Dr. Rob Dillon, Coordinator

Tuesday, March 7, 2023

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.

I sent a sample from this population (“C”) to our colleague Cindy Norton back in 2018, and her breeding experiments returned no evidence of reproductive isolation between population C and a sample of Helisoma scalare scalare (“F”) from way down in the Florida Everglades [15].  So, since the shells they bear are planispiral, the best, most modern identification for the Charles Towne Landing population C is currently Helisoma scalare duryi [16].

Charles Towne Landing SP
The only quibble one might offer to the identification of Population C as Planorbis 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 planorbid populations bearing shells of all these duryi morphologies 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.  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]

Tuesday, February 7, 2023

New Clothes for The Emperor

Editor’s Note - If you’re just joining us, I apologize.  This month’s blog builds from a series of eleven essays on the morphology, systematics, ecology and biogeography of the planorbid genus Helisoma in the southeastern United States, stretching all the way back to 2004, as listed at footnote [1] below.  No, you don’t have to read that entire list, unless you are seriously interested in the science.  But the story below won’t make any sense at all unless my two most recent essays, [6Dec22] and [5Jan23], are fresh in your mind.  Oh, and all that anatomical mishmash I reviewed two years ago, in [9Feb21] will be super helpful for this month’s essay, as well.

Both Helisoma scalare and Helisoma duryi were described in the 19th century from “The Everglades of Florida.”  Both of their type localities were, however, hundreds of miles north of the ecological region formally recognized as The Everglades here in the 21st.  And none of the 20th century monographers who reviewed the planorbid gastropods in the interim: Henry Pilsbry [2] in 1934, F. C. Baker [3] in 1945, or Bengt Hubendick [4] in 1955, had on his lab bench any live-collected topotypic material for either nominal species.  And as I merged into the eastbound lanes of I-10 on Tuesday morning Feb 23, 2021, Tallahassee in my rearview mirror, neither did I.

Both Pilsbry and Baker based their extensive and detailed redescriptions of Helisoma scalare on a population of planorbids sampled from “Lake Butler, Pinellas County.”  In 1949 the Florida legislature changed the name of that particular body of water to “Lake Tarpon” to mitigate confusion with another Lake Butler elsewhere in The Sunshine State. And so, it was the coordinates of a boat launch in the John Chestnut Park on the SE shore of Lake Tarpon, about 15 miles NW of Tampa, that I had keyed into the GPS on my dash that cloudy February morning.

Helisoma scalare from Lake Tarpon (nee Butler)

And the body of water into which I launched my kayak some four hours later, light drizzle notwithstanding, was a lovely lake of 2,500 acres, average depth 8 feet, clear and cool and blessed with an abundance of macrophytic vegetation of all sorts: floating, emergent, and submerged.  And the weeds of that last-listed category, wafting in the gentle currents at depths of an arm’s length, were laden with Helisoma scalare bearing shells of a most gratifyingly classic morphology, as depicted in the figure above.

The situation in Lake Tarpon (nee Butler) turned out to be quite reminiscent of that I described in The Everglades at the 40-Mile-Bend a couple years ago [5Oct20].  The flat-topped Helisoma seem to reach maximum abundance in the rooted-submerged macrophytes in both places, especially inside beds of eel grass (Vallisneria).  I also noted high densities around the roots of emergent vegetation, such as cat tails (Typha).  The snails do not seem to crawl up those Typha stems to the surface under any circumstance, however.  Their life habit appears exclusively benthic.

Indeed, during the couple hours I waded and kayaked around the margins of Lake Tarpon, I developed the strong impression that no element of the entire population of Helisoma dwelling therein ever, from its birth to its death, rose to enfold an air pocket under its mantle, under any circumstance.  This suggested to me that they would not adapt well to warming or artificial enrichment, or to any perturbation that might cause levels of dissolved oxygen to dip in their lovely lacustrine environment.  Helisoma scalare populations seem to need large volumes of cool, clean, clear water.

Such a situation contrasts strikingly with the typical habitat of Helisoma duryi in my experience, or (indeed) Helisoma trivolvis throughout the remainder of North America.  Populations of more typically-planispiral planorbids are ordinarily found grazing in floating macrophytes in warm, rich ponds or ditches, or on the margins of riverine backwaters, almost always near the surface.

