoxis.  We recommend that you familiarize yourself with last month’s post [6Apr23] before proceeding.

I first met Nathan Whelan, that brash young star of find ‘em and grind ‘em malacology, at the Louisville meeting of the FMCS in April of 2011 [1].  He was bubbling with excitement about his dissertation research at the University of Alabama, “the first phylogenetic study of Leptoxis to have complete ingroup and adequate outgroup sampling.”  Nathan’s 157-page dissertation, which included chapters on egg laying behavior and nuclear copies of mitochondrial genes (NUMTs), in addition to an extraordinarily ambitious molecular phylogeny, was published in 2013 [2].

Nathan analyzed N = 207 individual snails, focusing on 154 Leptoxis sampled from 39 populations of 13 nominal species, to which he added a very large number of outgroups: 23 Pleurocera/Elimia, 20 Lithasia, 4 Juga, an Io sample fished from Genbank, 2 Cleopatra from Zambia, and 3 “undescribed pleurocerids” from the Collins River for which he would not hazard even a genus.

He sequenced two nuclear genes (Histone H3 and 28S rRNA) and two mitochondrial genes (16sRNA and CO1) for his big sample, and immediately discovered 28 cases of mitochondrial superheterogeneity, recalling the phenomenon my coworkers and I reported in 2009 [3].  These highly divergent sequences he attributed to NUMTs, an hypothesis which his subsequent research did not confirm [4].  Soldiering on undaunted, he excluded 23 individual Leptoxis and 5 individual Lithasia from further analysis, paring his total sample size down to N = 179.

Whelan [1] Fig 5.4, diagrammatic

The figure above is a diagrammatic representation of Nathan’s Figure 5.4, a Baysian tree based on concatenation of the four genes, simplifying 179 branch tips [5] down to eight boxes.  I would suggest that you right-click on that figure and open a larger version in a new window, because we're going to discuss it in some detail.  And if you’d like to see Nathan's original tree, with all 179 tips unfolded and labelled, you are hereby invited to open [this link] in a third window as well [6].  And you'll need to max that third window up to life size.  Nathan’s original Figure 5.4 was printed in 7-point font over two sequential 8.5 x 11 inch print pages, which I have pasted together into a single 15 x 20 inch jpeg image for detailed examination.  OK, are we ready to go forward?

The box shown in dashed outline at the bottom of the diagrammatic representation symbolizes 26% of the foliage of the tree, a total of 47 sequences, including all the Pleurocera/Elimia, all the Lithasia, the Io and the unidentified. Mingled in amongst the branches bearing all those taxa are the sequences from three species of Leptoxis: L. compacta (5), L. plicata (2) and L. arkansensis (4).  This is the phenomenon for which Nathan subsequently [7] coined the term, “prodigious polyphyly” implying that results such as these bear some relationship to the evolutionary relationships among the pleurocerid populations from which they were drawn.

But gene trees are dependent variables, not independent variables. Although they might certainly cast light on an hypothesis, they cannot be used to construct an hypothesis.  And since I personally do not have enough research experience with Leptoxis compacta, L. plicata, or L. arkansensis to have formed an hypothesis regarding their evolutionary relationships [8], let’s trim the lower quarter of Nathan’s tree off, and set those data aside.  One day we may be able to interpret them.  But today is not that day.

Now moving forward with the 74% of Nathan’s tree for which, over 50 years of experience, I have developed an expectation. From top to bottom, six results present themselves for discussion.

First, Nathan’s results support the 1998 hypothesis of Dillon & Lydeard [9] that the Leptoxis of the Alabama/Coosa system are conspecific, Leptoxis picta (Conrad 1834) being the oldest available name.  The nomina ampla (Anthony 1855), foremani (Lea 1843), and taeniata (Conrad 1834), are all junior synonyms of picta.

Second, Nathan’s results support the hypothesis of Dillon & Robinson [3] that populations previously identified as Leptoxis dilatata in the New/Greenbrier/Kanawha are trans-Appalachian Leptoxis carinata.

Leptoxis carinata eggs

And third, Nathan’s results support the hypothesis of Dillon & Ahlstedt [10] that Leptoxis crassa is closely related to, but specifically distinct from, Leptoxis praerosa.  Reproductive isolation seems to have arisen in an East Tennessee population of L. praerosa, rather than in Middle Tennessee, North Alabama, or elsewhere [11].  The subsequent level of divergence does not seem to be of the magnitude of a subgenus, much less a genus.  The longstanding hypothesis that large-bodied, heavily shelled pleurocerid populations described as Melania crassa (Haldeman) or Melania anthonyi (Redfield) might be set aside in a unique genus “Eurycaelon” or Athearnia” is not supported.

Fourth.  Nathan’s gene tree depicts 8 populations of Leptoxis praerosa sampled from East Tennessee (four Clinch, one Powell, two Holston, one Nolichucky, comprising 14 individuals in total) as distinct from 9 populations (22 individuals) sampled from elsewhere throughout the remainder of the range.  Nathan suggested that this phenomenon might reflect speciation, going so far as to nominate subglobosa (Say 1825) as a possible name for the East Tennessee populations.

There is no evidence of sympatry between the eight L. praerosa populations in Block 4 and the other nine populations in Block 5, however.  Such a phenomenon is just as easily explained by geographic isolation as by reproductive isolation.  Walden Ridge, constituting the eastern escarpment of the Cumberland Plateau as it slashes diagonally through Tennessee to Chattanooga, has long been recognized as an important biogeographic boundary separating the aquatic faunas of East and Middle Tennessee, and cannot be ruled out as a causative agent for the genetic discontinuity apparent between Block 4 and Block 5 above.

Fifth.  Subsumed among the nine populations in the main Leptoxis praerosa Block 5 were two populations Nathan identified as Leptoxis umbilicata – one from the East Fork Stones River (5 individuals) and a second from Smith Fork of the Caney/Collins (3 individuals).  There is no evidence of any genetic divergence between these two populations and Leptoxis praerosa sampled more broadly.

Indeed, our field surveys conducted throughout the Tennessee/Cumberland catchment have confirmed populations of otherwise typical L. praerosa bearing openly-umbilicate shells in the Stones River subdrainage as well as in the Red River subdrainage (NW of Nashville) and (sporadically) in the Elk.  Intrapopulation variation such as that depicted from a tributary of the Red River below, together with the genetic data of Whelan, suggest that L. umbilicata (Wetherby 1876) be lowered to subspecific status [12] under Leptoxis praerosa.

Leptoxis praerosa umbilicata

And sixth, and most interestingly.  Nathan identified a set of 7 populations (21 individuals) from all around East Tennessee and North Alabama, in the Holston, Hiwassee, Nolichucky, Sequatchie, Paint Rock and elsewhere, as “Leptoxis virgata.”  That subset of 7 populations seems to bear a distinct mitochondrial haplotype, differing by roughly 0.8 mystery units of divergence [13] from his 8 + 9 = 17 populations of L. praerosa.  These 7 “virgata” populations seem effectively sympatric with praerosa populations over their entire range, collectable side-by-side in the Nolichucky River at the SR340 bridge, Greene County, TN.

