Dr. Rob Dillon, Coordinator

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 state 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 (H), 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.

Tuesday, December 6, 2022

In the Footsteps of the Comte de Castelnau

Way back in September of 2020 I concluded a mundane essay about juvenile shell morphology with the following deceptively difficult question: “What, exactly, are Helisoma scalare and Helisoma duryi?

Over the four months and five essays that followed [1], we were able to establish that both taxa are big Floridian planorbids, sometimes assigned to the genus “Planorbella” for no reason whatsoever [9Sept20], set aside in a subgenus Seminolina by Henry Pilsbry [2] in 1934 [3Dec20].  The difference between the two nominal species lies in the shell coiling, Helisoma scalare being distinguished by a peculiar flat-topped “scalariform” morphology.  Helisoma duryi, on the other hand, usually bears shells of the typical planispiral type, so typical, in fact, that they are often very difficult to distinguish from those borne by dirt-common Helisoma trivolvis populations widespread across the rest of North America [5Jan21].

Ultimately, however, I only answered half of the question I posed in September of 2020.  Across the six total essays I posted on the subject, I spent 50% of my time obsessing about Helisoma duryi, focusing especially on their protean variability in shell morphology, “short, fat, tall, skinny, and all over the place” [5Jan21].  Then I spent 30% of my time obsessing about Helisoma trivolvis and 20% of my time obsessing about Henry Pilsbry [26Jan21], never really touching on Helisoma scalare at all.  So, this month let’s back up and get a fresh start at the scalare half of the question, shall we?

P. scalaris, holotype [4]
John Clarkson Jay (1808 – 1891) was the grandson of Founding Father John Jay, the first chief justice of the United States and co-author of The Federalist Papers.  I gather that by the 19th century the Jay family had acquired substantial means.  John Clarkson was trained as a physician, but apparently had enough liquid capital and leisure time to amass what was reputedly “the most complete and valuable collection of shells in the United States.”  He published catalogues of his shell collection in several editions 1835 – 1852, to which he appended “descriptions of new or rare species.”  And it was in John Clarkson Jay’s third edition of 1839 [3] that the world was first introduced to “Paludina scalaris, Nobis.  Habitat, Everglades of Florida.”  After a one-sentence description of the shell, Jay wrote, “It was presented to me by Count Castelneau.”

Jay’s holotype (AMNH 56111) is still held by the American Museum of Natural History today [4], looking just as dramatically flat-topped as Jay figured it in 1839.  Jay’s nomen “scalaris” or scalare [5] is the sixth oldest nomen applied to any of the large [6] North American planorbids, after trivolvis, glabratus [7], campanulata, corpulentum and anceps.

But if there is one lesson I have learned over my many months, indeed years, of struggling with the taxonomy of Florida freshwater gastropods, it is that “The Everglades” is a big place.  In our essay of [5Oct20] we learned that the Everglades Ecoregion, as formally defined by the Feds, extends over all or part of 18 South Florida counties, some 7,800 square miles.  And in our essay of [3Dec20] we learned that when Charles Dury told Albert Wetherby that he collected a sample of planorbids in “The Everglades of Florida” in 1879, he meant in Volusia County, a couple hundred miles north of anyplace that the Feds would call Everglades today.  What was “The Everglades” to a French Count in 1839?

Fortunately, Henry Pilsbry left us a very helpful clue in 1934, just as he did with Wetherby’s duryi.  Quoting the Elderly Emperor verbatim [2]:

“Jay's locality was ‘Everglades of Florida, presented to me by Count Castelneau;’ that is, le Comte Franqois (or Francis) de Castelnau, who travelled in the southeastern states in the thirties and early forties. He published several papers in Bull. de la Soc. de Giographie, 1839-1842, in the last (vol. 18, p. 252) alluding to his work on Florida, which I have been unable to find in Philadelphia libraries. Probably the type locality can be recovered by looking up Castelnau's itinerary in this book.”

