Dr. Rob Dillon, Coordinator





Wednesday, September 9, 2020

Juvenile Helisoma


Before launching into the subject of this month’s essay, I do want to emphasize that I always enjoy hearing from you.  I’m retired, and bored, and I (honestly!) do not have a whole lot better to do than sit at my computer and correspond with colleagues from around the world, about a subject that has fascinated me since childhood.  So let’s open up the Ol’ Mailbag and see what the postman brings.  Click the captions under the thumbnail jpegs to see the larger, original images:

Greetings Dr. Dillon:

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We have collected an aquatic snail that has puzzled me for years (photo attached).  At first, it seemed unique enough that we could record it without paying much attention to biogeography.  We used the genus Planorbella (based on Burch’s EPA publication) to document the counts when we collected it during bioassessment work.  Since I began working on aquatic snail distribution, I have tried to get better at snail IDs and to possibly learn a little.

Thanks for any feedback that you might provide!
[Baffled in Missouri]

Hello Dr. Dillon,

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I hope this email finds you well.  I'm afraid I'm cold-emailing you (if such a thing exists) to ask for advice re: some gastropods I'm keying out as a small cog of a [federally-funded] monitoring program […] Finally, my other big headache is my stubborn inability to feel comfortable IDing to genus the small Planorbidae down to genera.  I had a weird Helisoma this year, with bizarre whorling too. It happens, I guess! […] So I'd like to ask if you'd be kind enough to peek at a few pictures (in .zip form) I've attached of stubborn-to-ID snails.

Much obliged,
[Bothered in Indiana]

Dear Robert,

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You may remember me. I contacted you about [another question] in 2011.  I have another riddle to submit to you.  We sampled those gastropods in a small river in Quebec.  We’ve never seen that before. It looks like some Amerianna or Planorbella that are not present in our region.  Can you tell me the identification? They can come from an aquarium?

Thanks for your help,
[Bewildered in Quebec]

Dear Baffled, Bothered, and Bewildered,

The snails depicted in all your jpegs are juvenile Helisoma trivolvis.  They don’t look much like adults, do they?

Their most striking feature is that flat apex, when viewed sinistrally, which is the way you have all depicted them, which is the correct.  Helisoma anceps, by contrast, has an indented apex when viewed sinistrally, even as a juvenile.  Indeed, the apex of H. anceps is indented no matter how you look at it, which makes anceps shells pretty darn near perfectly-planispiral.  But trivolvis is unambiguously sinistral.

Both H. trivolvis and H. anceps can be found anywhere, but H. trivolvis is a better floater, and is more common in lentic environments, especially in macrophytic vegetation.  Helisoma anceps is more common in lotic environments – especially in calm backwaters – generally grazing on solid substrates.  See the figure below for a comparison of juvenile H. trivolvis, H. anceps, and H. campanulatum, from up north, included here for completeness.

Have you ever heard the old saw [1], “Ontogeny recapitulates phylogeny?”  Planorbids evolved from a left-handed ancestor that probably looked something like a modern physid.  Through subsequent selection they have evolved planispiral shells – possibly so that the air bubble enfolded by their shells forms a more stable float – and in the adults of many species it is now difficult to see which way their shells are coiling, left or right.

But in Helisoma trivolvis, newly-hatched juveniles do show an apex (flat-topped but still distinct) and (hence) are very obviously sinistral.  As they mature, they flip their shells across their backs and become more planispiral, losing their apparent axis of coiling.  Usually.  But there’s a big asterisk to that generalization.

More to follow!
Rob

The shells of juvenile Helisoma
At this point in my essay, allow me to speak directly to you, the readership of this blog, rather than as a correspondent to a third party.  I did a bit of a disservice to our colleague Baffled-in-Missouri at the top of this essay.  His email continued with a lot of excellent insights and additional questions, from which I have extracted the following:
“If you have the time and interest to respond, I would like your opinion about the following speculations: Following your modified classification of Hubendick [2], I would lean toward calling the snails in my photo Helisoma scalare, or possibly Helisoma duryi.  Since I now realize that these species are from Florida, I would have to suspect an introduction to Missouri.  There seems to be several scientific journal articles to support the idea of a possible aquarium introduction of these species worldwide. […] The other possibility is one you have written about many times.  Do you think phenotypic plasticity is a possibility?  Many times, we also have co-occurring records of Helisoma sp. that have the more typical form.  This form always seems to be the more mature individuals.  Even if not fully grown, the typical form is always much larger that the Helisoma scalare form.”
Here Baffled-in-Missouri has broadened the subject in an interesting direction – adult shell morphology.  He is referring to an essay I contributed to this blog way back in 2005, sharing my observations on a single Helisoma trivolvis population inhabiting two strikingly-different environments in the “Wakendaw Lakes” subdivision on the other side of the Cooper River from Charleston [3].  It might help to open that essay in another window and keep my photo of that study area handy [15Feb05].

While the H. trivolvis inhabiting the little retention pond upstream demonstrate typical shell morphology, those that have colonized rip-rap rocks in the flowing-water environment below the pond retain their flat-topped, obviously-sinistral juvenile morphology into adulthood.  Here’s an improved version of the figure I originally published in 2005, which I fixed up for my 2019 book [4]:

Helisoma trivolvis population of Wakendaw Lakes
That’s quite a vivid demonstration of ecophenotypic plasticity [5], isn’t it?  Both shells are from adults, photographed at the same scale.  Snails in the pond above the dam are grazing in the macrophytic vegetation, using their shells as buoyant floats, like normal.  Snails below the dam are grazing on rocks, holding their shells low on their backs against the current.

And here is the most interesting thing about this phenomenon, to me, anyway.  The snails on the rocks, retaining their juvenile shell morphology into adulthood as they do, look sinistral, as planorbids actually are.  But the H. trivolvis inhabiting the pond, have (as is typical for the species) flipped their shells so far across their backs that they seem to have gone beyond planispiral to dextral.  Typical pond-dwelling H. trivolvis look “right” the way I have depicted them above.  I’m not sure why this is so, but turn your computer monitor upside down and look at the  pond-dwelling snails again if you don’t believe me.  Or just look back at the original figure in my 2005 post, where the typical H. trivolvis shell looks like it's upside down.

That, by the way, is why “Planorbella” is (at best) a subgenus under Helisoma.  The distinction (originally drawn by Baker [6]) has to do with whether the adult is apparently right-handed or apparently left-handed, a trait which can vary within a single population, ecophenotypically.

So Baffled-in-Missouri also brought up the question of Helisoma scalaris/scalare and Helisoma duryi, which I myself also touched upon in 2005.  Those are Florida species, primarily distinguished by their flat-topped, sinistral-looking shell morphology carried into adulthood.  What, exactly, are Helisoma scalaris and Helisoma duryi?  Tune in next time.


Notes:

[1] That phrase, originally coined by Ernst Haeckel, has pre-Darwinian roots.  It was appropriated by twentieth-century philosophers and charlatans (most notably Stephen Jay Gould) and twisted every way it could possibly be twisted, to the point that nobody knows what it means, much less whether Haeckel’s theory has any validity or not.  Wikipedia has a pretty standard review if you want to google it.