The molecular distinction between L. praerosa and “L. virgata” seems to be entirely mitochondrial.  Although Nathan included nuclear 28S and H3 data in his concatenated Fig 5.4 tree, the separate trees he figured for the two nuclear genes individually did not seem to resolve L. "virgata" from the greater Leptoxis background.  The praerosa/”virgata” distinction does, however, seem to include a morphological component.  Nathan stated that “the shells of these species are slightly different” but did not elaborate.  You can be the judge from his Figure 4.5 below.

Nathan’s mitochondrial data plus the demonstrated sympatry plus the (putative) shell morphological differences all combine to suggest that a pair of cryptic Leptoxis species co-occur in the rivers of East Tennessee.  And since the range of the more widespread (17-population) species extends north and west to include the Falls of The Ohio, the best identification for the 17-population species must be Leptoxis praerosa.  Nathan’s identification of the 7-population species as “Leptoxis virgata” is, however, premature.

Before signing off on his dissertation, Nathan’s advisor should have sent him back to the Nolichucky River at the SR340 bridge to do the job right.  Nathan should have been instructed to collect a big, fresh sample of Leptoxis, paying close attention to microhabitat, photograph them all, and measure their shells thoroughly.  Then he should have sequenced them, and sorted them into two piles according to mtDNA haplotype.  And then he should have cracked open a can of geometric morphometrics, or maybe an old-fashioned cigar box of discriminant function analysis, or maybe an even older-fashioned bivariate statistical analysis, to see if any difference in the morphology of those two piles of Leptoxis shells could be confirmed.

Whelan [1] Fig 4.5, modified

In the Pleuroceridae, species are defined by shell morphology.  So if Nathan had indeed been able to detect some shell morphological difference correlated with the mtDNA sequence divergence at the SR340 bridge, he should then have gone back into the national collections and conducted a similar morphological analysis on all the type specimens of all the Leptoxis available, or (in any case) their images as reproduced in their descriptions, and tried to find a match.

If, however, no shell morphological difference manifests itself at the SR340 bridge, the pair of species may be judged true siblings.  Then again, Leptoxis praerosa is (by definition) the name for the more widespread.  For the less-widespread, perhaps the best course of action, only at this point, would have been to find a good-fitting junior synonym of L. praerosa to resurrect.  Perhaps virgata (Lea 1841) is that synonym [14].  My nominee would be subglobosa (Say 1825).  But in no case and at no time in this entire process are any additional newly-described pleurocerid nomina wanted on the floor of the Augean Stables [15].  I think Nathan and I are together on that.

Alas, none of the above happened in 2013.  If I were 20 years younger, the study as I have outlined it would have taken place in 2014 – 2015, using allozyme markers, which are much more powerful than sequence data, but alas again, I am not.  So, if any of you bright young students out there are shopping for a research project, I’ve got a great one all laid out for you on the banks of the Nolichucky.  In fact, I’ve already got the manuscript written for you, like a malacological ChatGPT.

Go back and re-read the series of three essays I posted in the fall of 2016 on the cryptic Pleurocera of Maryville [16].  You have my permission to copy and paste all that text into a fresh manuscript, substitute Leptoxis for Pleurocera and Nolichucky River for Pistol Creek, submit to Science or Nature, and call a press conference.  Your next big NSF grant is assured, your tenured professorship awaits.


[1] In the original version of this essay, posted Tuesday afternoon 9May23, I stated that I first met Nathan in July of 2011 at the AMS.  Nathan corrected me in an extensive comment posted shortly thereafter.  His original 9May comment was subsequently deleted by Google, however, possibly because of some of the inflamatory language it included.  So I resurrected his comment from the blogspot archives, emailed it back to Nathan, and he cleaned it up, and re-posted it on 11May.  Look way down below.

[2] Whelan, Nathan V. (2013)  Conservation, life history and systematics of Leptoxis Rafinesque 1819 (Gastropoda: Cerithioidea: Pleuroceridae).  PhD Dissertation, University of Alabama, Tuscaloosa.  179 pp.

[3]  Dillon, R T. and J. D. Robinson (2009)  The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?  Journal of the North American Benthological Society 28: 1 - 11. [pdf]  To review the state of our knowledge at that (relatively early) stage in our understanding of the phenomenon we subsequently termed “mitochondrial superheterogeneity,” see:

  • The snails the dinosaurs saw [16Mar09]

[4] Whelan, N.V. & E. E. Strong (2016)  Morphology, molecules and taxonomy: extreme incongruence in pleurocerids (Gastropoda, Cerithiodea, Pleuroceridae). Zoologica Scripta 45: 62 – 87.  To review the state of our understanding of mitochondrial superheterogeneity at this (much improved) state see:

  • Mitochondrial superheterogeneity: What we know [15Mar16]
  • Mitochondrial superheterogeneity: What if means [6Apr16]
  • Mitochondrial superheterogeneity and speciation [3May16]

[5] There is some discrepancy between the number of branch tips depicted in Nathan’s Figure 5.4 and the number of samples as listed in his Table 5.2, possibly due to duplicate sequences.  The sample sizes shown in my diagrammatic representation come from the Table, not the Figure.

[6] Here is Nathan Whelan’s (2013) Figure 5.4:

  • Baysian phylogram inferred with the concatenated dataset with Cleopatra dropped for visualization purposes. [jpg]  Numbers in front of nodes are posterior probabilities for each node.  Scale bar meaningless.

[7] Whelan, N. V., P.D. Johnson, J.T. Garner, N.L. Garrison, & E.E. Strong (2022) Prodigious polyphyly in Pleuroceridae (Gastropoda: Cerithioidea).  Bulletin of the SSB 1(2): 8419.

[8] I do have an hypothesis or two about the origin of “prodigious paraphyly,” however.  Nathan’s Table 5.2, providing the sampling details for the 207 individual snails sequenced for his study, lists 63 populations, 31 of which had sample sizes of 1 – 2 and 32 had sample sizes 3 – 6.  Of the latter 32, 13 demonstrated superheterogeneity ranging from 1 – 3.  Given such a background sampling distribution, it seems likely to me that at least one or two populations of N = 5 (e.g., L. compacta) might be 100% superheterogeneous, pushing L. compacta (for example) entirely off the Leptoxis branches of Nathan’s tree.

[9] Dillon, R.T., and C. Lydeard (1998) Divergence among Mobile Basin populations of the pleurocerid snail genus, Leptoxis, estimated by allozyme electrophoresis.  Malacologia. 39: 111-119. [pdf]

[10] Dillon, R. T., and S. A. Ahlstedt (1997) Verification of the specific status of the endangered Anthony's River Snail, Athearnia anthonyi, using allozyme electrophoresis. The Nautilus 110: 97 - 101. [pdf]

[11] The speciation of Leptoxis crassa from a Leptoxis praerosa population rendered L. praerosa paraphyletic.  A cladist is any biologist who, upon first hearing the definition of the word, “paraphyly,” didn’t immediately react, “So, what?”

[12] Subspecies are populations of the same species in different geographic locations, with one or more distinguishing traits.  For more, see:

  • What is a subspecies? [4Feb14]
  • What subspecies are not [5Mar14]

[13] As fastidious as he is about the nodes of his gene trees, Nathan is cavalier with the branches.  His Chapter 5 phylogenetic studies include no data on percent sequence divergence whatsoever.  And (alas) I could not find any of his 2013 sequence data in GenBank.  But the scale bar at the bottom of his Figure 5.4 is marked “0.4,” so eyeballing from that, it appears that the sequence divergence between his L. virgata cluster and his larger L. praerosa cluster is approximately 0.8 somethings.