So here in the 21st century, Count Castelnau’s papers [8] are much easier to get hold of than they were in 1934.  And even better, in 1948 a University of Florida historian named Arthur R. Seymour translated Castelnau’s work into English and republished them in The Florida Historical Quarterly [9].  And it materializes that when Castelnau said “The Everglades,” he meant the Florida panhandle, somewhere around Tallahassee.

Castlenau left Charleston, my hometown, in mid-November 1837, travelling first by rail to Augusta, then on “a very narrow and detestable road” through the heart of Georgia.  His most interesting adventure southbound took place in the “ramshackle” [10] village of Bainbridge, where “about one hundred Chattahoutchi Indians, who are allies of the whites, arrived bringing with them about sixty hostile Creeks or Muscogis.”  The Count was invited to join the Chattahoutchis for “an entire night of dancing, drinking and shouting.”

The Count arrived in Tallahassee after two weeks on the trail, exploring about the vicinity until mid-March of 1838, leaving us vivid accounts (and not a few interesting illustrations) of the small town and its environs, before returning to Charleston by way of steamer up the Apalachicola/ Chattahoochee River.  But alas, at no time in any of his writings did he address the most important subject, the snails he encountered along the way.

And so it came to pass that in February of 2021 I pointed my trusty [11] Mazda pickup south on I-95, Arthur Seymour’s translation of Castelnau’s travelogue on the passenger seat, outward bound on yet another planorbid-themed adventure.  My plan was to visit every body of water mentioned by The Count in his Florida explorations, or at least representatives thereof, searching for a topotypic population of Helisoma scalare (Jay 1839).  In the account that follows, I have interleaved quotes from Castelnau’s travels with notes from my own fieldbook.

We passed over the Oclockone [Ochlockonee] River and the Little River whose banks are delightful, then finding again pine woods we reached in the evening Tallahassee, the end of our [outbound] trip.

The Ochlockonee is what I would call (from my Carolina Lowcountry perspective) a typical blackwater river.  I launched my kayak at the boat ramp under the US90 bridge (A) and paddled upstream around the bend and could find very little habitat for freshwater gastropods of any sort – no submerged or floating vegetation, indeed almost no vegetation at the margins.

Numerous springs exist in the neighborhood and from one of them comes a pretty stream of water that after having wound around the eastern part of the city [Tallahassee] runs into the forest and forms a charming waterfall about sixteen feet high; it runs then into a ravine hollowed out of limestone and disappears underground quarter of a mile farther.

It is not uncommon in this part of the world for cities to have been founded around notable springs.  Huntsville and Tuscumbia, Alabama, come to mind in this regard.  In both of those cases, city fathers have set aside parkland in the heart of the modern city and added all manner of improvements to the springs, sometimes (in some cases, maybe) preserving some ghost of the native macrobenthos in the process.  Alas, the greatest disappointment of my fieldtrip came early, as I arrived at Tallahassee’s midtown “Cascades Park” (B).

Cascades Park

The montage above shows the modern park, with Castelnau’s original 1837 figure in the upper right corner.  Notice the landscaping beds around the modern spring run, specifically designed to discourage park visitors from approaching the water.  Little signs have been placed at the front of those beds, warning us (and our pets) not to enter the “stormwater.”  And alas, that is indeed a stormwater sewer at red arrow in photo below, the water emanating from which bears a dark, suspiciously-olive color.  I spent about 10 – 15 minutes poking around the water in desultory manner, picking up Physa, and moved on.

To the east of this town extend the lands offered by the government of the United States to General Lafayette in which is a pretty lake that bears his name. No words can convey the beauty of these sheets of water which scattered in great numbers in the midst of virgin forests in Middle Florida; they are filled with fish of many sorts and their surface is everywhere enlivened by clouds of aquatic birds, above which flies constantly the bald eagle. Among the denizens of these lakes we must mention the soft shelled turtles, as well as the alligators that are abundant there; these last reach ordinarily length of twelve feet, and although little to be feared, by their repulsive aspect they inspire terror in persons not accustomed to seeing them.