[2] Hubendick, B. (1955) Phylogeny in the Planorbidae. Trans. Zool. Soc. London 28: 453-542.  For a modern elaboration, see:
  • The Classification of The Planorbidae [11Apr08]
[3] More about the Helisoma trivolvis population of Wakendaw Lakes:
  • Shell morphology, current, and substrate [18Feb05]
[4] My 18Feb05 essay was subsequently published as:
Dillon, R.T., Jr. (2019b)  Shell morphology, current, and substrate.  Pp 121-126 in Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston. [FWGNA Publications]

[5] This present essay is the 28th I have published on the ever-fascinating subject of ecophenotypic plasticity in freshwater gastropod shell morphology.  Hit the “Phenotypic Plasticity” label in the margin at right if you don’t believe me.  My series on the stagnicoline lymnaeids is probably the most relevant.  Start at the end, here:
  • The Lost Thesis of Samantha Flowers [3Sept15]
[6] Baker, F. C. (1945) The Molluscan Family Planorbidae. University of Illinois Press, Urbana. 530 pp.  For more about my hero, see:
  • The Legacy of Frank Collins Baker [20Nov06]

Monday, August 3, 2020

Mitochondrial heterogeneity in Marstonia lustrica

A raised-letter certificate of appreciation, with wax seal and red ribbon, is hereby awarded our good friend Tom Coote for his important contribution to the general understanding of mtDNA sequence divergence in the freshwater gastropod fauna of North America.  The paper he based on his 2011 dissertation [1], published late last year in Northeastern Naturalist [2], offers us the best survey of intraspecific mtDNA sequence variation among hydrobioid populations as yet available, anywhere [3].  His results will surprise many and enlighten us all.

Populations of the (relatively large-bodied) Marstonia lustrica can reach locally high densities on rocks and macrophytes in big lakes and other cold, clear bodies of water above the glacial maximum.  In recent years they have disappeared from many habitats where they were once common [eg Oneida Lake, 6] and hence have been the object of some conservation concern.  Our buddy Tom obtained COI and NDI sequences from 20 M. lustrica populations scattered across six northern states and one Canadian province.  He recorded at least one COI sequence from 18 of those 20 populations, for a total of 54 sequences.  And he recorded at least one NDI sequence in 14 of the 20, including the two populations that he missed with the COI, for a total of 41 sequences.

Let us first look at Tom’s COI results.  That big black triangle at the top of his maximum likelihood COI tree below (labelled “modal”) represents the most common sequence, and variants of no greater than 0.5%, which he recorded in 39 of his 54 individuals.  Tom documented at least one copy of the modal sequence in 15 of the 18 populations for which he had any COI data.

Sample sites, from Coote [2]

Now look immediately below the black triangle.  The three sequences marked “HLMN,” from Harriet Lake, Minnesota, differed from the modal sequence by 1.4%.  And the sequences marked KBMI (B and C, from Keeweenaw Bay, in Lake Superior) differed from the mode by 0.5%.  And the sequences marked LLMN, from Limestone Lake, MN, differed from the mode by 2.6%, and so forth.  The maximum divergence from the mode was 4.5%, recorded by two sequences collected at Grand Island, New York (GINY-A and GINY-D) and the one collected in Indiana’s Tippicanoe River (TRIN).  The maximum COI divergence anywhere in Tom’s dataset was 5.7%, between GINY-A and IRMI-A, from Isle Royal in Lake Superior.

 Now perhaps the most striking features of Tom’s COI tree are the three branch tips circled in red.  These are not Marstonia lustrica.  These tips are occupied by sequences fished from GenBank for Marstonia pachyta (1.4% from modal M. lustrica), M. comalensis (3.0% from modal M. lustrica) and M. hershleri (2.7% from modal M. lustrica).  These three sequences, recorded from Marstonia populations in Alabama, Texas, and Alabama respectively, are nested inside Tom’s larger Marstonia lustrica COI tree.

Does this mean that Tom Coote has discovered a big swarm of new Marstonia species?  Does his TRIN/GINY sequence for example, 4.5% different from modal M. lustrica, sitting on its own branch of the tree, way outside three other good Marstonia species from Alabama and Texas, reveal to us the existence of an undescribed species of hydrobiid lurking in the Niagara River of upstate New York, cryptic under Marstonia lustrica?  No, of course not.

Because Tom obtained four COI sequences from the GINY population, and two of them (GINY-B and GINY-C) were modal.  The Marstonia lustrica population on the Grand Island shores of the Niagara River is heterogeneous for (at least) two COI sequences – the common one that is found everywhere across six northern states and a rare one, 4.5% different, that matches – if you can believe it – a population in Indiana.

COI maximum likelihood tree, from Coote [2]

Well, then.  How about that sequence Tom found at Moira Lake way up in Ontario (MLCA-B), the one that seems to match a Marstonia hershleri haplotype collected down in the Heart of Dixie?  Maybe Moira Lake is inhabited by an Alabama species?  No, of course not.  Because again, Tom obtained three COI sequences at Moira Lake, and two of them (MLCA-A and MLCA-C) were modal.  The Moira Lake population is heterogeneous for two COI haplotypes differing by 2.4%.

What could that mean?  Maybe Tom’s NDI results will cast some light on his peculiar COI data.  He did not publish his NDI results separately, preferring to offer us a concatenated COI+NDI network in his Northeastern Naturalist paper.  But the figure down below shows the NDI (only) neighbor-joining tree from his dissertation [1].

Good grief!  Sticking way out on a distant limb of Tom’s NDI tree we find the same three sequences that were sticking way out on that distant limb of his COI tree: GINY-A, GINY-D, and TRIN-A.  And again, GINY-B and GINY-C are lumped into the mode.  And there’s MLCA-B sticking way out as well, again with MLCA-A and MLCA-C in the mode.  Could the striking similarity of Tom’s COI and NDI trees be a coincidence?

No, of course not.  The two M. lustrica data sets we are comparing here correspond precisely as the COI and 16S data sets that Nathan Whelan and Ellen Strong developed for pleurocerids in Alabama [7] and published in 2016.  And indeed, Dillon & Frankis documented an identical correspondence between COI and 16S haplotypes in Pleurocera proxima of the Southern Appalachians way back in 2004 [8].

At this point I would invite you to open a new browser window and re-read my blog post of 15Mar16, entitled “Mitochondrial superheterogeneity: What we know.”  In that 2016 essay I reviewed the striking patterns of mtDNA sequence divergence reported by Whelan & Strong in North Alabama pleurocerids and compared them to a set of 18 other such studies published for a variety of other gastropod populations both terrestrial and freshwater.  Of the six bullet-points that Whelan & Strong confirmed for us (or taught us!) about mitochondrial superheterogeneity (mtSH), let me call your attention to #2, “peculiar patterns of interpopulation haplotype sharing” and #3, “tight coupling in the evolution and distribution of separate mitochondrial genes.”  Do those phenomena look familiar?

NDI Neighbor-joining tree, from Coote [1]

The patterns in mtDNA sequence divergence in Tom Coote’s M. lustrica populations correspond strikingly to the patterns that Whelan & Strong documented in the Leptoxis populations of North Alabama.  The only difference is one of scale: Marstonia lustrica haplotypes only vary to a maximum of 4.5% within populations, while intrapopulation sequence heterogeneity in Alabama pleurocerids ranges up to 20%, and elsewhere in the southern Appalachians up to 21.9% [9].

Marstonia populations sampled above the glacial maximum are younger than the pleurocerid populations of the American South.  I feel sure that M. lustrica, the original population of that species, diverged from whatever its ancestor might have been prior to the Pleistocene, probably up north somewhere, and that it spread, and that isolated populations diverged in a fashion not unlike the pleurocerids.  Glacial advance may well have extinguished the species through most of its range, to survive only in isolated refugia.  Populations have then subsequently re-colonized the northern latitudes, but not in a smooth wave rolling from south to north.  Rather, individual colonists have been airlifted north from genetically divergent refugia in a chaotic and unpredictable fashion, some lakes skipped and other lakes colonized twice.