[14] Isaac Lea described Melania virgata in 1841 from a single 0.3 inch (=7.6 mm) shell sent to him by Dr. Troost from “Tennessee.”  Tryon demoted virgata to a “variety” of Anculosa subglobosa.  But Lea’s little figure of the shell, showing a relatively small aperture (“about half the length of the shell”) seems to depict a youngish Leptoxis carinata, a population of which has indeed jumped over the low hills from the New River into the Holston of Virginia, and could indeed have been picked up by Troost downstream in Tennessee.  So Goodrich shifted virgata over to the genus Nitocris with carinata as he synonymized Anculosa subglobosa under A. praerosa.  Burch followed Goodrich biologically, although not taxonomically, substituting Leptoxis for Anculosa, grouping virgata with carinata in the subgenus Mudalia, leaving praerosa in the typical subgenus.  Bottom line is that in choosing to identify a putative species cryptic under praerosa as “Leptoxis virgata,” Nathan is following Tryon, and disagreeing with Goodrich, Burch, and Rob Dillon, all three of us together.  Brash.

[15] This is an oblique reference to a very specialized, and hence very useful, reference work to the taxonomy of the Pleuroceridae:

  • Graf, D. L. (2001)  The cleansing of the Augean stables.  Walkerana 12(27): 1 - 124.

[16] My three-part series on the rediscovery of Pleurocera gabbiana, cryptic under P. simplex in East Tennessee, was published both informally on this blog and more formally, in the FMCS Newsletter.  See:

  • [13Sept16] Dillon, R. T. (2016) Two reproductively isolated populations cryptic under Pleurocera simplex (Say, 1825) inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 15-16. [pdf] 
  • [14Oct16] Dillon, R. T. & J. D. Robinson (2016) The identity of the "fat simplex" population inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 16-18. [pdf]
  • [14Nov16] Dillon, R. T. (2016)  Match of Pleurocera gabbiana (Lea, 1862) to populations cryptic under P. simplex (Say, 1825).  Ellipsaria 18(3): 10 - 12.  [pdf]

Thursday, April 6, 2023

Growing up with periwinkles

Back in 2014 I posted a reminiscence on this blog [1] about growing up a frustrated young malacologist in the little city of Waynesboro, Virginia.  From my house it was just a couple hundred yards through old fields to the South River, a tributary of the Shenandoah.  And I wrote:

“The rocks were (and still are) covered with little black snails we called ‘periwinkles.’ I didn't collect them for the same reason I didn't collect ants.  They were dirt-common, and (in retrospect) I think my collecting button only got pushed when I saw something that seemed unusual, which periwinkles were not.  And I knew for a fact that, just as was the case with ants, I could not identify those periwinkles, even if I dug through every "Mollusca" card in the University of Virginia Library catalog, which I had.”

I dropped the subject of “periwinkles” at that point of the essay, in favor of another even more common and even more frustrating freshwater snail, that of dirt-brown hue, Physa.  So, this month we’ll pick at that little-black periwinkle thread again and see what unravels behind it.

Because those periwinkles were the most conspicuous gastropod of my youth.  Further south up the Great Valley of Virginia my father and I spent many lovely hours fishing in the James River and tributaries such as the Cowpasture and the Jackson.  And the next river heading south was the Roanoke, where I had dozens of cousins, and the next river was the New River, in whose bosom I wiled away four sweet, gauzy years of college.  And in all of those river systems, in every rapid or riffle big enough for a sun perch or a redeye bass, the rocks were covered with little black periwinkles.

Jackson R, Va.

It was only after my arrival at Virginia Tech in the fall of 1973 that I was finally able to identify “periwinkles,” poking through the malacological journals, reading backward through the literature, discovering the work of Calvin Goodrich [2]Nitocris carinata!  Authored by the French zoologist Jean Guillaume Bruguière in 1792, “Bulimus” carinatus was the second freshwater gastropod [3] described from the continent of North America, “les eaux douces de la Virginie[4].  Goodrich gave its range as “New York to North Carolina.”

But almost immediately after I had solved the mystery of the specific identity of the periwinkle, a fresh mystery presented itself.  To what genus should the periwinkle be assigned?  Although Goodrich advocated Nitocris (H. & A. Adams 1854), Dr. E. F. (Fred) Benfield, my undergraduate advisor, preferred old Joe Morrison’s [5] Mudalia (Haldeman 1840).  Tryon [6] and Walker [7] preferred Anculosa (Say 1821).  And Juan Parodiz, who had authored the best review of the systematics and distribution of periwinkles to that date [8], made a case for Leptoxis (Rafinesque 1819), pushing Mudalia underneath Leptoxis as a subgenus.  It turned out that I had stumbled into one of the most contentious issues in American malacology.

There were actually two layers of controversy. The first was whether Rafinesque had described his (1819) Leptoxis with sufficient clarity that it might take precedence over Say’s (1821) Anculosa.  And the second was whether either of two subsequent names, Mudalia of Haldeman or Nitocris of H & A Adams, both originally proposed as subgenera, might deserve elevation to the full genus level.  Iced over those layers of controversy was the situation with a larger-bodied group that Tryon, Walker and Goodrich all referred to as Eurycaelon (Lea, 1864), but which Joe Morrison insisted was in error, for which he proposed the new name Athearnia in 1971, more below.  And then there was a funny little sprinkle of walnuts on top about Alleghenya.

Who among my vast and diverse readership has ever heard of Dr. Kenneth J. Boss?  I didn’t think so.  Boss was a student of Bill Clench, and heir to the curatorship of malacology at the MCZ Harvard.  He had a quiet career, bless his heart.  But in 1967 he and his mentor published a little paper ignoring Leptoxis, discounting Mudalia and Nitocris, and proposing to classify periwinkles in a new subgenus of Anculosa they called “Alleghenya[9].

L. carinata from Parodiz [8]
I met Ken Boss in January of 1977, when I was interviewing prospective graduate advisors.  And I asked him what the hell he was thinking with this Alleghenya thing, which was a pretty cheeky way for a 21-year-old student to address a Harvard professor.  And he admitted his mistake and apologized [10].

I ultimately chose Mudalia as the genus under which to file the periwinkles I collected during the course of my undergraduate thesis research [11], because that’s the name my faculty advisor preferred.  But three years after I graduated, Jack Burch [12] brought the tablets down the mountain, and engraved upon them was Leptoxis at the genus level, with Mudalia a subgenus beneath it.  Burch didn’t offer any rationale, but neither did God [13].  And Leptoxis it has been, ever since.

But here’s a fresh puzzle, now that we’ve identified those periwinkles that covered the rocks in the South River of my youth as Leptoxis (aka Nitocris, aka Mudalia) carinata (Brug 1792).  When I left home for college, I drove south up the Great Valley through the James River drainage, which was chock full of L. carinata, and the Roanoke River drainage, which was chock full of L. carinata, and then up the long grade to the New River Plateau.  But for reasons unknown and unexplained, Calvin Goodrich [14] identified the periwinkles of the New River drainage as Nitocris (aka Leptoxis, aka Mudalia) dilatatus (Conrad 1834), not carinata.