The Federal Government did indeed grant the Marquis de Lafayette a 36-square-mile tract east of Tallahassee in 1824, in gratitude for his military service to our young republic.  Lafayette never visited, however, and the entire grant had been sold off piecemeal by 1855.  The Lake Lafayette to which Castelnau referred was divided into three sections with dikes, its central section dredged for recreational use, and given the odd name “Piney Z” Lake, in honor of a nearby plantation.

Lower Lake Lafayette

I visited both the central Piney Z Lake (C) and Lower Lake Lafayette (D) at the town of Chaires.  The former was warm and trashy, and hosted but Physa and Pomacea maculata.  I had great hope for the latter, however, which I found to be a Lake in Name Only (“LINO”), choked with aquatic vegetation of all sorts.  Indeed, I enjoyed one of my prettiest paddles in recent memory, spoiled only by the thunderstorm evident on the horizon of the photo above.  And the malacofauna, which comprised nothing but Physa and Pomacea, again.

Lake Jackson is situated a league and a half [north] from Tallahassee. According to the Indians, its water gushed forth suddenly from under the ground, covering a vast cultivated plain. It is certain that trees are still to be seen there, and that when the water is low Indian trails may be noticed.

The hydraulics of Lake Jackson are indeed strange.  The water level appeared at least ten feet below bank full on the morning I visited at site (E), boat ramps high and dry.  I asked a local angler if this little patch of Florida might be suffering a drought, even as rainstorms daily drenched the remainder of the Sunshine State, coast to coast.  He replied in the negative, explaining that the Lake has a small “closed basin,” and had gone entirely dry on several occasions in his lifetime.  I thought (to myself) that a closed basin would lead one to expect high water in times as diluvian as those we were currently experiencing.

Lake Munson
In light of this intelligence, I suppose my readership will not be surprised to learn that the malacofauna of Lake Jackson depauperate.  In addition to the trash Pomacea I did find exactly N = 1 juvenile Helisoma.  Which I hoped, upon my departure, that I would not be forced to return and augment.

A great number of lakes or ponds are scattered to the south of Tallahassee. All these lakes are surrounded by dense woods, which are scattered some fine cotton and sugar plantations. Most of them seem to be sinking leaving on their shores a great deal of fertile land. are often almost entirely covered with rushes and plants. In their water are found great numbers water serpents (mocassins), soft-shelled turtles, gators, among which swim large flocks of aquatic their shores are crowded with bands of deer and many white headed eagles soar over them or the oaks and the immense magnolias that are shores.

Lake Munson is a good representative of a “lake scattered to the south of Tallahassee.”  I paddled around the west edge to no effect.  But at the outlet dam (F), I was pleased to discover a healthy population of Helisoma.  I was simultaneously disappointed, however, by the typical, planispiral shells they bore upon their backs.  None, alas, demonstrated the “scalariform” shell morphology that made John Clarkson Jay’s Paludina scalaris so distinctive.

As the sun set on a long, wet day touring the diverse rivers, springs, lakes and ponds of Tallahassee and vicinity, I admit to experiencing a bit of frustration.  True, I had found a couple scrappy populations of Helisoma.  But none bore shells even remotely matching Jay’s 1839 type specimen in the collection of the American Museum way up in New York City.  Were my hopes to be blighted?  Stay tuned!

Lake Munson at the outlet


[1] Here is my complete series on Helisoma duryi and the flat-topped Helisoma of Florida to date:

  • 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]

[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] Jay, J.C. (1839)  A catalogue of the shells, arranged according to the Lamarckian system; together with descriptions of rare species, contained in the collection of John C. Jay, M.D.  Third Edition.  Wiley & Putnam, New York.

[4] I thank Ms. Lily Berniker of the AMNH for her prompt and courteous attention to my request for this photograph.