Lake Tarpon

And back wading in Lake Tarpon, I also developed the strong impression that, setting aside their peculiar scalariform morphology, the shells borne by this particular population of pulmonate snails were exceptionally thick, heavy, and robust.  This seemed to imply some special adaptation for defense against crushing predation.  At this suggestion, the schools of bream darting about in the clear waters around my feet seemed to nod their heads in agreement.

The skies were growing leaden over the crystalline waters of Lake Tarpon as I loaded my kayak back into my pickup and pushed the button on my GPS unit for home.  And the next afternoon I dumped my big, fresh sample of H. scalare in a tray on my lab bench and pulled out the big samples of H. duryi I had collected in 2020.  And I opened my well-thumbed copy of Pilsbry 1934 on the left side of my lab bench, and my much-beloved copy of Baker 1945 on the right.  And to refresh everybody’s memory:

In 1934 “The Elderly Emperor” gathered four previously described species of Floridian planorbids into a new subgenus of Helisoma he called Seminolina: scalare (Jay 1839), duryi (Wetherby 1879), and two fossil species of Dall (1890), conanti and disstoni.  Under Helisoma (Seminolina) duryi he recognized six subspecies: the typical H. duryi duryi (Wetherby), intercalare (Pilsbry 1887), preglabratum (Marshall 1926), and three new ones: normale, eudiscus, and seminole.  Together this set of six subspecific nomina described a completely seamless progression from the compressed, tightly-planispiral eudiscus to the taller, more loosely-planispiral typical form to the flat-topped, scalariform seminole.

From Pilsbry [5]

But to be clear.  Pilsbry did not subscribe to the modern requirement that subspecies demonstrate any sort of geographical isolation.  He wrote:

“In a well-watered region of low relief, like Florida, no barriers to the migration of these snails exist, so that the geographic limits of such races are only vaguely defined. The shell characters are so variable that with single shells or small series the identity may often be in doubt.”

In the image below, clipped from Pilsbry’s Plate 7, the top row of shells (5a – 5f) were all borne by a Helisoma duryi population sampled from “near Lake Apopka,” the second row (6a – 6f) all from a population inhabiting Lake Eustis (Lake Co.), and the third row (7a – 7e) all from the Head of the Miami River.  This entire set of 17 shells he identified as varying subspecies of Helisoma duryi.  There is no difference between shells 5e, 5f, 6e, 6f, and any of the shells I collected from Lake Tarpon.

So again, I ask.  If not the shell morphology, what exactly is the difference between Helisoma duryi – particularly the subspecies that Pilsbry began calling H. duryi seminole in 1934 – and the earlier-described H. scalare?  The distinction that Henry Pilsbry drew in 1934 turned out to be entirely anatomical.  The duryi/scalare situation is very closely analogous to the duryi/trivolvis situation we reviewed at great length back on [9Feb21], involving many of the same anatomical features, and (indeed) the same illustrations of them.  So to refresh everybody’s memory, again:

It was upon Henry Pilsbry’s head that rested the crown of American Malacology, pretty much his entire career, from 1887 to 1957.  Frank Collins Baker, more experienced as a field biologist and more gifted as a scientist, studied under Pilsbry in 1889, and labored in his shadow thereafter, predeceasing his mentor by 15 years.  And to understand what I’m getting ready to tell you about scalare and duryi, you need to understand the relationship between Pilsbry and Baker.  A bit of familiarity with the reproductive plumbing of pulmonate gastropods will also be helpful, but not necessary.

From Pilsbry [2] Plate 7.

When not in use, pulmonate gastropods invert their penis – turn it outside in – to make a bag with the business end inside.  Figure (A) in the montage below shows the structure that Pilsbry (1934) simply called the Helisoma scalare “penis, unopened.”  It’s an (upside down) sack, with an opening in the bottom through which the penis everts for copulation.  The figure I’ve marked (B) shows a Helisoma scalare penis sack opened, Pilsbry’s “V” standing for “verge,” which is a polite name for the business end of the penis during copulation.  That organ Pilsbry has marked “pg” is the penial gland, which presumably supplies some sort of lubrication during copulation, or stimulation, heaven knows.