True, the vast herds of periwinkles covering the rocks in the New River tributaries outside my dorm room window in Blacksburg bore shells lacking that carination so often prominent on the shells borne by the herds of periwinkles outside my bedroom window in Waynesboro.  But by the time I was 20 years old I had been kicking those little things off rocks for 15 years, all over the Commonwealth of Virginia, and I knew how variable that little black shell could be.

And true, the New River drains west to the Ohio, while the Shenandoah, James, and Roanoke drain east to the Atlantic.  But even in my tender youth I was already tremendously impressed by the extensive geographic ranges demonstrated by pleurocerid snails.  I didn’t understand it.  Still don’t [15].  But as Goodrich observed, Leptoxis carinata is found in every Atlantic drainage from the Susquehanna way up in New York to the Broad/Congaree way down in North Carolina, and on that scale the 10 mile climb up I-81 leaving the Roanoke River Valley and entering the New River plateau seems insignificant.  And ditto continuing back down the Blue Ridge on I-77 south from the New to the Yadkin/Pee Dee.  The little black periwinkles swap carinata-dilatata-carinata over that 50 mile stretch, really?

"Mudalia dilatata" from my ugrad thesis [11]
Moreover, by my undergraduate years I was already becoming obsessed with another local pleurocerid, Pleurocera (aka Goniobasis, aka Elimia) proxima, the range of which did extend across the Dan/Roanoke through the New River into the Yadkin/Pee Dee, with no apparent interruption.  Why should Goodrich distinguish the New River Leptoxis with a unique name, “Nitocris dilatata”, while calling all the Pleurocera across the entire Roanoke-New-Pee Dee region “Goniobasis proxima?"

It took thirty years, but John Robinson and I ultimately answered that question in 2009, with the survey of CO1 sequence divergence we called “The Snails the Dinosaurs Saw [16]”  Although the focus of that study was mitochondrial superheterogeneity within populations, we did not neglect interpopulation divergence as well.  Our pair of carinata/dilatata populations from the Yadkin/New were more similar to each other than to their nominal conspecifics in a carinata/dilatata pair sampled from the James/Greenbrier 150 km north.  Conrad’s (1835) dilatata is a junior synonym of Bruguiere’s (1792) carinata.

But back to the thread of my story.  It was also during my undergraduate years at Virginia Tech that I was first introduced to the second-oldest species of Leptoxis in North America, Thomas Say’s “Melania” praerosa, described from the Falls of the Ohio in 1821.  The introduction came in 1975, during the summer after my sophomore year, when I was blessed to be offered a temporary job with the Tennessee Valley Authority in Norris, and it was my new co-worker Steve Ahlstedt who did the honors.  Interestingly, Steve called those little snails “Anculosa subglobosa,” which was my first introduction to a specific controversy almost as idiosyncratic as the controversy over the genus.

Thomas Say described “Melania subglobosa” from the North Fork of the Holston River in 1825, and the species was considered distinct and valid by all authors through the 19th and most of the 20th century, including by Tryon [6] and Goodrich [14], both of whom assigned it to Anculosa. But in 1980 Jack Burch [12] synonymized subglobosa under Say’s praerosa without explanation [17] or even comment.  He simply wrote, in the caption of the figure printed on his page 157: “FIG. 480. L. subglobosa = L. praerosa.” And just like that, Anculosa subglobosa (Say 1825) was gone.

By whatever name, I found Leptoxis praerosa populations as widespread and dense in the rich headwaters of the Tennessee River to the west of the New River as L. carinata were in the Yadkin/PeeDee to the South and the Dan/Roanoke to the east.  Interestingly, carinata has apparently dispersed into the upper Holston/Tennessee with praerosa, and praerosa seems to have spread into Walker Creek of the New River with carinata, and in neither of these drainage systems is any hybridization in evidence, to my eye, in any case.

Leptoxis praerosa, thanks to Chris Lukhaup
The two species are easy to distinguish by the relative sizes of their body whorls, L. praerosa’s being so large as almost to obscure the apex entirely, smoothly rounded and entirely unsculptured, with no hint of carination.  They look like pebbles, with a bit more mobility, but less personality.  It is perhaps their unmitigated plainness that has spared them the metastasis of synonymy that has afflicted almost every other biological species of pleurocerid snail in North America.  All across their eight-state range, Goodrich listed only nine synonyms for praerosa and four for subglobosa, all of which are too obscure to mention.

Because populations are so widespread throughout the Ohio, Cumberland, and Tennessee drainages, and because (up until recently) their identity was uncontroversial, Leptoxis praerosa was an easy choice as a control for two allozyme studies I published in the 1990s, one of Leptoxis crassa [18] and a second of the Alabama taxa L. picta, L. ampla, L. plicata, and L. taeniata [19].  In that former study, Steve Ahlstedt and I confirmed reproductive isolation at four loci between sympatric populations of L. praerosa and L. crassa co-occurring in the Sequatchie River, about 10 miles west of Chattanooga.

Steve and I identified the population of big-bodied pleurocerids we sampled from the Sequatchie as “Athearnia anthonyi.”  That was the name Steve wrote on the label in the bag of snails he shipped to me on dry ice, which I transferred to my data sheets, anyway.  In 1971 old Joe Morrison proposed Athearnia as a genus to hold two nominal species of large-bodied pleurocerids that Tryon, Walker and Goodrich had all previously assigned to Eurycaelon (Lea 1864): Melania crassa Haldeman 1842 and Melania anthonyi Redfield 1854 [20].  Burch demoted Athearnia to subgeneric rank under Leptoxis in 1980, and lowered anthonyi to subspecific level under crassa.  But in 1994 the US Fish & Wildlife listed “Athearnia anthonyi” as an endangered species, declaring A. crassa extinct in the process [21], pretty much freezing the 1971 science forever [22].

Leptoxis crassa in Limestone Ck.

So shortly after Steve Ahlstedt and I published our paper on L. crassa, Chuck Lydeard sent me a big batch of Leptoxis from the Mobile Basin [18].  I opened the cooler to find eight populations of four nominal species: three of L. ampla from shoals of the Cahaba River, two of L. taeniata from tributaries of the Coosa, two of L. plicata from Locust Fork (of the Black Warrior) and one of L. picta from the main Alabama River.  I found the levels of allozyme divergence among six of the eight comparable to that demonstrated by a set of three L. praerosa control populations I collected from Tennessee drainages separated by similar distances.  Our results suggested that ampla, taeniata, and picta were all conspecific, Leptoxis picta (Conrad 1834) being the oldest name for the lot.  The average allozyme divergence demonstrated by the L. plicata populations of the Black Warrior system was consistent with their status as a distinct biological species.

So if you had asked me ten years ago, I would have listed six valid species of Leptoxis in North America: carinata, praerosa, crassa, picta, plicata, and maybe that weirdo way out in the Ozarks, Leptoxis arkansensis (Hinkley 1915), I have no reason to doubt.  That six-species hypothesis comes from over 60 years of field experience with Leptoxis in the creeks, thousands of hours of laboratory research on the genetics of pleurocerid populations, and an intimate familiarity with 200 years of accumulated scientific literature.  It is science.  It is a testable model of the natural world.  Next month, we test it.