I would now invite you to open another browser window and re-read my essay of 6Apr16, “Mitochondrial superheterogeneity: What it means.”  My “wildebison model” will be easy to recognize in the paragraph above.

And finally, I would invite you to review my essay of 3May16, “Mitochondrial superheterogeneity and speciation.”  Under the wildebison model of mtDNA genome evolution, we now understand that results such as Tom Coote has reported for COI and NDI do not call into question the specific identity of scattered Marstonia lustrica populations.  Just the opposite.  Strikingly divergent haplotypes such as he has labelled GINY-A and TRIN on the distant branches of his gene trees constitute direct, positive evidence that the Marstonia populations inhabiting the Grand Island shores of the Niagara River in upstate New York and the Tippencanoe River of Indiana are conspecific.

One last point, and then a summary, begging your indulgence.  All of my 2016 essays were directed toward the phenomenon of mitochondrial superheterogeneity, which I defined on 15Mar16 as follows: “A population can be said to demonstrate “mitochondrial superheterogeneity” when two or more of its members demonstrate 10% sequence divergence or greater for any single-copy mtDNA gene, not sex-linked.”  Well, Tom Coote’s Marstonia populations do not display mtSH by that definition.  Their maximum intrapopulation divergence (GINY-A and GINY-B) is just 4.5%.  So, let us call intrapopulation sequence divergence greater than 2% but less than 10% “simple mitochondrial heterogeneity” (mtH) nothing super about it, shall we?  I think future research will find mtH to be the rule in freshwater gastropod populations, not the exception.

Gene trees are dependent variables, not independent.  Examined in isolation, they can lead the na├»ve researcher to terrible misunderstandings about the evolution of the group which he studies.  But bringing a robust understanding of the evolution of the group to his study, a wise researcher can peer through the window of a gene tree to find evolutionary processes of great generality and importance.


Notes:

[1] Coote, T. W. (2011) The phylogeography of Marstonia lustrica: Understanding the relationship between glaciation and the evolution and distribution of a rare snail.  Ph.D. dissertation, University of Massachusetts, Amherst.  Open Access Dissertations 399. [html]

[2] Coote, T. W. (2019)  A phylogeny of Marstonia lustrica (Pilsbry 1890) (Gastropoda: Hydrobiidae) across its range.  Northeastern Naturalist 26: 672 – 683.

[3] Well, maybe I should back up and qualify my opening paragraph just a little bit.  Tom’s research involved more populations of any single hydrobioid species than have ever been heretofore surveyed, although not more individuals.  Tom Wilke and colleagues did publish, back in 2000, a survey of COI sequence variation across ten populations of the medically-important pomatiopsid Oncomelania hupensis sampled from SE Asia, ten individuals per population [4].  The maximum sequence divergence recorded in the Wilke study was a not-insubstantial 2.2%.  Here in North America, the largest study of intraspecific mtDNA sequence variation for any hydrobioid published to date was that of Hershler and colleagues [5], involving 12 Idaho populations of Taylorconcha serpenticola, 5 individuals per population.

[4] Wilke, T., G.M. Davis, C-E. Chen, X-N. Zhou, X.P. Zhang, Y. Zhang & C.M. Spolsky (2000) Oncomelania hupensis (Gastropoda: Rissooidea) in eastern China: molecular phylogeny, population structure, and ecology. Acta Tropica 77: 215-227.

[5]  Hershler, R., H-P. Liu, T.J. Frest, E.J. Johannes & W.H. Clark (2006) Genetic structure of the Western North American aquatic gastropod genus Taylorconcha and description of a second species. Journal of Molluscan Studies 72: 167-177.

[6] For more about the lost malacofauna of Oneida Lake, see:

  • Harman, W. N. & J. L. Forney (1970) Fifty years of change in the molluscan fauna of Oneida Lake, New York.  Limnology and Oceanography 15: 454 – 460.
  • Dillon, R. T., Jr. (1981)  Patterns in the morphology and distribution of gastropods in Oneida Lake, NY, detected using computer-generated null hypotheses.  American Naturalist 118: 83 – 101.

[7] Whelan, N.V. & E. E. Strong (2016)  Morphology, molecules and taxonomy: extreme incongruence in pleurocerids (Gastropoda, Cerithiodea, Pleuroceridae). Zoologica Scripta 45: 62 – 87.  With subscription: [html]

[8] Dillon, R. T., Jr. & R. C. Frankis. (2004)  High levels of DNA sequence divergence in isolated populations of the freshwater snail, Goniobasis.  American Malacological Bulletin 19: 69 - 77.  [PDF].

[9]  Dillon, R. T., Jr. & 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].  For a personal perspective, see:

  • The snails the dinosaurs saw [16Mar09]

Monday, July 6, 2020

The Return of Captain Lyon

“One man only remained behind.  It was Captain Sidney S. Lyon, of Jeffersonville, one of Indiana’s most gifted engineers.  As the Federal army moved away, he sat down upon a rock and waited.  Beside him lay a black, snake-like rope, the end running into the steep side of the mountain.  It was a fuse.  He had mined the mountain and filled the hollow with all the powder the fleeing army could spare…The tramp of the marching died away; the commissary stores were burning, and still he sat, as the night fell over the heights and the darkness filled the ravines.  Were the Confederates coming?  He heard the faint hoof-beats, the rumble of a great force of men coming from the Tennessee side.  There was the sparkle of a match, the splutter of powder, and a man fleeing down the mountain toward Kentucky for his life, and then…”
I honestly don’t know to what extent The Blowing of Cumberland Gap is true [1], but it does not matter, because it’s a great story, and I would recommend that you look up the Lyon family history [2] from google books and read pp 185 – 192, if you want to know how it turned out.  Or, if you would rather read my tenth (and final!) essay on the shell morphological variation and taxonomic confusion in the pleurocerid snails of the Tennessee/Cumberland in twelve months, soldier on below.
Sidney Smith Lyon (1808 - 1872)

In the fall and winter of 2016, a duller 154 years later, I spent a couple weeks in Frankfort, Kentucky, working with our good friend and colleague Ryan Evans on the freshwater gastropods of the Bluegrass State.  I had been surveying the region in preparation for the roll out of our new FWGO web resource for several years and, at that juncture, fancied myself familiar with most elements of the freshwater gastropod fauna of the Ohio River basin.  But what I found in KYDOW macrobenthic samples from little tributaries of the Green River, and even in some little creeks draining directly into The Ohio in western Kentucky, surprised me.  To the point that I can still remember it four years later.  Which at my age, is saying a lot.

I was already aware that P. simplex populations, of diverse shell morphology, extended across the entire drainage of the Tennessee/Cumberland from SW Virginia to Chattanooga, west through Tennessee and north into the Ohio River tributaries of Kentucky.  But my goodness!  Crawling around together with the P. simplex in the little creeks of western Kentucky, way out beyond Louisville, the KYDOW teams were also collecting pleurocerids indistinguishable to my eyes from Pleurocera troostiana, or arachnoidea, or spinella, or strigosa, or striatula, or whatever else people have called that pleurocerid bearing light, slender, striate shell with small body whorls in upper Tennessee River tributaries for almost 200 years.  The entire malacofauna of little creeks in Western Kentucky was indistinguishable from that of East Tennessee.