So, to distinguish the two nominal species of the subgenus Seminolina, scalare and duryi, Pilsbry focused exclusively upon differences he perceived in the penial gland.  In his description of his new scalariform subspecies H. duryi seminole, he wrote:

“I dissected specimens collected many years ago in Polk Co., Florida, by S. Hart Wright, and similar in shape to fig. 6d of Plate 7. The bodies are brittle, and only the penis was examined (figure C), cylindric, with the upper sac divided off inside by a thin rather high ridge. The stout conic verge projects into the lower sac. The penial gland is oblong with the smooth lateral borders folded in the alcoholic specimens, as in figure (C). This structure is quite unlike that found in H. scalare (B).”

And to reinforce the distinction, here is what Pilsbry said in his redescription of H. scalare:

“In the specimens of H. duryi seminole opened, the penial gland was found to differ [from H. scalare] in important details. It [the duryi penial gland] has a broad oblong face directed toward the cavity, with the lateral borders infolded in alcoholic specimens, as in figure (C). The division between upper and lower sacs of the penis is a single rather high thin ridge. The stouter shape of the verge in H. d. seminole may be due to greater contraction, as the specimens had evidently been killed in strong alcohol.”

Now moving forward ten years.  In addition to the three Pilsbry figures I have reproduced below F. C. Baker’s (1945) figure of the same organ – less artistic but more scientific (D).  Baker did not execute separate drawings for scalare and duryi.  This single figure was offered to represent the entire subgenus Seminolina, including scalare and duryi of all subspecies.

Penial complexes from Pilsbry [2] and Baker [3]

Baker dissected 35 individuals from the “Lake Butler” (now L. Tarpon) population of H. scalare, and populations of H. duryi from seven different sites, representing three subspecies.  Regarding the Lake Tarpon population, Baker was quick to pay homage to the Elderly Emperor:

“The genitalia of Helisoma scalare examined agree perfectly with the figures published by Pilsbry 1934.”

Turning to his H. duryi samples, Baker figured on his Plate 33 the “penial complexes” (Pilsbry’s “penis unopened”) from 12 different H. duryi individuals dissected from four populations of three different subspecies, all pushed, pulled, shrunk and extended into a myriad of diverse, blobby profiles.  And hidden among his observations was this single-line bombshell, directly contradicting the only distinction that Pilsbry had ever drawn between scalare and duryi:

“The penial gland in the duryi complex is of about the same shape as that organ in scalare.”

Poor Frank Collins Baker!  I can still feel the anguish seeping from page 132 of his planorbid monograph, here 80 years later.  The character of the penial gland that Pilsbry called “lateral borders infolded” is trivial at best, entirely artifactual if it ever existed.  Baker couldn’t confirm it in a dozen H. duryi sampled from four populations.  But neither could he risk offending his Emperor.  So, all he could do was to dissemble, which he did, five sentences later:

“The figures of the duryi complex agree with those by Pilsbry (1934).  As Pilsbry remarks on page 36, the anatomical differences are sufficient to separate scalare from duryi and its races.”

The bottom line for us today is, however, that there is no evidence of any morphological distinction whatsoever, shell or anatomical, heritable or otherwise, let alone any evidence of reproductive isolation, between the diverse planorbid populations found throughout Florida and around the world conventionally identified as Helisoma (Planorbella) duryi, and the earlier described planorbid populations of deeper, cooler and cleaner Floridian waters identified as Helisoma (Planorbella) scalareWetherby’s (1879) nomen duryi is a junior synonym of Jay’s (1839) scalaris or scalare [7].

But let’s save duryi at the subspecific level to describe populations of H. scalare bearing planispiral shells, shall we?  I hasten to remind everybody, once again, that the FWGNA has adopted the definition of the word subspecies in currency since the birth of the modern synthesis: “populations of the same species in different geographic locations with one or more distinguishing traits.”  No additively heritable basis for the shell morphological distinction between the typical scalariform morphology and the planispiral duryi morphology is necessary, or implied [8].

And I also hasten to remind my readership that the “different geographic locations” may differ at very small scales in freshwater gastropods.  See my essay of [18Feb05] for an example here in the Charleston area where populations of the duryi subspecies and the typical subspecies are separated by only a few meters.

As we have seen, the most obvious correlation seems to be with the habitat: scalariform populations inhabiting submerged macrophytes and benthic substrates in large, permanent clearwater lakes and springs absent contact with the surface, planispiral populations inhabiting emergent or floating macrophytes on the margins of ponds, ditches and riverine backwaters.