[1] This was the first episode in what turned out to be a five-part series on the evolution of our understanding of the North American Physidae.  If you’re curious about the entire Physa story, the best approach might be to go to the final installment [6Dec18] and read backwards.  Otherwise:

  • To Identify a Physa, 1971 [8Apr14]

[2] Goodrich, C. (1942) The Pleuroceridae of the Atlantic coastal plain.  Occasional Papers of the Museum of Zoology, University of Michigan 456: 1 – 6.  For an appreciation, see:

  • The Legacy of Calvin Goodrich [23Jan07]

[3] To the German naturalist Johann Friedrich Gmelin goes the honor of describing the first freshwater gastropod endemic to North America, “Buccinum” (Pleurocera) virginicum in 1791.

[4] Bruguière, Jean Guillaume (1792) Vermes ('worms') in Daubenton's Encyclopédie Méthodique.

[5]  Morrison, J. P. E. (1954) The relationships of Old and New World Melanians. Proc. U. S. Nat. Mus. 103: 357- 394.  For context, see:

  • Joe Morrison and the great Pleurocera controversy [10Nov10]

[6] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.  For a thumbnail biography, see down below in my Isaac Lea bio:

  • Isaac Lea Drives Me Nuts [5Nov19]

[7] Walker, B. (1918)  A synopsis of the classification of the freshwater Mollusca of North America, North of Mexico, and a catalogue of the more recently described species, with notes.  Univ. Mich. Mus. Zool. Misc. Publ. 6: 1 - 213.  For an appreciation, see:

  • Bryant Walker’s sense of fairness [9Nov12]

[8] Parodiz, J. J. 1956.  Notes on the freshwater snail Leptoxis (Mudalia) carinata.  Annals of the Carnegie Museum 33: 391 - 405.

[9] Clench, W.J. and K. J. Boss (1967) Freshwater Mollusca from James River, Va., and a new name for Mudalia of authors.  Nautilus 80: 99 – 102.

[10] But Ken Boss was never going to win me as a graduate student, in any case.  George Davis had greatly impressed me at the AMU meeting in the summer of 1976, and was a very gracious host in Philadelphia, and I was hooked.  Burch had the early lead, but by the winter of 1976-77 had blown it

[11] Dillon, R. T., Jr. (1977) Factors in the distributional ecology of upper New River mollusks (Va/NC).  Undergraduate Research Thesis, Virginia Tech, Blacksburg. 59 pp.  [pdf]

[12] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

[13] Actually, He did, for numbers two and four only.  But for the rationale of number two, at least, it is difficult to be thankful.

[14] Goodrich, C. 1940. The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[15]  Well, the older I get, the more convinced I become that extensive pleurocerid ranges such as those displayed by Leptoxis carinata and Pleurocera proxima are the product of great age and extremely unlikely aerial dispersal events.  See the “jetlagged wildebison model” here:

  • Mitochondrial superheterogeneity: What it means [6Apr16]
  • Accelerating the snail’s pace, 2012 [24Apr17]

[16] Dillon, R. T., Jr. and J. D. Robinson (2009)  The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?  Journal of the North American Benthological Society 28: 1 - 11.  (Rosemary Mackay Award)  [pdf]  For more, see:

  • The snails the dinosaurs saw [16Mar09]

[17] The ultimate cause may have been sloppiness.  There is a line space missing between Goodrich’s treatment of Anculosa praerosa and his treatment of Anculosa subglobosa at the bottom of page 20 in his 1940 paper, which pulls subglobosa up underneath Goodrich’s list of nine praerosa synonyms.  Is it possible that Burch thought Goodrich was listing subglobosa as a tenth?

[18] Dillon, R. T., and S. A. Ahlstedt (1997) Verification of the specific status of the endangered Anthony's River Snail, Athearnia anthonyi, using allozyme electrophoresis. The Nautilus 110: 97 - 101. [pdf]

[19] Dillon, R.T., and C. Lydeard (1998) Divergence among Mobile Basin populations of the pleurocerid snail genus, Leptoxis, estimated by allozyme electrophoresis.  Malacologia. 39: 111-119. [pdf]  For more, see:

  • Mobile Basin II: Leptoxis lessons [15Sept09]
  • Intrapopulation gene flow, the Leptoxis of the Cahaba, and the striking of matches [2Nov21]

[20] Morrison, J. (1971) Athearnia a new name for a genus of pleurocerid snails.  The Nautilus 84:110 – 111.

[21] U.S. Fish and Wildlife Service (1994) Endangered and threatened wildlife and Plants; Determination of endangered status for the Royal Snail and Anthony’s Riversnail.  Federal Register 59: 17994 – 17998.  [FR-1994-04-15]

[22] This sort of thing pisses me off royally.  Science and public policy are not compatible.  And anybody who thinks otherwise is sharpening a knife to kill the former.

Tuesday, March 7, 2023

Malacological Mysteries: What was Planorbis glabratus?

In Volume 1 of the Journal of the Academy of Natural Sciences of Philadelphia, Part 2 (June 1818) The Father of American Malacology, Thomas Say, described a new freshwater gastropod as follows [1]:

Planorbis glabratus.—Shell sinistral; whorls about five, glabrous or obsoletely rugose, polished, destitute of any appearance of carina; spire perfectly regular, a little concave ; umbilicus large, regularly and deeply concave, exhibiting all the volutions to the summit; aperture declining, remarkably oblique with respect to the transverse diameter.

Breadth nearly nine-tenths of an inch. Inhabits South Carolina. Cabinet of the Academy.

Presented to the Academy by Mr. L'Hermenier of Charleston, an intelligent and zealous naturalist; he assured me that this species inhabits near Charleston. It somewhat resembles large specimens of the P. trivolvis of the American edition of Nicholson's Encyc., but differs in the total absence of carina, and in having a more smooth and polished surface, as well as a declining and more oblique aperture, and a more profound and much more regularly concave umbilicus.

Alas, Thomas Say did not offer us a figure of his new planorbid species, and alack, all of Say’s type material has been lost.  The 139 words I have quoted above are the sum total of everything we know for a fact about Planorbis glabratus.

But to be fair, as strings of 139 words go, Say’s 139 are pretty darn vivid.  The adjectives “glabrous” and “polished” effectively distinguish the shell of Say’s new planorbid from his (1817) P. trivolvis [2], widely distributed across North America.  “Nine tenths of an inch” is unusually large for a planorbid, and “whorls about five” suggests an exceptionally tight coil.

Planorbis glabratus from Haldeman [3] and Binney [4]

In any case.  Two monographers of the nineteenth century, Haldeman in 1844 [3] and Binney in 1865 [4], took shots at publishing figures of Planorbis glabratus, the former at left above, the latter at right.  Neither author offered a scale bar or a measurement, implying a 1:1 reproduction.  Both of those figures appear to depict shells with zillions of fine ridges, which make them look suspiciously like dirt common Helisoma trivolvis [5].