The shells of the particular population I was examining that afternoon were not costate, although several nearby populations were.  That is what especially struck me about those KYDOW samples, as I sat at the lab bench in Frankfort back in 2016, in addition to all the above.  I was as stricken by what I was not seeing, as what I was.  And this thought suddenly dawned on me.  If a pleurocerid species bearing a fat-smooth shell, like P. simplex, ranges through little creeks across four states, why can’t a pleurocerid species bearing a skinny-striate shell, like P. troostiana?

Western Kentucky or East Tennessee?
Let me back up for a bit of context.  Throughout Kentucky, and indeed through Middle Tennessee as well, streams of all sizes and descriptions are often choked with large and morphologically diverse populations of Pleurocera laqueata (Say 1829).  They bear shells with large body whorls that are sometimes striate but always, always costate.  I’d been looking a bottles-full of Pleurocera laqueata from central Kentucky all week.  Is it possible that some of those samples might be P. troostiana, slightly costate, not P. laqueata, slightly striate?

Have P. laqueata and P. troostiana been confounded in this part of the world for 200 years?  Might the nineteenth-century literature contain dozens of names for both, subsequently scrambled by synonymy?  If so, what are workers calling the tall-skinny-striate pleurocerids in Kentucky today [3]?

Following Branson’s [5] “Keys to the aquatic Gastropoda known from Kentucky” one finds four Goniobasis species “with longitudinal plicae” (i.e. striations) at any point in their shell growth: laqueata (Say 1829), curreyana (Lea 1841), costifera (Hald. 1841), and plicata-striata (Wetherby 1876).  The type shells borne by all four of these species are primarily costate, and I think the last three nomina will prove junior synonyms of Say’s laqueata.  Bookmark that question.  One day we’ll come back to it.

Reference to the primary literature, however, returns an excellent paper by Bickel [6] on the biology of pleurocerid populations he called “Goniobasis curreyana lyoni (Lea 1863)”.  I think that’s it.

Goniobasis lyoni then [9] and now.
Isaac Lea published a brief, Latinate description of Goniobasis lyonii – note two eyes in the original spelling [7] – in his ANSP Proceedings paper [8] “ordered to be published” on May 27, 1862 (although it says 1863 on the title page), followed by a more complete English description and figure in his ANSP Journal paper [9] “ordered to be published” on May 26, 1863.  We have touched on this pair of publications several times in recent months, featuring them in May.

Lea’s acknowledgement in the ANSP Journal paper [9] was: “I dedicate this with great pleasure to Mr. Lyon, Civil Engineer and State Geologist.”  War had not yet broken out between the states at the date of Lea’s writing, and Mr. S. S. Lyon had served as the topographer for the first (1854 – 57) Kentucky Geological Survey.

But war did come, carrying all American topographers along with it.  And my loyal readership will remember that it was Capt. Sidney Smith Lyon who stooped to capture two populations of rebel pleurocerids at Cumberland Gap in the summer of 1862, which he posted back behind the lines to Isaac Lea in Philadelphia.  Lea described that sample under four names in the smaller PANSP paper of 1863 [10] that kicked off this entire series of blog posts, way back in August of 2019.

I counted 20 hits to S. S. Lyon in Isaac Lea’s bibliography [11], first as Mr. Lyon, then as Capt. Lyon, and ultimately as Maj. Lyon, after August of 1863.  According to the family history published in 1907 [2], Lyon was an artist, a crinoid paleontologist, a naturalist, and singlehandedly saved the army of General George Morgan when it was surrounded at Cumberland Gap in September of 1862.  The account extracted at the top of the present essay was written by one Col. James Keigwin, and lovingly passed down to us by the Lyon family.

But back to the snails.  Lea’s description of Goniobasis lyonii noted that the shell was “very much drawn out” and “striate above.”  He did not mention costae but his figure (#156, reproduced above) shows light costation as well as light striation on the slender shell.  Lea gave the habitat as “Grayson County, Kentucky, S. S. Lyon.”  Its subsequent taxonomic history is Byzantine [13], but it was the substance of Bickel’s 1968 paper that lyonii should be resurrected as a subspecies of curreyana, which I don’t think it is [14], but I do give thanks for the resurrection.

Bickel restricted the lyonii type locality to Spring Fork Creek, a tributary of the Rough River in Grayson County, Kentucky.  He also reported populations in seven other small streams in four other counties: Breckinridge, Meade, Hardin, and Larue.  I sampled Spring Fork at three locations on the morning of 15May19 and was most disappointed by the quality of the environment, which in the last 50 years has declined to the status of muddy ditch, and by the population of pleurocerids dwelling therein, which has dwindled to zero.  Providentially, my database contained three other Grayson County sites at which lyonii populations had been collected by the KYDOW, and I found a decent population in a tributary of Big Run Branch, 5 km W of Leitchfield (37.5029, -86.3411).  See the example figured above.

Attributed to S. S. Lyon [12]
Pleurocerid populations bearing slender shells of the lyonii phenotype are not uncommon in small tributaries of the Tennessee, Cumberland, Green and Ohio Rivers in Kentucky west of Louisville and in Tennessee west of Nashville.  I cannot find any argument counter to the suggestion that lyonii (Lea 1862) is a junior synonym of troostiana (Lea 1838).  But let’s continue to recognize this set of populations with a subspecific nomen, Pleurocera troostiana lyonii, shall we?  And again, please review the definition of the word “subspecies” as adopted by the FWGNA from footnote [16] below.

Some populations of P. troostiana lyonii bear shells with light costation around their apex, rendering them effectively indistinguishable from P. troostiana perstriata, and some do not, rendering them indistinguishable from P. troostiana troostiana.  I struggled with the suggestion offered above.  Ultimately, I decided to preserve the S. S. Lyon patronymic in the pleurocerid canon more to protect the small (but not insignificant) literature associated with the taxon than to further any grand evolutionary hypothesis.  Besides which, I have grown rather fond of the gentleman.  He was not some pompous jackass sitting high-and-mighty behind a walnut desk in Philadelphia.  Capt. Sidney Smith Lyon did his duty.

Now at last, the time to summarize has arrived, woohoo.  Available from the link below is a pdf download entitled:


Here I have listed and figured all 13 of the specific and subspecific nomina I have synonymized under Isaac Lea’s Pleurocera troostiana since last August, together with type (or typical) localities and references.  I have not listed all the dozens of older synonyms under these nomina, as catalogued by Tryon and Goodrich. Quoting the latter, “I have not had the heart.”  This is FWGNA Circular Number 2 (July 6, 2020).


Notes:

[1] Or maybe they’re lyon?  Sorry, I couldn’t resist.

[2] Lyon, S.E., et al. (1907) Lyon Memorial: Families of Connecticut and New Jersey, including records of the descendants of the immigrants Richard Lyon of Fairfield and Henry Lyon of Fairfield.  Detroit: William Granham Printing.  Pp 185 – 192.

[3] Back in November we reported that Isaac Lea described 505 species of pleurocerids.  Well, Dan Graf [4] cataloged approximately 500 more, contributed by other authors.  Those 1,005 names are a slough of despond into which I do not intend to fall.  So my approach for 40 years has been first to work out the biology, and then to work out the taxonomy.  First, my evolutionary intuition suggests that there are approximately 40 biological species of pleurocerids in North American waters, with another 20 subspecific nomina that may prove of some utility.  So second, I am trying to figure out what 60 names to call those populations or groups of populations.  Those 60 names may not be the oldest, nor the most familiar; they may be a compromise between age and modern use.  But if I live to be 107, I will never get to task #3, what the heck most of those other 945 names mean.