There is also a correlation with predator pressure: the scalariform populations of clearwater lakes suffering more fish predation, the planispiral populations more beset by invertebrate predators like crayfish and leeches.  And trematode parasites, apparently.  For completeness, here’s an interesting observation from Baker, page 134:

“The Helisoma duryi complex includes several races more or less heavily infested with parasitic worms.  These include normale, intercalare, eudiscus, and duryi.  Many specimens were so badly infested that most of the organs, especially the genitalia, were completely obliterated.  Helisoma scalare was the least affected.”

In conclusion.  Nothing I have written in this essay is intended as a criticism of Henry Pilsbry or (heaven forbid!) Frank Collins Baker, both of whose works stand today at the pinnacle of classical American malacology [9].  Pilsbry was The Emperor, and if in his judgement some wrinkle or fold in some gland or tube confirmed the specific status of some gastropod population somewhere, in late pre-modern systematic biology, that settled it.  Baker was a courtier, following in retinue behind.

I’d like to imagine myself in the story as a small boy watching the grand parade, naively observing that even if the margins of some particular gland in some particular snail really were folded in the particular fashion The Emperor decreed, naturally and not the result of some sort of artifact, it just wouldn’t matter anyway.

But alas, The Emperor, his Retinue and his Grand Parade have long, long passed, many years ago.  And I’m just sweeping up behind.


[1] Here’s a complete list of all essays previously posted on this blog relevant to the argument I am advancing this month:

  • Gigantic pulmonates [29Nov04]
  • Shell morphology, current, and substrate [18Feb05]
  • Juvenile Helisoma [9Sept20]
  • The Flat-topped Helisoma of The Everglades [5Oct20]
  • Foolish things with Helisoma duryi [9Nov20]
  • The Emperor Speaks [3Dec20]
  • Collected in turn one [5Jan21]
  • Dr. Henry A. Pilsbry was a jackass [26Jan21]
  • The Emperor, the Non-child, and the Not-short Duct [9Feb21]
  • In the Footsteps of the Comte de Castelnau [6Dec22]
  • The Helisoma from the Black Lagoon! [5Jan23]

[2] 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.

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

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

[5] This is quite possibly the most famous figure Pilsbry ever published.  It depicts the only overtly evolutionary thought that ever flickered through The Elderly Emperor’s mind, as far as I know.  It was reproduced on page 280 in Burch [6], and I dredged it up again for my Helisoma essay of [18Feb05].

[6] 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).

[7] Pilsbry re-spelled the feminine scalaris to the neuter scalare to agree in gender with the neuter noun-construct Helisoma.  His Imperial Majesty did not stoop to explain that fine point of Latin grammar himself, however.  My good buddy Harry Lee was much more helpful.

[8] For a complete discussion of the subspecies concept as adopted by the FWGNA project, see:

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

[9] Neither Pilsbry nor Baker was touched by the modern synthesis, although I’d like to think that Baker would have been receptive, had he survived beyond 1942.  This makes the 1934 work of Calvin Goodrich [10] all the more impressive, if you think about it, am I right?

[10] For an appreciation of Calvin Goodrich, see his brief bio, then review his 1934 masterwork:

  • The Legacy of Calvin Goodrich [23Jan07]
  • CPP Diary: The spurious Lithasia of Caney Fork [4Sept19]
  • Intrapopulation gene flow: Lithasia geniculata in the Duck River [7Dec21]

Thursday, January 5, 2023

The Helisoma from the Black Lagoon!

Last month [1] we toured all around Tallahassee and its immediate environs with the Comte de Castelnau, trying to figure out where The Count might have found a planorbid shell he gifted to John Clarkson Jay in 1838.  Jay described that peculiar flat-topped shell as Paludina scalaris, making wherever His Excellency might have picked it up the type locality of a species widespread and common throughout peninsular Florida.  And related in some very close way to Helisoma duryi (Wetherby 1879), which has been spread throughout the world.

Well, as the sun set on our first day of exploration, we had indeed found a couple Helisoma populations, both of which (alas!) bore disappointingly planispiral shells of dirt-common duryi morphology.  To find a population bearing the flat-topped “scalariform” morphology, we had resolved to venture further afield.


