Dr. Rob Dillon, Coordinator

Tuesday, September 19, 2023

Is Marstonia olivacea extinct?

Questions regarding the habitat and range of the hydrobiid snail known today as Marstonia olivacea have always taken precedence over any other aspect of its biology.  Originally described in the genus Amnicola by Henry Pilsbry in the February 1895 issue of The Nautilus [1], the name had already appeared in that journal twice previously – first in March of 1894 [2], then again in December [3].

Both anticipatory articles were contributed by Prof. H.E. Sargent of Woodville, AL, and both focused on habitat.  In the March article, “Shell collecting in Northern Alabama,” Professor Sargent observed:

“Huntsville, Alabama, is a somewhat exceptional southern city in that it has an abundant supply of pure spring water bursting forth from its very foundations.  This spring of sparkling lime water, beside supplying the city mains, affords a constant stream several feet in width with several inches in depth go to waste. […] The upper surfaces of the rocks were found to be covered with a species of Amnicola which the Editor … proposes the name of Amnicola olivacea Pils.”

And in a little “Notes and News” item tacked onto the end of the December 1894 issue of The Nautilus, the good professor added,

“AMNICOLA OLIVACEA PILS. – In  April, I visited the original locality (Huntsville, Ala.) and was surprised to find this species in vast numbers.  The stream has a mud bottom which is much indented with cow tracks.  In these the Amnicola had congregated – not as a layer on the surface, but as a solid mass. […] The stream receives some of the city sewerage, so it is probably a good feeding-ground.”

Prof. Sargent’s December remark about “sewerage” in Huntsville’s Big Spring Creek is telling.  We ourselves first visited that unfortunate little body of water in our essay of [15Apr20], questing for Isaac Lea’s Melania perstriata, and gave it another nod in last month’s essay [15Aug23], searching for the illusive Somatogyrus currierianus.  The last time I visited that “marvel to Indian and frontiersmen alike,” I couldn’t even find a Physa.  I have nevertheless marked the Huntsville Big Spring as HV on the map below.

But returning to the thread of our story.  Henry Pilsbry did not apparently find space to wedge his formal description of Amnicola olivacea until the fifth article of the issue he published in February 1895.  And when it appeared it was maddeningly brief and spare, unfigured, and absent any anatomical observations whatsoever [4].  The two shells that he measured were unusually large by hydrobiid standards, however, both “Alt 4.2 mm,” and slender “being of more elongated contour than any other Northern forms except Amnicola lustrica.”  Those observations plus the type locality (“Huntsville, Ala., collected by Prof. H. E. Sargent”) were sufficient to allow subsequent authors to establish the identity of Pilsbry’s taxon.

The first among those subsequent authors seems to have been my hero Calvin Goodrich [5], who wrote in 1944, “This species is somewhat common in streams and springs in and around Huntsville, Madison County, Alabama, drained by the Tennessee River.  Specimens taken by Smith in the Coosa, Minnesota Bend, Etowah County, Alabama [6], have been identified as olivacea.”  This strongly implies that Goodrich was aware of populations of Pilsbry’s A. olivacea at other localities beyond Huntsville’s Big Spring.  The four lots of Marstonia olivacea held in the UMMZ collection today, however, all give locality as either “Huntsville” or “Huntsville Spring” [7].

M. olivacea [12]: lectotype, Hershler, UF279638

But Goodrich was a pleurocerid guy, not a hydrobiid guy.  It was Fred Thompson who first stepped forward to examine Pilsbry’s Amnicola olivacea with a critical eye, in his landmark monograph of 1977 [8].  As my longsuffering readership will remember from last fall [4Oct22], it was Thompson who first elevated F. C. Baker’s [9] nomen Marstonia to the level of a full genus, recognizing as he did eight species in it: Pilsbry’s well-known lustrica, Pilsbry’s obscure olivacea, and six species of his own.

Thompson wrote, “Apparently this species (M. olivacea) was confined to Big Spring Creek in the historic heart of Huntsville.”  And he continued, “This snail is probably extinct.  The creek is badly polluted and has been channelized for most of its course.  No specimens were found by the author during two visits to Big Spring Creek during 1973.”  He went on to examine the paratype lot (N = 456 specimens!) in the ANSP, valiantly attempting “to extract and relax dried bodies,” failing.  He selected the shell figured above as a lectotype.  And regarding its morphology, Thompson observed, “If M. olivacea was from a more northern locality, I would be tempted to consider it a synonym of the highly variable M. lustrica.”  He concluded, “This species’ status remains uncertain.”

My longsuffering readership will also remember from last fall [4Oct22] that Marstonia was briefly synonymized under the genus Pyrgulopsis in 1987 by the dynamic duo of Hershler and Thompson, only to be resurrected again in 2002 [10].  In the interim was published Bob Hershler’s masterful 1994 monograph [11] treating Pilsbry’s olivacea as an “Eastern American Species” in the (temporarily very large) genus Pyrgulopsis.

My Buddy Bob’s scanning electron micrograph of the shell of a young “Pyrgulopsis” olivacea [12] is reproduced middle above.  Bob was also apparently able to rehydrate soft tissues from inside some of Pilsbry’s dried shells, contributing a figure of the radula and a four-line description of the penial morphology.  Hershler left the penis unfigured, alas, and only compared it to other species in broad outline [13].  He concluded, briefly, “This snail resembles widely disjunct P. lustrica in shape of shell and penis, but differs in having strong spiral lines on the teleoconch.”

Hershler quoted Thompson’s understanding of the distribution of P. olivacea, minus any qualification whatsoever, “Known only from type locality, where it is now extinct.”  And that would seem to be the end of this month’s lesson.  Perhaps class will be dismissed early today?  No such luck.