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

[5] Branson, B.A. (1987)  Keys to the aquatic Gastropoda known from Kentucky.  Trans. Kentucky Acad. Sci. 48: 11 - 19.

[6] Bickel, D.  (1968)  Goniobasis curreyana lyoni, a pleurocerid snail of west-central Kentucky. The Nautilus 82: 13 - 18.

[7] To quote The Eagles, “You can’t hide your lyon eyes,” pleural.  OK, I’ve got all the corny jokes out of my system, for now.

[8] Lea, Isaac. (1862) Description of a new genus (Goniobasis) of the Family Melanidae and eighty-two new species. Proc. Acad. Nat. Sci., Phila., xiv, pp. 262-272.

[9] Lea, Isaac (1863) New Melanidae of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 217 – 356.

[10] Lea, Isaac (1863) Descriptions of fourteen new species of Melanidae and one Paludina.  Proceedings of the Academy of Natural Sciences of Philadelphia 15: 154 – 156.

[11] Scudder, N. P. (1885)  Bibliographies of American naturalists – II. The published writings of Isaac Lea, LL.D.  Bull. US National Museum 23: 1 – 278.

[12] For more about the “White Horse” painting attributed to S. S. Lyon, see:
Clark County Museum looking for help to restore historic painting.  News and Tribune (Clark County, Indiana).  February 12, 2018. [html]

[13] I quote Bickel [6] verbatim: “This animal is Goniobasis lyoni Lea, 1863, a species that Tryon (1865) placed in the synonymy of Goniobasis glauca (Anthony).  It was subsequently transferred along with G. glauca to the synonymy of Goniobasis athleta (Anthony) by Tryon (1873), and Goodrich (1940) shifted it to the synonymy of Goniobasis laqueata (Say).  Goniobasis lyoni is a form of Goniobasis curreyana (Lea) and is distinct enough to merit recognition.”

[14] It is hard for me to understand why Dave Bickel thought lyonii was a subspecies of curreyana.  Lea’s (1843) figure clearly depicts Melania curryana as a laqueata-type, bearing an aperture “about one-third the length of the shell,” not a troostiana-type, with aperture smaller.  And Lea specifically stipulated [15] that the shell of curreyana “is without striae,” focusing instead on the “large and strong folds.”  Lea’s (1841) Melania curreyana is clearly a junior synonym of laqueata (Say 1829) and has nothing to do with his Goniobasis lyonii of 1862.

[15] Lea, Isaac (1843)  Description of New Fresh Water and Land Shells.  Transactions of the American Philosophical Society 8: 163 – 250.

[16] Subspecies are populations of the same species in different geographic locations, with one or more distinguishing traits.  For elaboration, see:
  • What is a subspecies? [4Feb14]
  • What subspecies are not [5Mar14]

Friday, June 5, 2020

What is Melania edgariana?


If you follow the FWGNA blog on a regular basis, bless your heart, it is possible, indeed likely, that a terrible revelation has by now dawned upon you.  You have become ensnared in a series of essays on shell morphological variation in the pleurocerid fauna of the Tennessee/Cumberland that began back in August of 2019, eight episodes ago, with no end in sight.

And even as this soggy mat of dubious science, arcane history, and overwrought pontification has unrolled these many months, the supercilious weaver who labors today to augment its warp and weft expects you to remember threads now gone, and appreciate patterns as yet emerging. 

But he will deign to refresh your memory, briefly.  In August we heard the story of Captain S. S. Lyon, who in 1862 sent a sample of pleurocerid snails collected from Cumberland Gap to the eminent scientist Dr. Isaac Lea in Philadelphia.  Although Lea gave four new names to this collection of snails, the evidence available to us today suggests that only two species were actually present, best identified as Pleurocera simplex (Say 1825) and P. troostiana (Lea 1838).  And in Gap Creek, at least, their shell morphology seemed to vary together.  Both populations were dwarfed upstream and typical downstream, demonstrating the phenomenon we abbreviate CPP, for “cryptic phenotypic plasticity,”

In September and October, we learned that populations of P. simplex range throughout Tennessee and Kentucky, varying strikingly in their shell morphology, likely as a consequence of CPP.   And in December, January, April and May, we documented a similar but even more extreme phenomenon in populations of Pleurocera troostiana, inhabiting a big swath of the Tennessee drainage from SW Virginia through East Tennessee into North Alabama. Everywhere in this vast region we have seen simplex and troostiana living side-by-side, varying together.

Melania edgariana [1]
Now the main theme of our September post was this.  In the Cumberland River drainages of Middle Tennessee and Kentucky, populations of Pleurocera simplex inhabit larger rivers than they do in the Tennessee River drainages further east.  And correlated with this range extension, they bear shells that are larger, broader, and heavier than the P. simplex populations of East Tennessee drainages.  The middle Tennessee populations are so different from populations of East Tennessee that they have traditionally been identified by a different specific nomen, ebenum (Lea, 1841), and in some cases even a different genus, Lithasia.

Might the range of P. troostiana also extend through the Cumberland drainages of Middle Tennessee into Kentucky as well?  Perhaps shifting shell morphology in parallel with P. simplex, demonstrating similar levels of CPP?

Yes.  In 1841 Isaac Lea published a brief, Latinate description of “Melania edgariana,” with full description and figure in 1843, sent to him from “Cany Fork, Tenn.” by Mr. S. M. Edgar [1].  This must be a misspelling of Caney Fork, the tributary of the Cumberland River from which we extracted the Pleurocera simplex populations we studied in September.   Lea described the shell of edgariana as “spire elevated,” and enthused “it is remarkable for being folded and transversely striate on all the whorls.”

In 1873 G. W. Tryon [2] synonymized edgariana under Goniobasis nassula, which T. A. Conrad had described from the Big Spring at Tuscumbia, Alabama, in 1834 [3].  Tryon said, and I quote verbatim: “Mr. Lea agrees with me that his Edgariana is a synonym of nassula.”  Lea despised Conrad [4].  Wouldn’t you have loved to be a fly on the wall when Lea and Tryon had their conversation about edgariana?

Goodrich disagreed with Tryon, however, removing Goniobasis edgariana from under the synonymy of Conrad’s G. nassula, suggesting for the range of edgariana “Streams of Cumberland, Duck and Elk Rivers, Tennessee” and listing 13 synonyms underneath it [5].

And as usual, I’m with Goodrich.  I really think that the population of pleurocerids inhabiting Tuscumbia’s Big Spring is something else.  The biological situation at Tuscumbia’s Big Spring is even more fascinating than the situation at Huntsville’s Big Spring, and I feel sure we will come back to Tuscumbia in some future post.  But for now, we will stipulate that Lea’s edgariana and Conrad’s nassula are two entirely different things, and that’s all I’ve got to say about that.

So back to the Caney/Collins River system.  It will be remembered from our September post that populations of Pleurocera simplex become progressively more robust and heavily-shelled from headwater tributaries on the west slope of the Cumberland Plateau north toward the confluence of the Caney with the Cumberland River at Carthage, TN.  I’ve taken a slice from the map I published in September and expanded it below, retaining simplex sites J, K, and L.  

(J) Collins River, (I) Center Hill Lake, (H) Caney Fork
The cryptic phenotypic plasticity demonstrated by populations of P. simplex in the Caney/Collins is especially important for the argument I’m preparing to advance below.  So if my September post is not vivid in your memory, I’d be gratified if you opened this link [4Sept19] in a separate window and reviewed the material featured therein.  We will wait for you.

Are you back?  Good.  Going forward now.