[5] Pilsbry [2] re-spelled Jay's (feminine) scalaris to the neuter scalare to agree with the gender of the neuter noun construct Helisoma.  I thank my good buddy Harry Lee for this insight.

[6] Pilsbry divided all the North American Planorbidae into two subsections, the large ones and the not-large ones [5].  John Clarkson Jay’s scalaris is the sixth oldest name for a large one.  There are also five older names for not-large North American planorbids, which do not concern us here, but for the record: parvus, deflectus, crista, armigera, and exacuous.

[7] Thomas Say gave the type locality for his (1818) Planorbis glabratus as “Charleston, South Carolina.”  Pilsbry questioned that locality, but I believe it.  We'll come back to this subject in a couple months.

[8] Here are the originals:

  • Castelnau, F. (1839) Note sur la Source de la Rivière de Wakulla dans la Floride. Bulletin de la Société de Géographie 11 (2): 242 – 247.
  • Castelnau, F. (1842) Vues et Souvenirs de l’Amérique du Nord. Paris.
  • Castelnau, F. (1842) Note de deux Itinéraries de Charleston à Tallahassée.  Bulletin de la Société de Géographie 18 (2): 241 – 259.
  • Castelnau, F. (1843) Essai sur la Floride du Milieu.  Nouvelles Annales des Voyages et des Sciences Géographiques 110, 4: 129 – 208.

[9] And here are the translations:

  • Castelnau, F., A.R. Seymour and M.F. Boyd (1948) Essay on Middle Florida, 1837 – 1838.  The Florida Historical Quarterly 26(3): 199 – 255.
  • Seymour, A.R. and F. Castelnau (1948) Comte de Castelnau in Middle Florida, 1837 – 1838.  Notes concerning two itineraries from Charleston to Tallahassee.  The Florida Historical Quarterly 26(4): 300 -324.

[10] “Here I was able to form an idea of the character of the people of this region, by noticing the ramshackle condition of the ordinary houses, all the windows of which were broken and the doors broken down.  I asked the cause of it and I learned that a few days before all of the inhabitants having got drunk and committed this havoc.”

[11] Five of those letters, anyway.

Thursday, November 3, 2022

The SNHTHICACBW Marstonia 6: pachyta

Last time we reviewed the minor hydrobioid taxon Marstonia from its origin as a subgenus in 1926 through its 1977 promotion by Fred Thompson, its 1994 death at the hands of Bob Hershler, and its 2002 resurrection by the dynamic duo of Thompson and Hershler working together.  And we focused on a subset of Marstonia that Thompson called, “small narrow hydrobiids that have in common a carinate body whorl,” abbreviated “SNHTHICACBW.”  This subset includes M. letsoni from way up north, which we reviewed in [19Jan16] and [5Feb16], and which in retrospect, might have been numbered 1 and 2 in this series.  And the subset also includes M. ozarkensis, which we reviewed in [10Feb20] and [16Mar20], which in retrospect might have been numbered SNHTHICACBW installments 3 and 4.

Then after laying all that groundwork, which took almost 700 words, which is approaching my target length for an entire essay, I blathered on another 1,400 words about the original member of the SNHTHICACBW group, Marstonia scalariformis.  We focused especially on the ACBW part of the formula, “a carinate body whorl,” dwelling at length on the variability that carination can demonstrate.  And at the eagerly anticipated end of last month’s essay, we concluded that the ranges of these little hydrobiids can be vast.  The range of M. scalariformis seems to extend from Illinois to Alabama.  And that they are obscure.  You will not find a population of SNHTHICACBW Marstonia unless you look sharp and employ special techniques.

So, when last we left our intrepid malacologist, he was standing knee-deep in the Flint River at Cherrytree, Alabama, washing stones into a sawed-off trash can (Site CT on the map way down below).  He was indeed finding Marstonia scalariformis.  But that was not all.