Henry Pilsbry wasn’t buying it.  We have already reviewed at great length, in three posts to date and counting, The Elderly Emperor’s landmark paper of 1934 [6] describing Seminolina as a new Floridian subgenus of Helisoma and assigning to it four species, including scalare (Jay 1839) and duryi (Wetherby 1879).  Pilsbry recognized three subspecies of duryi previously described and added three fresh ones, including a new scalariform (“flat topped”) subspecies seminole, about which we obsessed last month.  And he also described a new subspecies at the other end of the spectrum, Helisoma duryi eudiscus, bearing a broad, compressed, tightly coiled shell, shown in the figure below.  And he observed:

“This form [eudiscus] is what Bryant Walker [7] and the writer [Pilsbry] called Planorbis glabratus Say.  None of the specimens seen approach the dimensions given by Say, and the locality given by him is over 200 miles northward.  I have elsewhere discussed the identification of his [Say’s] species.”
H. duryi eudiscus [6]

That “elsewhere” turned out to be “immediately following.”  Because the next section of his 1934 paper was headed, “Species Recorded from Florida in Error.”  Here Pilsbry elaborated the opinion (first expressed by Wetherby) that neither the shell figured by Haldeman, nor the shell figured by Binney, matched Thomas Say’s original description.  And he agreed with Wetherby that South Florida is indeed inhabited by populations of large, flat, shiny, tightly coiled Helisoma that do match Say’s description, which (he had just suggested) might be identified as Helisoma duryi eudiscus.  But…

“A difficulty with this identification [of eudiscus as glabrata] is that no such shell has been found in Georgia or in South Carolina (Say’s locality); and there is little probability that a shell from the lower and middle parts of peninsular Florida would have been collected prior to 1818.”

Let me repeat that.  That is important.  Pilsbry himself, and Bryant Walker, and Albert Wetherby, all thought that the shells borne by planorbid populations Pilsbry was describing as Helisoma duryi eudiscus matched Say’s description of Planorbis glabratus.  But Pilsbry did not think that Helisoma duryi ranged as far north as Charleston.  And he didn’t know of any eudiscus anywhere reaching a diameter approaching “nine-tenths of an inch” in any case.  Remember all that.  You’re going to need it after the intermission.

Pilsbry then went on to propose a rather elaborate hypothesis, as follows:

“Say received the type specimen of P. glabratus from Mr. L'Herminier of Charleston, S. C. His description applies well to the Antillean Planorbis guadaloupensis Sowb. I was thus led to inquire into the travels of L'Herminier. I applied to Mr. E. B. Chamberlain, Director of the Charleston Museum, who [confirmed that L’Herminier] came to Charleston about 1814 from Guadeloupe bringing 'an extensive collection of specimens, the fruit of twenty years application, expense and industry, which he offered to the Society [The Literary and Philosophical Society of South Carolina]. Dr. L'Herminier was appointed superintendent or curator of the Society's museum, and served until 1819, at which time he returned to Guadeloupe. […] It seems quite likely therefore that the type of Planorbis glabratus was one of the specimens L'Herminier brought from Guadeloupe, and which he subsequently thought (or Say inferred) that he had picked up around Charleston.”

I know it must seem to you, my loyal and longsuffering readership, that your eccentric guide to malacological triviality most arcane has developed an obsession most inexplicable with an obscure 1934 paper published in the Proceedings of the Academy of Natural Sciences of Philadelphia, having posted three essays dwelling on the work thus far, plus a large fraction of a fourth essay presently unfolding.  Why, you must be wondering, can’t you let those 44 pages of densely-packed esoterica go, Dillon, for God sake?  Well, I regret to inform my readership, we haven’t even touched the more important half of Pilsbry’s 1934 paper yet.

Pilsbry’s full title was, “Review of the Planorbidae of Florida, with Notes on Other Members of the Family.”  And by “notes,” Pilsbry meant to propose a taxonomic revision of the entire planorbid fauna of the New World.

Australorbis glabratus [6]
So, in the second half of his paper, Pilsbry recognized eight previously described genera in The Americas: Tropicorbis and Drepanotrema from Way Down South, Carinifex and Parapholyx from Way Out West, and our old friends from right here at home: Helisoma, Planorbula, Menetus and Gyraulus.  To these he added a ninth genus, a newly described Australorbis.  And as the type of his new genus, he selected “P. guadaloupensis Sowb. = A. glabratus (Say).”

The population of “P. guadeloupensis = A. glabratus” that Pilsbry examined was collected from Puerto Rico.  They bore large, flat, shiny, tightly coiled planispiral shells not much different from the Florida populations that he and Wetherby and everybody else had been identifying as Helisoma duryi, especially the subspecies “eudiscus.”  But anatomically the Puerto Rico population was quite distinct from Helisoma, missing a penial gland entirely [8].

Both Baker in 1945 [9] and Hubendick in 1955 [10] accepted Pilsbry’s Guadeloupe hypothesis for the origin of Thomas Say’s Planorbis glabratus uncritically, which pretty much set it in concrete, and both accepted Australorbis as a natural genus in which to place it.  Baker dissected and figured his sample from Puerto Rico; Hubendick’s came from Venezuela.  Baker also gathered a fairly large list of synonyms under glabratus, beyond the guadeloupensis suggested by Pilsbry, including olivaceus (Spix) from Brazil, refulgens (Dunker) from Santo Domingo, lugubris (Wagner) from Surinam, and blauneri (Germain) from Venezuela.  So, by 1955, the range of Australorbis glabratus was given as Venezuela to Argentina and throughout the Caribbean.

Yet another taxonomic change was looming, however, even as Hubendick labored over his 1955 monograph.  In 1910, the Englishman H.B. Preston had proposed the genus Biomphalaria to hold his new Biomphalaria smithi from the Congo/Uganda border [11], and during the 40 years that followed, momentum built to allocate an increasing number of African species to Preston’s genus.  And indeed, species from the New World as well.  Hubendick wrote:

"The Biomphalaria tribe includes the following genera: Biomphalaria, Afroplanorbis, Australorbis, Tropicorbis, Taphius, and Platytaphias and probably Syrioplanorbis…The whole tribe is anatomically so homogeneous that it is doubtful if the present separation into genera can be maintained.”

Doubtful, indeed.  Begging your indulgence, please allow me to back up and get a fresh start on this entire story, from an entirely fresh perspective [12].  In 1851 the German physician Theodor Bilharz discovered that a widespread and debilitating disease affecting a large fraction of the population of Egypt was caused by a parasitic worm.  And in 1915 the Scottish physician Robert Thomson Leiper identified two species of the digenetic trematode genus Schistosoma as the helminthological culprits for two different forms of this same disease and simultaneously worked out the intermediate hosts for both: “Planorbis boissyi” for Schistosoma mansoni and “Bulinus spp” for Schistosoma haematobium.

The form of the disease caused by Schistosoma mansoni had also been a problem for many years in the New World tropics, as well as in the Old.  And in 1916, almost immediately after Lieper published his results on Schistosoma mansoni in Egypt, the Brazilian Adolpho Lutz reported the successful development of S. mansoni miricidia in a snail he identified as “Planorbis olivaceus = P. bahiensis.”   Then in 1917, the Venezuelan Juan Iturbe obtained similar results with a planorbid population he identified as “Planorbis guadelupensis.”

From Castillo et al. [13]

Was Pilsbry unaware of Iturbe’s research when he synonymized Planorbis guadelupenis under Australorbis glabratus?  Was Baker unaware of Lutz’s work when he did the same thing to Planorbis olivaceus?  Neither Pilsbry nor Baker mentioned anything about the parasitological importance of the taxonomic judgements they were making.  But together, they made Australorbis glabratus into a Latin binomen that appeared in the abstracts of scores of papers directly bearing on issues of human health through the 1940s into the early 50s.