Crawling around on the rocks with P. simplex in the Collins River at site J (35.5874, -85.6994) is a population of pleurocerids bearing shells with elevated spires, folded and transversely striate, as depicted at far left in the figure below.

This must be Isaac Lea’s Melania edgariana.  The snails bearing shells such as depicted in figure (J) below are occupying the same habitat as topotypic troostiana in East Tennessee, and all of those troostiana synonyms we reviewed in January, and topotypic perstriata in North Alabama, and all of those perstriata synonyms we reviewed in May.  In the company of P. simplex, they are grazing on the rocks of a small stream coursing down off the Cumberland Plateau.

There are two differences between edgariana of the Cumberland drainage and troostiana of the Tennessee drainage.  One is that, just as is the case with simplex, the edgariana populations of the Caney/Collins system extend much further downstream than the troostiana of East Tennessee and North Alabama.  My biological intuition suggests to me that a combination of current speed, substrate, temperature, and oxygenation is involved, such that the Caney/Collins, and many other rivers of Middle Tennessee and Kentucky, retain more of their upstream character downstream.  They look like big trout streams, not bass rivers.

In response to common environmental conditions, the shell morphology demonstrated by freshwater gastropod populations may vary together.  One of the more interesting papers to pass across my desk in recent years reports a shell morphological study conducted by Kistner and Dybdahl [6] in the Snake River of Idaho [7].  The authors demonstrated that generalized Procrustes variance in populations of the (native) Pyrgulopsis robusta and the (introduced) Potamypyrgus antipodarium varied in parallel, apparently as a function of current speed.

(J) Collins R, (I) Center Hill Lake, (H) Caney Fork
So the only other distinction between the edgariana of the Cumberland drainage and the troostiana of the Tennessee is the degree of shell costation – strong for edgariana, weak for subspecies perstriata in North Alabama, and absent for the typical subspecies in East Tennessee.  We devoted some considerable fraction of our April post to research on shell costation or plication.  Intraspecific variation in that trait has been well-documented – sometimes apparently heritable, sometimes not – but intraspecific, in any case. 

I cannot find any evidence counter to the hypothesis that Melania edgariana (Lea 1841) of the Cumberland is a junior synonym of M. troostiana (Lea 1838) of the Tennessee.  But let us save Lea’s name “edgariana” as a subspecies to describe populations of P. troostiana bearing strongly costate shells, shall we?  Again, I am duty-bound to remind my readership that we here in the FWGNA project define the term “subspecies” in its original, classical sense, and to point you to my essays of February and March, 2014, for elaboration [8].

I do not want to nominate the population of edgariana at site J as topotypic, however, since it inhabits the Collins River, and Lea specified “Cany” Fork.  So further downstream, in 1948 the US Army Corps of Engineers built Center Hill Dam near Smithville, and impounded the Caney Fork upstream 64 miles, almost to its junction with the Collins River.  Most unexpectedly, to me in any case, several pleurocerid populations, including edgariana, have survived the impoundment [9].  The shell labelled (I) in the figure above was collected during the winter draw-down from a population inhabiting the sandy shallows of Center Hill Lake at the Floating Mill Recreation Area (36.0460, -85.7620).

But again, I hate to restrict an 1841 type locality to a 1948 impoundment.  So the Caney Fork picks up again below the Center Hill Dam and flows another 25 miles to its mouth at The Cumberland River.  The shell labelled (H) in the figure above was sampled at the TN 264 bridge (36.1816, -85.9081), a spot I suggest as the type locality for Pleurocera troostiana edgariana by virtue of ease of access, as well as historical fidelity.

As Goodrich [5] suggested, Pleurocera troostiana edgariana populations seem to range widely across the Cumberland drainage of TN/KY, including the Stones, Harpeth, and Obey Rivers as well as the Caney/Collins.  And indeed, several of the larger tributaries of the Tennessee River in Middle Tennessee also host edgariana populations, including the Duck [10] and the Elk.  We depicted a specimen from the Elk River at Kelso (site “G”) last month, as a teaser for this month’s essay.

Well, I do appreciate the forbearance of my rapidly-dwindling readership as yet another soggy length of malacological tapestry has rolled off the FWGNA loom, dripping with arcana and arrogance.  Next month we’ll finish up where we started, back in Kentucky with Captain Lyon, and summarize, at long last, I promise.


Notes:

[1] These were the same publications in which Lea described the M. ebenum about which we obsessed in October, and the M. teres and M. strigosa we mentioned in January:
  • Lea, Isaac (1841) Continuation of Mr. Lea's paper on New Fresh Water and Land Shells.  Proceedings o the American Philosophical Society 2: 11 – 15.
  • Lea, Isaac (1843)  Description of New Fresh Water and Land Shells.  Transactions of the American Philosophical Society 8: 163 – 250.
[2] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

[3] Conrad, T.A. (1834)  New fresh water shells of the United States, with coloured illustrations, and a monograph of the genus Anculotus of Say.  Also a synopsis of the American naiades.  Judah Dobson, Philadelphia.  76 pp.

[4] For all we know about the Lea/Conrad relationship, see:
  • Isaac Lea Drives Me Nuts [5Nov19]
[5] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[6] Kistner, E.J., and M.F. Dybdahl.  2014.  Parallel variation among populations in the shell morphology between sympatric native and invasive aquatic snails.  Biological Invasions  16(12):2615-2626.

[7] We devoted a significant number of column inches to the Pyrgulopsis robusta populations of the Snake River some years ago.  See:
  • Idaho Springsnail Showdown [28Apr05]
  • Idaho Springsnail Panel Report [23Dec05]
  • When pigs fly in Idaho [30Jan06]
  • FWS Finding on the Idaho Springsnail [4Oct06]
[8] Subspecies are populations of the same species in different geographic locations, with one or more distinguishing traits.  For elaboration, see:
[9]  In addition to P. troostiana edgariana, the pleurocerid species inhabiting the margins of Center Hill Reservoir include P. canaliculata, which does not surprise me, and P.laqueata alveare, which is really rather interesting.  But no, I have not seen any P. simplex in the shallows of Center Hill Lake.  Why not?  We may come back to this.

[10] According to van der Schalie (Sterkiana 52: 45 - 56), in 1931 Goodrich recorded Goniobasis edgariana way up the Duck River at Manchester.  He did not apparently find edgariana, or any pleurocerid populations that looked anything like troostiana, anywhere else in the Duck drainage.  But I am  not sure how well Goodrich surveyed the smaller tributaries.

Sunday, May 10, 2020

A House Divided

Editor’s Note – This the eighth essay in a seemingly-endless series on phenotypic variety and taxonomic confusion in the pleurocerids of the Tennessee/Cumberland.  To appreciate the arguments advanced below, you really must have read last month’s post, and it would help to have read December and January as well.

By the spring of 1862, America had reached a point of crisis.  Isaac Lea had run out of names for pleurocerid snails.

Between 1834 and 1861 Lea had described 184 species in the genus Melania, which he now wrote had become “so enormously extended as almost to prevent the possibility of finding suitable names for its species.”  So in April of 1862 Lea [1] proposed to split a large subset of Melania bearing shells with “auger-shaped” apertures into a new genus Trypanostoma.  And in May [2] he proposed to split another large subset bearing shells with “subrhomboidal” apertures into a second new genus, Goniobasis.