South and east of Tallahassee extend vast, marshy hinterlands drained by the St Marks River, with its primary tributary the Wakulla.  Although the formal classification of “Everglades” has today been reserved for regions further south down the Florida peninsula, much of the St Marks / Wakulla system might well have been colloquially referred to as everglades by its nineteenth-century denizens [2].  The hydraulics of the region are most unusual.  Picking up our story once again, in the words of Count Castelnau [3]:

"This river [the St. Marks] rises in Georgia, crosses Lake Mikasouky, sinks underground and soon comes forth as a pond at Brookhaven."

That area where the St. Marks “sinks underground” is today preserved in Natural Bridge State Park, about 13 miles SE of Tallahassee (G, map below).  In March of 1865, less than thirty years after The Count’s visit, a joint expeditionary force under the command of Maj. Gen. John Newton landed at the St. Marks Lighthouse 10 miles downstream and marched north intent on capturing the state capitol.  Newton was repulsed at Natural Bridge by a combined force of Florida cavalry, artillery, and militia, including cadets from the institution of higher learning that would become Florida State University.  Tallahassee was the only Confederate capitol east of the Mississippi River that did not fall to Yankees during the war.

I found The St Marks River forbiddingly black and deep as it enters Natural Bridge State Park, with very little freshwater gastropod habitat in evidence.  But in the nearby Natural Bridge Spring I recorded eight species, including more Helisoma bearing disappointingly-planispiral shells of the duryi type [4].

Continuing downstream on the St Marks River, the Count apparently visited the town of Magnolia, founded by four brothers from the state of Maine as a cotton trading port.   The town is classified as “extinct” by the state of Florida today, but even by 1837, it was apparently struggling:

"Magnolia is a little village, if this name may be given to two or three houses, situated seventeen miles from the Gulf of Mexico on the St. Marks River; it was built in 1827. It is almost abandoned today because of fear of the Seminole Indians who several times have committed massacres in the vicinity. The soil is fertile and the banks of the river are charming."

The historical footprint of Magnolia is approximately 1 mile north of the present-day town of Newport, where US98 crosses the St. Marks River (H).  I couldn’t find any public access to the river in Newport, but no decent freshwater gastropod habitat was visible from the bridge in any case, so screw it.


But now for the highlight of our visits to Florida, both of the Count’s in 1837 and my own in early 2021.  About 13 miles due south of Tallahassee is the aquatic wonderland of Wakulla Springs, “the largest and deepest natural spring in the world [5].”  Castelnau made his approach via water, rowing upstream from the town of St. Marks “by great effort, through snags.”

"Our little expedition left St. Marks at sunrise, and having gone around the point where the old fort is, entered Wakulla River; it is at first very wide and on its marshy shores there are a few scattered pines…  We had to struggle against a current of about a league per hour; the shores are very marshy and flooded, the river bed is covered with high grass which blocks the passage; in some places very big bushy canes also increase the difficulty of travel by water. We soon arrived among vast cypress groves whose trees are grouped in the form of islands; everywhere fallen tree trunks blocked our way."

I launched my kayak into the Wakulla River at the Shadeville Road bridge (I) and spent a lovely couple hours sampling the clear, cool, rich waters about three miles downstream from the spring.  I was especially charmed by the big Nerita reclivata grazing across the surfaces of the emergent Sagittaria grass beds, the first freshwater nerites I had ever seen in the wild [click to download an action shot.]

The freshwater gastropod fauna was otherwise disappointing, however; a gigantic population of grotesque Melanoides tuberculata outnumbering the native Pleurocera floridensis about a zillion-to-one.  I found no living hydrobioids, indeed counting myself lucky to net up a singleton Notogillia shell.  As for Helisoma, I was able to find exactly N = 2 in two hours of effort, both bearing entirely unremarkable shells of planispiral morphology.


And any thoughts I might have entertained about kayaking upstream to the springhead were dashed by a curtain of fencing hung across the entire width of the river above the bridge, festooned with signage most uncordial.  I loaded my kayak back into the truck and completed my journey to Wakulla Springs in routine, 21st century fashion. 

"The spring is oval in form and three hundred feet wide. By taking soundings we found that it was 76 feet deep. We were told however that in some places it was 100 feet deep; its water is wonderfully pure, and one can distinguish the smallest objects that are on the bottom;  Huge flocks of birds came to give life to the scene, we noticed especially among them beautiful herons of a dazzling white, pelicans with huge beaks provided with a big pocket below them, numerous long legged water fowl, the pretty Carolina parrakeet, etc., etc."