By 1955, Hubendick did think it worth mention that “several planorbids act as intermediate hosts for many trematodes, including schistosomes” in his introduction,  although he did not hear the call to develop that theme until the 84th page of his 90 page work.  There he reiterated his opinion that Australorbis (and Tropicorbis) did not differ “in any essential way” from Biomphalaria (or Afroplanorbis).  But he continued, “although the most natural course would be to unite all the genera into one genus,” to do so “would certainly cause much confusion and trouble to works in medical parasitology who are now familiar with names which are in current use.”  Thus, Hubendick advocated retaining glabrata (Say 1818) in Australorbis.

All I can figure is that by the time he wrote those words, Hubendick had already been out-voted.  Because in 1954 the World Health Organization had convened an international “Study-Group” consisting of Alves, Berry, Hubendick, LeRoux, Mandahl-Barth and Ranson.  And by 1955, the joint opinion of the group had been published [14]:

“It has long been recognized that the known species which serve as the intermediate hosts for S. mansoni are genetically the same and that all have probably been derived from common stock.  It was therefore agreed that these and their related species should be united into a single genus Biomphalaria, and that the genera Australorbis, Afroplanorbis, and Tropicorbis should be considered synonyms.”

And all other researchers worldwide fell in line.  So today, a quick reference to the NCBI PubMed database returns 3,438 hits to the search term “Biomphalaria glabrata,” the intermediate host of schistosomiasis in the New World, 1947 to present.

OK, I’m going to take a 20-minute break for some fresh air.  While I’m gone, here’s a question for your consideration.  What would happen if Thomas Say’s sample of Planorbis glabrata really was collected from Charleston, as he was assured by that “intelligent and zealous naturalist,” Felix L'Hermenier?  Discuss amongst yourselves …

… and I’m back.  I just drove over to Charles Towne Landing State Park, about a mile from my house here in the West Ashley neighborhood of Charleston.  They have a couple pretty little spring-fed lakes over there.  And the figure below shows what I found.

These shells are a near-perfect match to every word in Thomas Say’s 1818 description of Planorbis glabratus, and don’t tell me that they aren’t.  They are “destitute of any appearance of carina,” “polished” to the point of “glabrous.”  Their spires are (indeed) “a little concave, umbilicus large,” and apertures (indeed) “remarkably oblique.”  The diameter of the middle specimen, viewed edge-on, is 22.6 mm = 0.89 inch.

This is the "Population C" I sampled for our colleague Cindy Norton back in 2018.  My readership will remember that Cindy's breeding experiments returned no evidence of reproductive isolation between population C and a sample of Helisoma scalare scalare (“F”) I collected for her from way down in the Florida Everglades [15].  So, since the shells borne by Population C are planispiral, the most modern, least-controversial identification for the Charles Towne Landing population is currently Helisoma scalare duryi [16].

Charles Towne Landing SP
But might they be Planorbis glabratus?  The only quibble one might offer to the identification of Population C as P. glabratus could be the whorl count, which Say described as “about five.”  I really can’t count more than four whorls in the shells figured at left.  But it turns out that other populations here in the Charleston area do sometimes bear much narrower, more tightly coiled shells demonstrating five whorls and more. 

The figure at the top of the montage down below was borrowed from a [29Nov04] essay I wrote about a gigantic Helisoma population inhabiting an ornamental pond outside a commercial office park here West of the Ashley, about a mile from Charles Towne Landing.  And the two figures beneath it were borrowed from a [18Feb05] essay I wrote about a dimorphic Helisoma population in a subdivision called “Wakendaw Lakes” in Mt Pleasant, a Charleston suburb east of the Cooper River.  I initially identified both of those populations as “Helisoma trivolvis,” back before the scales fell from my eyes in 2021 [17], but their best modern identification would again be Helisoma scalare duryi, same as the Charles Towne Landing population.

Pilsbry and Baker would almost certainly have identified the shells from Charles Towne Landing State Park above as Helisoma duryi normale [16].  Those from the office park and the Wakendaw Lakes subdivision below I feel fairly certain would have been Helisoma duryi eudiscus.  And both Pilsbry and Baker would have been shocked to learn that any planorbid populations bearing shells of such flamboyantly duryi morphology might inhabit waters anywhere north of Florida [18].

But in fact, I am now aware of six populations of H. scalare duryi in Charleston County alone, and many others scattered elsewhere around coastal South Carolina as far north as the vicinity of Myrtle Beach, and three in coastal Georgia as well [19].  Plus, Binney’s historic record from St. Simon’s Island, GA, brings the Georgia populations up to four [5].

Although most of the Carolina and Georgia populations of H. scalare duryi of which I am aware inhabit disturbed environments today, my biological intuition suggests to me that this northern end of their range is as natural as their southern one.  Binney’s collection dates prior to 1865.  But even if the occurrence of Helisoma scalare duryi here in the Charleston area is artificial, if the introduction occurred prior to 1818, the point I am trying to argue will not be affected.

Office Park & Wakendaw
Here in 2023 there is no reason to doubt that the shells in Thomas Say’s hand when he described Planorbis glabratus in 1818 were, indeed, collected in Charleston, South Carolina, as the “intelligent and zealous naturalist” Felix L'Hermenier assured him.  Pilsbry’s (1934) hypothesis that L’Hermenier’s shells came from Guadeloupe was predicated on Pilsbry’s erroneous belief that Helisoma duryi, specifically the tightly compressed subspecies he described as H. duryi eudiscus, did not range north of Florida.  Now that we know that such populations do, in fact, inhabit many ponds in the Charleston area, identified as Helisoma scalare duryi today, Pilsbry’s Guadeloupe hypothesis has become entirely unnecessary.

So by the letter of the International Code of Zoological Nomenclature, all those Floridian nomina of planorbids: scalare (Jay 1839), duryi (Wetherby 1879), and all the subspecies proposed by Pilsbry and others, like eudiscus and seminole, are junior synonyms of glabrata (Say 1818).  Which means that by the letter of the Code of Zoological Nomenclature, all those tropical planorbid populations that host Schistosoma mansoni in the New World, originally identified as guadeloupensis (Sowerby), olivacea (Spix) and many other names [20], are not correctly identified as Biomphalaria glabrata.  They must be called something else.  I don’t know what.  I don’t want to know.

Because what I have uncovered here is a bomb.  Actually, it’s more like one of those rusty old artillery rounds that utility crews still occasionally dig up under the streets of Charleston, fired by Union cannon during the bombardment of 1863-65.  It’s a dud.  That old thing can’t possibly be dangerous, can it?

Well, yes, it can.  I myself was caught in the shrapnel when Jack Burch unearthed just such a dud in the early 1980s [22].  The genus Elimia was shot into the air by H & A Adams in 1854 to contain an odd-lot assortment of pleurocerid nomina, hit the ground with a thud, and was buried and forgotten for 120 years, explicitly rejected by Tryon, Walker, Goodrich, and all other authorities of the day in favor of Isaac Lea’s Goniobasis.  But even as I was defending my dissertation on Goniobasis in Philadelphia, Jack Burch was exhuming Elimia in Ann Arbor and synonymizing Goniobasis underneath it.  This he did for no scientific reason whatsoever, motivated entirely by a sense of romantic duty to the Code of Zoological Nomenclature.  The confusion and misunderstanding persist to the day [23].