Lea then went on to describe 242 new pleurocerid species in 18 months, as though the pressure in some vast balloon of Latinate adjectives had suddenly been exploded by nomenclatorial pin prick.  The splatter included spinella which we reviewed in January [3] and the aterina / porrecta / vittatella / cumberlandensis clot we featured way back in August [3], sent to Lea by Captain Lyon from way down yonder in Cumberland Gap.  Also detonated onto the pages of learned journals in 1862/63 were a tremendous variety of additional nomina assigned to pleurocerid populations from throughout the Tennessee/Cumberland region, including Goniobasis gabbiana, which immediately arced into oblivion, only to be called back on this blog in 2016 [4].


Lea’s genus Trypanostoma never caught on.  George Tryon [5] considered it “unquestionably” a junior synonym of Rafinesque’s Pleurocera [6], as did Goodrich [7] and Burch [8].  But Lea’s genus Goniobasis was accepted by both Tryon and Goodrich as describing a “natural” group, hanging on until the 1980s, when Burch resurrected the zombie taxon, Elimia, to replace it.

We now understand, of course, that the distinction made by Lea in 1862 was illusory.  There is no  evolutionary difference between Trypanostoma, Pleurocera, Goniobasis or Elimia whatsoever [9].  The tragic rift that tore the pleurocerid fauna apart in 1862, setting brother against brother, would not be healed for 150 years.

Nevertheless, in 1873 George Tryon, almost certainly in direct consultation with Isaac Lea himself, divided all 184 species that Lea had described prior to the Trypanostoma/Goniobasis crisis of 1862 into either Pleurocera or Goniobasis.  In general, the larger and more heavily-shelled nomina went into the former genus and the more lightly-shelled species into the latter.  During that process, all five of the previously-described slender, striate East Tennessee species we discussed in January [3] were allocated to Goniobasis: troostiana (Lea, 1838), teres (Lea, 1841), strigosa (Lea, 1841), striatula (Lea 1841) and arachnoidea (Anthony 1854).  As well as the perstriata Lea described from North Alabama in 1852. 

So last month we reviewed the situation with Melania (now Goniobasis) perstriata, suggesting that the Huntsville-area populations described by Lea using that particular sobriquet might best be understood as a plicate subspecies of the troostiana population he described from East Tennessee way back in 1838.  We also hinted that quite a few additional names for similar populations inhabiting similar waters of North Alabama might have been described in the aftermath of  the 1862 unpleasantness [10].  Among these were pybasii (1862), paupercula (1862), crispa (1862) and decampii (1863).

Pleurocera troostiana populations, Note [22] and map below.

Lea led his 1863 description of Goniobasis pybasii [11] with “shell folded, very much drawn out,” and went to unusual lengths comparing it to four other species previously described: “reminds one of laqueata (Say),” “allied to deshaysiana but more slender [12],” “very much like grata (Anthony) [13],” and “differs from lyonii by not being striate [14].”  He did not distinguish pybasii from perstriata, nor indeed from any of his East Tennessee species, troostiana or any of the synonyms we reviewed in January.  Lea gave the habitat of Goniobasis pybasii as “Tuscumbia, Alabama, B. Pybas [15].”

Tryon [5] passed pybasii along verbatim.  Goodrich opened his 1930 treatment of G. pybasii [17] with the observation that “this species does not seem to have been collected in recent years.”  He did, however, examine nine shells (bearing poor data) then held by the Alabama museum, writing “The chief characteristic of the species is that, unlike the other plicate Goniobases of the region, it lacks the granulate spire and the usual revolving raised lines.”  He went on to broaden its range to “springs and streams of North Alabama.”  Burch [8] passed Elimia pybasii along on his page 140, unfigured.

So on March 12, after my tour of lovely Madison County, Alabama, I struck out across the rolling hills and lush farmlands toward Tuscumbia, the home of Hellen Keller, Annie Sullivan, and the first railroad on the American frontier [18].  And over the course of several days following, I was able to inventory, lightly but completely, the freshwater gastropod fauna inhabiting the springs and small streams of North Alabama.

And it materializes that pleurocerid populations bearing “shells folded, very much drawn out” that match Lea’s figure of 1863 are today widespread in the springs and small streams south of Tuscumbia.  And as a type locality for Goniobasis pybasii, I hasten to nominate what may be my favorite freshwater gastropod sampling site ever, the small spring and spring run at the foot of the Rattlesnake Saloon (Q).

My favorite sampling site, ever.

By great good fortune, the hour was getting on toward quitting time on a Wednesday evening when I pulled my pickup into the ample parking lot of the Rattlesnake Saloon, about 2 miles south of Tuscumbia.  The public establishment is located a brief stroll through verdant pastureland and a steep descent under a massive rock overhang about 20 – 30 yards above Newsom Springs.  Beer and pleurocerids on a warm Alabama evening in mid-March?  I cannot remember ever enjoying anything I have called “work” more than this.  See the example shell marked (Q) above.

Lea described Goniobasis paupercula [11] in the same 1863 article as pybasii, 11 pages later, giving the habitat simply as “North Alabama, Prof. Tuomey [19].”  His description of the “subcylindrical” shell mentions whorls “folded above and striate at the apex.” But in his remarks, he confessed that he had “not a single one with an entirely perfect apex, being usually decollate at the second whorl from the base.”  In contrast to pybasii, Lea did not compare paupercula to any other pleurocerid previously described – not to perstriata or anything else – implying, I suppose, that something in his description made paupercula self-evidently unique.  Possibly the decollation?  In any case, Tryon passed paupercula along uncritically.

Goodrich (1930) reported observations on seven populations of paupercula collected by H. H. Smith from small streams in Lauderdale and Franklin Counties, Alabama.  Goodrich’s notes on shell morphology expanded those of Lea considerably, especially with respect to variation in shell sculpture.  Burch [8] picked up the species from Goodrich (1940) and passed it along (with Tryon’s redraft of Lea’s original figure) on his page 140, giving the range simply as “creeks of Northern Alabama.”
Juvenile, 9.2 mm

My surveys through Lauderdale and Franklin Counties this March did not yield any pleurocerid populations bearing decollate shells.  But I did stumble upon a population bearing shells very nearly identical to Lea’s 1863 description and figure in Lipscomb Spring, south of Huntsville, on the opposite side of the Tennessee River (R).  The figure above shows an adult shell, the figure at left a juvenile, suggesting that Lea’s speculation about striae around the apex was correct.

Lea published a brief, Latinate description of Goniobasis decampii in 1863, which he followed with a more complete English description in 1866 [20].  The shell, he reported, was “plicate, striate below, greatly attenuated, thin.”  Lea gave the habitat as “Huntsville, Alabama; Wm. H. DeCamp, MD, surgeon United States Army [21].”

To quote Goodrich (1930) verbatim: 
“This mollusk is G. perstriata in all essentials save its nearly cylindrical shape.  Quite slender specimens of perstriata have been taken in Big Spring Creek at Huntsville… It is possible that the original collector, Dr. DeCamp, had visited some spring or creek in the vicinity of Huntsville containing these shells, and that the locality has not since been examined.  A ‘pure culture’ of decampii would warrant, of  course, its definite recognition.”
In my week of sampling springs and streams around North Alabama I did not find a single individual pleurocerid bearing a shell as “greatly attenuated, thin” as Lea’s figure suggests, much less a “pure  culture.”  Goodrich’s speculation seems quite plausible to me – that the single shell sent Lea by Dr. DeCamp was subsampled from the perstriata population of Big Spring, Huntsville, subsequently much impacted by development.

The biological and morphological considerations reviewed above combine to suggest to me that all three of these nominal species, pybasii (Lea 1862), paupercula (Lea 1862), and decampii (Lea 1863), are junior synonyms of Pleurocera troostiana perstriata (Lea 1853).  All three of these nineteenth-century taxa were defined entirely by their shell morphology.  And the shell morphology demonstrated by the example populations we have identified this month rests easily within the variance of the Huntsville-area P. troostiana perstriata populations we documented last month.