The four hydrobioids of the Flint River

There are four hydrobioids inhabiting the dark recesses of rocks and organic debris at Cherrytree, as figured above.  The Marstonia scalariformis we beat to death last month.  We’ll feature the lithoglyphid Somatogyrus populations in a pair of essays to be posted later this winter.  Maybe we’ll come back to Marstonia arga at some time further in the future [1].  What is that fourth hydrobiid?   What is Marstonia pachyta?

About three paragraphs into the first 700 words of blather I published last month I mentioned that when Thompson [2] initially elevated Marstonia to the genus level in 1977 he described five new species.  Among these was a snail “known to occur only in Limestone Creek and Piney Creek, Limestone County, Alabama” that “is readily identified by characteristics of both its verge (penis) and shell.”  That new species was a not-especially-small, not-particularly-narrow hydrobiid without a notably-carinate body whorl that he called Marstonia pachyta.

Thompson figured the M. pachyta penis as demonstrating a typical spatulate or bladelike form featuring three glandular areas, which I have labelled using Bob Hershler’s system as a pair of terminal glands (Tg) and a ventral gland (Vg) in the figure below.  (Thompson also figured another M. pachyta penis missing a second Tg. Bookmark that for later.)  Bob Hershler [3] came behind Thompson in 1994 and re-drew the essentially identical figure I have reproduced in the bottom half of the figure as well.

M. pachyta penis [4]
Regarding the shell morphology of his Marstonia pachyta, Thompson described the shape as “ovate conical,” and gave the adult length as ranging 3.3 – 4.0 mm.  The little sample figured below came from the type locality in Limestone Creek, east of Mooresville, AL (marked MV on the map way down below).

And regarding the range.  Although at the 1977 writing of his description Thompson was only aware of M. pachyta populations in Limestone and Piney Creeks, on 15Aug2000 he collected a sample from Bradford Creek at Martin Road [5] about 7 miles east (marked MR below), and on 16Aug2000 he collected a sample from Round Island Creek at Nuclear Plant Road [6], about 10 miles west (marked NP below).

From Bradford Creek it is just 18 miles further east to the Flint River, on the other side of Huntsville.  But here is yet another peculiar lapse in the long, strange career of Fred Thompson.  As far as I can tell, Thompson only spent one, single day collecting in the entire 500 square mile Flint River subdrainage, during which time he never recorded a single hydrobioid.  The freshwater gastropod collection of the FLMNH holds exactly N = 17 lots collected by Fred Thompson from anywhere in the Flint River or its tributaries, from seven sites he visited on Saturday, 27Sept69.  Among these lots are 16 of pleurocerids and 1 of Laevapex fuscus.  Zero hydrobiids of any species [8].

For comparison, Thompson collected 90 freshwater gastropod lots (48 hydrobiids) from Limestone Creek over his long career.  He then seems to have travelled 25 miles west to the Flint, crossed it barely wetting a boot toe, travelled another 10 miles further west, and collected 39 freshwater gastropod lots (8 hydrobiids) from the Paint Rock River.  Does it seem a bit irresponsible to make statements of the form “known to occur only in Limestone Creek and Piney Creek” when you haven’t even looked in the (biologically very similar) Flint River 25 miles away?  I don’t know.  I’ve probably done the same sort of thing myself.

Marstonia pachyta from Limestone Ck, AL

All of which brings us back, yet a third time, to yours truly standing knee-deep in the Flint River at Cherrytree, AL (site CT).  As my readership most certainly will have been able to divine by this point, what I was finding in the bottom of my sawed-off trash can was important.  Yes, a population of M. pachyta does inhabit the Flint River, matching the shell and penial morphology of the Limestone Creek type population in all respects.  And most of the shells are indeed “ovate-conical” as described by Thompson in 1977.  They are a bit smaller-bodied, however, and some of them are beginning to show a little bit of carination on the body whorl.  Yes, you heard me right.  They are beginning to look like SNHTHICACBW Marstonia.