So, it turns out that when Charleston utility crews unearth unexploded Yankee ordinance, no matter how old and decrepit the round might be, they don’t rebury it.  They call the bomb squad.  And the bomb squad doesn’t try to “defuse” that rusty old thing in some fine and sophisticated manner.  They just blow it up.

So, this month I have spent 3,028 words digging up a rusty old bomb called “Planorbis glabratus.”  I now mean to blow it up.  Planorbis glabratus Say 1818 must remain a senior synonym of Planorbis guadeloupensis Sowerby, 1822, as proposed by Pilsbry in 1934, and senior as well over all tropical and Caribbean planorbid taxa more recently described and subsequently placed underneath it [20].  To redefine Say’s 1818 taxon as a senior synonym of John Clarkson Jay’s 1839 Paludina scalaris or Wetherby’s 1879 Helisoma duryi would be a terrible disservice to the cause of science.  I won’t do it, and don’t any of the rest of you try.

Because here’s the important thing.  And I am dead serious about this, so listen up.  Biological nomenclature must serve science.  To change the specific name by which we have referred to the intermediate host of schistosomiasis in the New World would create epic levels of confusion, mischief, and mayhem for absolutely, utterly no reason other than an obscure point of law.  Biomphalaria glabrata must remain Biomphalaria glabrata, as that taxon is currently understood by the scientific community, for the sake of science, now and forever, amen.


[1] Say, T. (1818) Account of two new genera, and several new species, of fresh water and land shells.  Journal of the Academy of Natural Sciences of Philadelphia 1(2): 276 – 284.

[2] The shell of Helisoma trivolvis is “thread striate,” noticeable especially in juveniles, which tends yield a duller luster.  See:

  • Collected in Turn One [5Jan21]

[3] Haldeman, S.S. (1844) [not “1841”] A monograph of the freshwater univalve Mollusca of the United States, Number 7  Philadelphia: Cary & Hart, Dobson, and Pennington. 32 pp, 4 plates.

[4] Binney, W.G. (1865) Land and fresh water shells of North America Part II, Pulmonata Limnophila and Thalassophila. Smithsonian Miscellaneous Collections 143: 1 – 161.

[5] Haldeman’s specimen came from “Mexico (?)” and Binney’s specimen came from St. Simon’s Island, GA, which means, ironically, that Binney’s (at least) was almost certainly correctly identified as Planorbis glabratus, in the contemporary meaning of that name.  Read on and see footnote [17].

[6] Pilsbry, H. A. (1934) Review of the Planorbidae of Florida, with notes on other members of the family.  Proceedings of the Academy of Natural Sciences of Philadelphia 86: 29 – 66.  For a review, see:

  • The Emperor Speaks [3Dec20]
  • The Emperor, the Non-child, and the Not-short Duct [9Feb21]
  • New Clothes for The Emperor [7Feb23]

[7] Walker, B. (1918) A synopsis of the classification of the freshwater Mollusca of North America, North of Mexico, and a catalogue of the more recently described species, with notes.  Univ. Mich. Mus. Zool. Misc. Publ. 6: 1 - 213.

[8] The distinction between Pilsbry’s new genus Australorbis and his previously described Tropicorbis was negligible, however.  And I quote: “P. guadaloupensis differs from Tropicorbis by its extremely short almost sessile spermatheca, the relatively shorter upper sac of the penis, and by the denticulation of the marginal teeth, in which the denticles remain widely separated in an inner and an outer series.”  Good grief.

[9] Baker, F.C. (1945) The Molluscan Family Planorbidae. Urbana: University of Illinois Press.  530 pp.

[10] Hubendick, B. (1955) Phylogeny in the Planorbidae. Trans. Zool. Soc. London 28: 453-542.

[11] Preston, H. B. (1910). Additions to the non-marine molluscan fauna of British and German East Africa and Lake Albert Edward. The Annals and Magazine of Natural History. (8) 6 (35): 526-536, pl. 7-9.

[12] I thank Sam Loker for pointing me to an excellent reference on the history of schistosomiasis research, upon which I have based the brief review above:

  • Grove, David I. (1990) A History of Human Helminthology. C.A.B.International, Wallingford.

[13] Castillo, M.G., J.E. Humphries, M.M. Mourao, J. Marquez, A. Gonzalez, C.E. Montelongo (2020) Biomphalaria glabrata immunity: Post-genome advances.  Developmental & Comparative Immunology 104: 103557.

[14] Alves, W., E.G. Berry, B. Hubendick, P.L. LeRoux, G. Mandahl-Barth, and G. Ranson (1954). Bilharzia snail vector identification and classification (Equatorial and South Africa).  Report of a Study-Group.  World Health Organization Technical Report Series 90: 1 – 24.

[15] For the complete story of Cindy Norton’s breeding experiments, read this series of essays:

  • The Flat-topped Helisoma of The Everglades [5Oct20]
  • Foolish Things with Helisoma duryi [9Nov20]
  • Collected in Turn One [5Jan21]

[16] I just proposed lowering Wetherby’s (1879) duryi to subspecific status under Jay’s (1839) scalaris last month.  But the build-up was a lengthy one, extending back to early 2021.  Work backwards from this essay if you want the complete

  • New Clothes for the Emperor [7Feb23]

[17] Although I reported the “scales falling from my eyes” regarding the Charleston area Helisoma populations in January of 2021, the build-up was a lengthy one, extending back to 2018.  Work backwards from this essay if you want the complete story:

  • Collected in Turn One [5Jan21]

[18] In my dreams, I march right up to Philadelphia with a Charleston sample of Helisoma scalare duryi under my arm and present it to Henry Pilsbry.  He accepts it, thanks me, and writes, “another notorious liar” on the back of the label.

  • Dr. Henry A. Pilsbry was a Jackass [26Jan21]

[19] Toward the bottom of my 5Jan21 essay, I mentioned “one population of H. duryi in coastal Georgia" as well as “15 populations in coastal South Carolina.”  More recently I have discovered two additional populations of H. scalare duryi in Savannah, bringing the coastal Georgia count up to three.

[20] Here’s a list of junior synonyms that have been placed under glabrata (Say 1818), collected both from Baker [9] and from Malek [21]guadeloupensis (Sowerby), christopherensis (Pils), olivaceus (Spix), refulgens (Dunker), lugubris (Wagner), blauneri (Germain), ferrugineus (Spix), nigricans (Spix), albescens (Spix), viridis (Spix), lundii (Beck), cumingianus Dunker, becki Dunker, bahiensis Dunker, and xerampelinus Drouet.

[21] Malek, E. (1985)  Snail hosts of schistosomiasis and other snail-transmitted diseases in tropical America: A manual. Washington, D.C., Pan American Health Organization.  325 pp.

[22] For a complete review of the controversy, see:

[23] The controversy should have ended in 2011, when I formally synonymized both Goniobasis and Elimia under Pleurocera, but it did not.  See:

  • Goodbye Goniobasis, Farewell Elimia [23Mar11]