North Alabama.  See footnote [22] for locality data.

But regarding crispa (Lea 1862).  Lea described Goniobasis crispa from “Florence, Alabama; Rev. G. White” in the same 1863 paper as pybasii and paupercula, two pages after the latter [11].  Goodrich neglected it in his 1930 work but brought crispa back as a subspecies of Goniobasis perstriata in 1940 [7].  No, Goniobasis crispa is not a subspecies of perstriata, nor is it a synonym of troostiana, nor is it related to any other species we have treated this month, or at any time in recent memory.  Goniobasis crispa (Lea 1862) is entirely different.  And to quote my favorite Alabaman, “That’s all I’ve got to say about that.”

But I will say two more things about two other gastropod populations and close with one rhetorical question.  The first thing I will say is that the tributaries of the Elk River in North Alabama are inhabited by pleurocerids bearing slender, lightly-costate shells no different from any of the other Pleurocera troostiana perstriata populations we have reviewed in the last couple months.  See the example shell from Mechanic Branch at Sim Corder Mill (S) figured way up above.

And the second thing is that if one samples up the main Elk River just a short way into Tennessee, one begins to discover populations of pleurocerids bearing slender, high-spired shells elaborately ornamented with both strong striae and dramatic costae down the entire length of their shells, from apex to lip. See the example from the Elk River at Kelso (G) above.

What is the situation with Pleurocera troostiana in Middle Tennessee?  Stay tuned.

Notes:

[1] Lea, Isaac. (1862) Description of a New Genus (Trypanostoma), of the Family Melanidae, and of forty-five New Species. Proc. Acad. Sci., Phila., xiv, pp. 161 - 175.

[2] Lea, Isaac. (1862) Description of a new genus (Goniobasis) of the Family Melanidae and eighty-two new species. Proc. Acad. Nat. Sci., Phila., xiv, pp. 262-272.

[3] Here’s my entire series on Pleurocera troostiana:
  • CPP Diary: Yankees at The Gap [4Aug19]
  • On the trail of Professor Troost [6Dec19]
  • The many faces of Professor Troost [7Jan20]
  • Huntsville Hunt [15Apr20]
[4] The most convenient medium by which to review the rediscovery of Pleurocera gabbiana would be to read essays 9 - 11 in:  Dillon, R.T., Jr. (2019c) Essays on The Prosobranchs.  Freshwater Gastropods of North America, Volume 3.  FWGNA Press [html].  Or, if you’d prefer to click your way through it piecemeal:
  • The cryptic Pleurocera of Maryville [13Sept16]
  • The fat simplex of Maryville matches type [14Oct16]
  • One Goodrich missed: the skinny simplex of Maryville is Pleurocera gabbiana [14Nov16]
[5] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

[6] Tryon turned out to be quite wrong here.  The question of whether Lea’s Trypanostoma might indeed be a junior synonym of Rafinesque’s Pleurocera was swept up into one of the longest-running feuds in American Malacology.  See:
  • Joe Morrison and the Great Pleurocera Controversy [10Nov10]
[7] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[8] 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).

[9] 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].  For more, see:
  • Goodbye Goniobasis, Farewell Elimia [23Mar11]
[10] Isaac Lea described several more heavily-shelled species of pleurocerid snails from North Alabama bearing elevated spires and sometimes even striations that were ultimately allocated to Trypanostoma/Pleurocera.  Among these were brumbyi (1852), striatum (1862) and currieranum (1863).  Goodrich [5] synonymized striatum (from “Florence, Alabama B. Pybas”) under canaliculata.  And it is my hypothesis that the “spring in Madison County” from which Goodrich identified the brumbyi/currierianum pair is Brahan Spring in Huntsville (34.7062, -86.6003), in which case, that pair of specific nomina appear to be junior synonyms of Pleurocera canaliculata as well, subspecies pyrenellum.


[11] Lea described paupercula, pybasii and crispa in brief, Latinate form in his 1862 PANSP paper cited at note [2].  They were figured and described more completely in English the next year, in:
Lea, Isaac (1863) New Melanidae of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 217 – 356.

[12] Lea’s deshaysiana of 1841/42 (habitat “Tennessee”) was synonymized under laqueata (Say1829) by Goodrich [7, 16].

[13] Anthony’s 1860 grata (habitat: “Alabama”) has been buried by the sands of time.  Rest in peace.

[14] Put a bookmark here.  We will return to the Goniobasis lyonii populations of Kentucky in a couple months.

[15] In the original (10May20) version of this blog post, I footnoted here, "About the life of Mr. Pybas I have found nothing."  In September, however, I was pleased to receive an email from Ms. Robin Gaither, a great, great granddaughter of Benjamin Pybas, whose dates I now know to be 1808 - 1883.  Ms. Gaither shared that Grandpa Ben was a cabinet maker and coffin maker / undertaker in Tuscumbia.  Have you ever heard the Guy Lombardo standard,"Stars Fell on Alabama?"  That song was inspired by a dramatic Leonid meteor storm in November of 1833.  Grandpa Ben found a star and sent it to the Smithsonian [16].

[16] Actually, the Smithsonian wasn't founded until 1846.  I googled around and found a paper contributed to the Sheffield Laboratory of Yale College reporting a "meteoric stone" which fell 16 miles SE of Tuscumbia in 1868 being sent to Yale by Mr. Benjamin Pybas.  But I like the "Stars Fell on Alabama" story more, so that's what I'm going with. 

[17] Goodrich, C. (1930)  Goniobases of the vicinity of Muscle Shoals.  Occasional Papers of the Museum of Zoology, University of Michigan 209: 1 – 25.

[18] In 1834 local merchants completed a railroad from Decatur to Tuscumbia to bypass the 43-mile Muscle Shoals of the Tennessee River.  This line was incorporated into the Memphis & Charleston Railroad in 1850, ultimately becoming the first connection between Alabama and The East.  Cotton was, of course, the primary motivation for the construction of these commercial arteries.  The conduct of freshwater gastropods to Philadelphia was apparently an afterthought.

[19] Michael Tuomey (1805 – 1857), professor of geology at the University of Alabama, appointed first state geologist of Alabama in 1848, working out of Tuscaloosa, travelling broadly.

[20] Brief, Latinate description of Goniobasis decampii:
  • Lea, Isaac (1863) Descriptions of fourteen new species of Melanidae and one Paludina.  Proceedings of the Academy of Natural Sciences of Philadelphia 15: 154 – 156.
English description with figure:
  • 1866. Lea, Isaac.  New Unionidae, Melanidae, etc. chiefly of the United States.  Journal of the Academy of Natural Sciences of Philadelphia (New Series) 6: 113 – 187.
[21] Dr. William H. DeCamp (1825 – 1898), originally from New York, removed to Grand Rapids in 1854, served as a surgeon in the First Michigan Engineers and Mechanics Regiment 1861 – 64.  He resumed practice in Grand Rapids and was ultimately elected to the presidency of the Michigan State Medical Society.

[22] Pleurocera troostiana populations referenced in this essay:
  • Q = Newsom Springs at the Rattlesnake Saloon. 34.6481, -87.9076
  • R = Lipscomb Spring. 34.5241, -86.6013
  • S = Mechanic Branch at Sim Corder Mill.  34.9364, -87.1314
  • G = Elk River 2 km N of Kelso. 35.1395, -86.4484