Ten miles east of the Flint, the next south-draining tributary of the Tennessee River deep enough to wet your mule is the Paint Rock River.  It was from the Paint Rock 0.7 mi east of Cedar Point (CP) that Fred Thompson in 2005 described a new SNHTHICACBW species, Marstonia angulobasis [9].  Thompson distinguished his M. angulobasis by its shell of “minute size” (adulthood only 2.5 mm SL), bearing flattened whorls bordered at the periphery by a distinct angle or cord.  He characterized the penis as bearing “a terminal small apocrine gland.”  That’s what Hershler would have called a “terminal gland” and abbreviated “Tg.”

Tennessee drainages of North Alabama

So about seven paragraphs above, I asked you to “bookmark” the tidbit that Fred Thompson also “figured one M. pachyta penis missing a second Tg.”  The dorsal and ventral aspects of that pachyta penis (his Figs 13C and 13D) are reproduced in the top half of the figure below, compared to his figure of the penis of M. angulobasis below.  And let me ask you a rhetorical question.  If the M. pachyta penis can have 2Tg+1Vg, or 1Tg+1Vg, could it also have 1Tg+0Vg [10]?

Regarding the shell morphology of the Marstonia population inhabiting the Paint Rock River, see figures A and B below.  Thompson collected his type lot on a canoe trip, at a spot not readily accessible.  But he also listed “other specimens examined” from Butler Mill, about 2 miles downstream.  My observations at Butler Mill (BM) suggest a Marstonia population bearing shells quite variable in their “distinct angle or cord,” or carination, or keel, or whatever anybody would like to call it.  Some of them (like B below) show one, and some of them (like A below) do not.

In my September post [7Sept22] I went to great lengths to demonstrate that the distribution of glands on the Marstonia penis shows a great deal of intrapopulation variability.  And in last month’s post [4Oct22] I went to great lengths to demonstrate intrapopulation variation in the shell carination.  The weight of the evidence before us does not suggest that Thompson’s M. angulobasis is specifically distinct from his M. pachyta.

pachyta & angulobasis [11]

But let us save Thompson’s nomen “angulobasis” at the subspecific level, shall we?  Let us henceforth refer to populations of M. pachyta bearing carinate body whorls as “Marstonia pachyta angulobasis Thompson 2005."  And let us remember, as we do, that the FWGNA Project has adopted the definition of that term as it has been understood since the birth of the modern synthesis, “populations of the same species in different geographic locations, with one or more distinguishing traits,” which means exactly what it says, neither more nor less [12].

Now let me go back and pick up those other themes from last month’s post, that business about SNHTHICACBW Marstonia being widespread and obscure.  Although it will always be difficult for field biologists to find populations of such obscure little creatures looking for them, one might not be surprised to find them pop up in quantitative macrobenthic samples.

Over the last few years, I have been blessed to develop a professional relationship Ms. Debbie Arnwine, Ms. Patricia Alicea, and Ms. Carrie Perry of the Tennessee DWR in Nashville who, in the course of their routine duties, collect and sort huge numbers of quantitative macrobenthic samples collected from all over the Volunteer State.  These they hold for some years, but ultimately discard.

Sorting through hundreds of old samples released to us by the TNDEC-DWR, Bob Winters and I have discovered SNHTHICACBW hydrobiids identifiable as Marstonia pachyta angulobasis in three tributaries of the Cumberland River, perhaps 100 miles north of the North Alabama focus of the present essay: Smith Fork of the Caney System (C, below), the West Fork Stones River south of Nashville (D, below) and in Spring Creek of the Red River system almost to the Kentucky line (unfigured).  In fact, it seems possible to us that a single, enigmatic SNHTHICACBW Marstonia shell recovered by our colleague Ryan Evans from the bank of the Elkhorn Creek north of Frankfort, KY, might represent M. pachyta angulobasis, rather than M. letsoni as we have tentatively identified it [13].