The Count did not mention any human residents of the area at his visit in 1837, but by 1875 enterprising locals were hosting guests and offering glass bottom boat tours of the spring.  Large scale commercial development was delayed until the 1920s but kicked into high gear in 1934, when financier Edward Ball purchased all the acreage around the spring and built a world-class resort hotel.

Wakulla Springs hosted US Army training maneuvers during World War II, including the detonation of underwater explosives [6].  In the postwar heyday that followed, the springs served as the filming location for at least one or two Tarzan movies, plus the 1954 cult classic, “Creature From The Black Lagoon.”  The property was acquired by the Florida State Park system in 1986, who have continued to run the hotel, beach, and boat tours very much in business.

Paying my $4 admission price as I passed through the contact station, the ranger glanced to the back of my pickup, noticed my kayak, and inquired, suspiciously, “You’re not planning to launch that in here, are you?”  “Gracious no!” I replied, “Such thoughts could not be further from my mind.”  “Good,” he cautioned, “The springs are a protected natural area.”  Protected from biologists in kayaks, apparently, but not from glass bottom motorboats or amphibious combat vehicles?


I had planned a rather unconventional itinerary for my visit, stopping first near the park entrance at the Sally Ward Spring Run (J). It materializes that there is a small, unfamous, and relatively ordinary spring in the cypress swamp upstream from the main tourist attraction, feeding into the spectacular head of the Wakulla River, within which the gill-faced Creatures lurk and upon which the glass-bottomed boats motor.

I found the malacofauna of the spring run similar to that I had just sampled in the main Wakulla River three miles downstream, although healthier [7].  And once again, dwelling on the muddy margins of the stream I found a sparse Helisoma population bearing shells of quite unremarkable, planispiral morphology, no different from the Helisoma I had seen at the Shadeville Rd bridge (I), or at the Natural Bridge Spring earlier in the morning (G), or indeed, on my explorations around Tallahassee the previous day.

Sally Ward Spring
Preliminary scouting work complete, I parked my truck at the back of the main parking lot for the tourist attraction and shucked off my hip waders so as not to attract attention, selecting instead a pair of well-worn Converse that I didn’t mind getting wet. I left my dipnet in the truck for the same reason, fearful that any overt show of scientific activity might be interpreted as threatening to the “protected natural area.”  Then putting my hands in my pockets, I strolled casually toward the waterfront (K).

The swimming beach was quiet on the brisk February morning of my visit and the tour boats not running.  But my attention was called to a hive of activity around the diving platform shown at the far left in the photo above.  Joining the throng on the top deck I was able to spy several manatees floating motionless in the crystalline waters below.


Oddly enough, however, I found myself more enchanted by the rooted-submerged macrophytic flora of the spring bottom than by the charismatic megafauna floating over it.  The waving jungles of Sagittaria and Vallisneria interspersed with white sand bottom were simply magical.  Pretty little fish and minnows nibbling about everywhere.  A coot paddled under my gaze, oblivious.  Where the hell are the snails, I thought to myself.


Where the hell, indeed?  I waded the entire shoreline accessible from the developed side, including weedy margins and all around the docks, to a depth of a foot or so, and did not find so much as a crap Physa.  Not a limpet on a leaf.  I can’t remember the last time I was skunked so thoroughly for so much effort.


Ah, but.  Around the shorelines of the Wakulla Spring pool one could hardly fail to note extensive deposits of relict shells.  And common among those relicts were Helisoma shells of the exact flat-top morphology demonstrated by the specimen presented to John Clarkson Jay by Comte de Castelnau in 1837.  I feel certain that Wakulla Springs is the type locality of Paludina scalaris Jay 1839.  For this conclusion I offer four lines of support:

Beach at Wakulla Springs

First, it seems quite possible that a living population of Helisoma scalare may inhabit Wakulla Springs today, and I simply missed it.  My readership will remember that the population of flat-topped Helisoma I sampled at the Forty-mile Bend were cowering in aquatic vegetation submerged several feet below the water surface [5Oct20].  I was only able to collect them by net, from a kayak.  Absent either of these tools in February of 2021, and stuck on the highly-disturbed south shore of the spring, I was simply unable to sample the habitat adequately.


Second.  Even if no flat-topped Helisoma population inhabits Wakulla Spring today, it is certainly possible that a living population existed in 1837 [8].  Those relict shells I collected perhaps a foot above the waterline of the spring pool in early 2021 were not necessarily old.  In addition to the Helisoma, the figure above depicts one Pleurocera floridensis shell and two shells of Melanoides tuberculata, an exotic not recorded from anywhere in Florida until 1966 [10].  Might my chalky-white Helisoma scalare shell date but only to circa 1966, as well?


Third, even if no living population of Helisoma inhabited Wakulla Springs in 1837, the type shell presented by the Comte de Castelnau to John Clarkson Jay in 1839 was not live collected, either.  Indeed, it would seem more in keeping with the sensitivity of French nobility to pick up a clean white shell from the beach than yank some greenish-brown booger from the weeds, am I right?  That's Jay's AMNH type specimen refigured under the Creature mask way up at top of the present essay, to refresh your memory.

And finally.  I have been unable to find any scalariform Helisoma anywhere else The Count might have visited in 1837.  Of the ten other Castelnau sites I re-visited in 2021, six yielded no Helisoma at all, and four yielded Helisoma bearing unremarkable planispiral morphology.


All of which brings us back, one more time, to the question I’ve been nibbling around the edges of for nine essays now, and still not properly bit.  What is the relationship between Helisoma scalare and all those populations of large planorbids bearing unremarkable planispiral shells, traditionally identified as Helisoma duryi?  Next time we’ll answer that question.  I promise.


[1] If you’re just joining us.  This is the ninth essay in a long-running series that had its roots in 2005, picked up steam in 2020-21, and just resumed last month.  I won’t suggest that you go back and read the entire series unless you’re seriously interested in the science.  But the present essay won’t make much sense unless you’ve read my 6Dec22 post, at the minimum:

  • Shell morphology, current, and substrate [18Feb05]
  • Juvenile Helisoma [9Sept20]
  • The Flat-topped Helisoma of The Everglades [5Oct20]
  • Foolish things with Helisoma duryi [9Nov20]
  • The Emperor Speaks [3Dec20]
  • Collected in turn one [5Jan21]
  • Dr. Henry A. Pilsbry was a jackass [26Jan21]
  • In the Footsteps of the Comte de Castelnau [6Dec22]

[2] It will be remembered from last month’s essay [6Dec22] that Jay gave the type locality of Paludina scalaris as “The Everglades of Florida.”  And it will also be remembered from [5Oct20] that regions around Tallahassee do not qualify as “Everglades” today.


[3] This month’s Castelnau quotes are extracted from:

  • Castelnau, F., A.R. Seymour and M.F. Boyd (1948) Essay on Middle Florida, 1837 – 1838.  The Florida Historical Quarterly 26(3): 199 – 255.

[4] The freshwater gastropod fauna of Natural Bridge Spring: Viviparus goodrichi, Pleurocera floridensis, Spilochlamys conica (topotypic!), Amnicola limosa, Physa carolinae, Laevapex fuscus, Ferrissia fragilis, and the planispiral Helisoma.


[5] Here I’m quoting wakullasprings.org.  They did not share any data on the millions of other springs they must have measured worldwide to arrive at their conclusion.


[6] US Army training video, from the State Library and Archives of Florida:

Wakulla Springs Military Training and Underwater Explosions

[7] The Sally Ward Spring Run malacofauna is dominated by large populations of Pleurocera floridensis and Spilochlamys conica, with Melanoides nowhere in evidence.  Both Ferrissia rivularis and Laevapex cling to the macrophytes blades, with planispiral Helisoma and Physa carolinae populations grazing sparsely at the stream edges.  Scrappy evidence of Viviparus & Campeloma.


[8] My search of the worldwide idigbio database [9] for Planorbidae + Wakulla returned a single record in the University of Florida Museum that might be of interest: UF4855, collected from Wakulla Springs by J. Richardson in 1938.  That lot is identified as “Planorbella duryi.”  Is the shell morphology of UF4855 scalariform or vanilla planispiral?  I do not know.


[9] For more about the IdigBio internet resource, see:

  • 20 Years of Progress in the Museums [22May19]

[10] Clench, W.J. (1969) Melanoides tuberculata (Muller) in Florida.  Nautilus 83: 72.