A,B = Paint Rock River, C = Smith Fork, D = W.Fk. Stones River

So now has come the time to sum up, over all six of the essays I have contributed on the SNHTHICACBW Marstonia.  In 1977 Fred Thompson recognized a group he called, “small narrow hydrobiids that have in common a carinate body whorl,” comprising four specific nomina: scalariformis, letsoni, wabashensis, and ozarkensis.  Since that date wabashensis has been synonymized, while pachyta and angulobasis added.

Populations identified by two of those specific nomina, scalariformis and pachyta, demonstrate reproductive isolation where the co-occur in the Flint River at Cherrytree, Alabama.  Their shells are distinctive, those of the former bearing a strong carination extending higher than the body whorl, those of the latter occasionally bearing weak carination on the body whorl only.  Their penial morphology is also distinctive, that of scalariformis quite slender, that of pachyta bladelike.  These are two good biological species.

Evidence presented here suggests that angulobasis is a subspecies of pachyta.  The data on penial morphology we reviewed back in 2016 suggests that letsoni has affinities with scalariformis.  The evidence we reviewed in 2020 was too fragmentary to offer any hypothesis whatsoever on ozarkensis.

And finally.  All of these tiny little snails are widespread and obscure.  Their ranges can extend over many, many states.  They are not endemic to anywhere; they are epidemic everywhere across most of the eastern interior.  Populations come, and populations go.  You cannot find them.  Opening my thesaurus and dumping it wholesale onto the computer screen flickering before you, the SNHTHICACBW Marstonia are shadowy, secretive, enigmatic, mysterious, and obscure.


[1] Thompson [2] described Marstonia arga from Guntersville Reservoir in 1977, but it has since spread up the impounded Tennessee to the vicinity of Knoxville, and throughout the impounded Cumberland River as well.  It’s an evolutionary winner!  Seems unfair to ding the TVA for extincting some species without crediting them for carp, kudzu, and M. arga, doesn’t it?

[2] Thompson, F.G. (1977) The hydrobiid snail genus Marstonia.  Bulletin of the Florida State Museum 21(3):113-158.

[3] Hershler, R. (1994)  A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae).  Smithsonian Contributions to Zoology 554: 1 - 115.

[4] Above, Marstonia pachyta penis modified from Thompson [2] figure 13A and 13B.  Below, Marstonia pachyta penis from Hershler [3] figure 53a.  Dorsal on left, ventral on right. Tg = terminal glands, Vg = ventral gland, P = penial filament.

[5] FLMNH catalog 279921, collected by FGT on 8/15/2000 from Bradford Creek at Martin Road, 2 miles south of Madison, AL.

[6] FLMNH 279628, collected by FGT on 8/16/2000 from Round Island Creek at County Road 25, 3 miles west of Jones Crossroads, AL.  Haggerty & Garner [7] were not able to confirm this record in their exhaustive survey of 2008, however.

[7] Haggerty, T.M. & J.T. Garner (2008)  Distribution of the armored snail (Marstonia pachyta) and slender Campeloma (Campeloma decampi) in Limestone, Piney, and Round Island Creeks, Alabama.  Southeastern Naturalist 7: 729 – 736.

[8] And in fact, the entire Flint River (AL) catalog at the FLMNH is a disappointment.  Just N = 50 freshwater gastropod records total from all collectors, the 33 lots not collected by Thompson undated and obviously ancient.

[9] Thompson, F.G. (2005)  Two new species of hydrobiid snails of the genus Marstonia from Alabama and Georgia.  The Veliger 47: 175 – 182.

[10] Yes.

[11] Above, Marstonia pachyta penis modified from Thompson [2] figure 13C and 13D.  Below, Marstonia angulobasis penis from Thompson [9] figure 18a and 18b. Dorsal on left, ventral on right. Tg = terminal gland, Vg = ventral gland, P = penial filament.

[12] For more on the subspecies concept as applied by the FWGNA Project, see:

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

[13] For more about that single, enigmatic SNHTHICACBW shell from Kentucky, see:

  • Is Marstonia ozarkensis extinct? [16Mar20]