The Florida Museum of Natural History in Gainesville is a marvelous facility, home to a large and well-curated collection extending well beyond regional importance.  The review I posted on [22May19] ranked the FLMNH as #5 in the nation by its freshwater gastropod holdings.  I’d like to call it a beacon on a hill, a guidepost toward which other states and state universities might sail.  But alas, the tide has turned, and the winds have blown ill for a hundred years.  We malacologists of these latter days must give thanks for the few scattered beacons we have, as we strain to navigate by their flickering lights.

So it was that on Monday morning, 10Jan22 I found myself sitting at a metal table in the FLMNH collections, running my fingers through Fred Thompson’s hydrobioid collections from North Alabama, pondering weak and weary, over many a quaint and curious lot of freshwater gastropods.  And my eye happened to fall on lot UF279638, collected by FGT from “Madison Co: Huntsville Blue Springs” (site BA) on 17Aug2000 [14].  That lot of dry shells, indistinguishable to my eye from common Marstonia lustrica, collected from a large spring on private property 5 miles East of Huntsville, had been identified by Fred Thompson himself as Marstonia olivaceaMarstonia olivacea is not extinct.

And that was not the last, nor the greatest revelation of the morning.  The FLMNH collection also held, upon further inspection, a lot UF279620, collected by FGT from Limestone Creek, about 20 miles west of Huntsville, on 16Aug2000, the previous day.  See map point LC above [15].  That lot, comprising a couple dozen specimens in 75% ethanol, was curated into the collection as “Pyrgulopsis n. sp.”  They were absolutely indistinguishable from lot UF279638.

UF279620, from Site LC

If Marstonia olivacea ranges 5 miles East of Huntsville, and 20 miles West of Huntsville, might it also range 60 miles East of Huntsville?  Begging the indulgence of my readership, allow me to step back 46 years, and eight paragraphs, and get a fresh start into this entire story.

Fred Thompson recognized eight species in his newly elevated genus Marstonia in 1977: lustrica, olivacea, agarhecta (which he himself had described in 1969) and five brand new ones.  On page 123 of his monograph, he opined that M. olivacea was endemic to Huntsville and probably extinct.  But two pages earlier he had newly described Marstonia ogmorhaphe [16] from Owen Springs, just over the Tennessee line 60 miles NE of Huntsville (map OS).  It was initially “known only from its type locality,” but a second population of M. ogmorhaphe was subsequently discovered 5 miles west, in the Blue Spring [17] of Marion County (map BT).

Thompson made no effort to distinguish his new M. ogmorhaphe from the older M. olivacea.  Quoting him verbatim from page 120, “Marstonia ogmorhaphe is distinguished from all other species of Marstonia by (1) its large size (4 – 5 mm), and (2) its large number of whorls (5.2 – 5.8).”  On page 123, Thompson went on to give the length of the holotype of M. olivacea as 4.35 mm, and number of whorls as 5.4.

Owen Springs, courtesy of Alan Cressler

Seventeen years later came Bob Hershler’s big Pyrgulopsis monograph [11], and the formal listing of Pyrgulopsis (= Marstonia) ogmorhaphe as “endangered” by the US Fish and Wildlife Service [18].  My buddy Bob’s treatment of this suddenly noble gastropod, now styled the “Royal Snail,” was brief.  Both he and Thompson noted the similarity between olivacea and lustrica, and both he and Thompson noted the similarity between ogmorhaphe and lustrica, but neither he nor Thompson thought to compare olivacea to ogmorhaphe.

So, in summary.  My biological intuition suggests to me that Marstonia ogmorhaphe (Thompson 1977) is a junior synonym of Marstonia olivacea (Pilsbry 1895).  The dispersal capabilities of freshwater gastropods are much greater, and their specific ranges much wider than they are commonly given credit for, even among professionals.  The (effectively indistinguishable) Marstonia lustrica ranges across 12 states and 3 Canadian provinces and must have spread across most of this vast territory since the Pleistocene [19].  I cannot see why populations of a second very similar species, best identified as Marstonia olivacea, could not spread 60 miles from North Alabama to East Tennessee.  And I cannot find a single speck of evidence suggesting that any reproductive isolation may have evolved subsequently.


[1] Pilsbry, H.A. (1895) New American fresh-water mollusks.  Nautilus 8: 114 – 116.

[2] Sargent, H.E. (1894) Shell collecting in Northern Alabama.  Nautilus 7: 121 – 122.

[3] Sargent, H.E. (1894) Amnicola olivacea Pils.  Nautilus 8: 95 – 96.

[4] My faithful readership will be familiar with the eccentricities of the character of The Ancient Emperor, Dr. Henry A. Pilsbry.  In his capacities as Curator of Mollusks at The Academy of Natural Sciences of Philadelphia and Editor of The Nautilus, he cast a giant shadow across the face of American malacology for 70 years.  You are also aware that Pilsbry was simultaneously fastidious and sloppy, capable of precise, detailed, and critical observations of parrot feathers in a pirate attack.  For more, see:

  • The Emperor Speaks [5Dec20]
  • The Emperor, the Non-child, and the Not-short-duct [9Feb21]
  • Dr. Henry A. Pilsbry was a Jackass [26Jan21].

[5] Goodrich, C. (1944) Certain operculates of the Coosa River.  Nautilus 58: 1 – 10.

[6] The “specimens taken by Smith in the Coosa” were described as Marstonia hershleri by

  • Thompson, F. G. (1995) A new freshwater snail from the Coosa River, Alabama (Gastropoda: Prosobranchia: Hydrobiidae).  Proc. Biol. Soc. Washington 108: 502 – 507.

[7] All of these lots are undated, alas.  They are catalogue numbers 120720 of H.E. Sargent, 143685 of H.H. Smith, 237147 of P.L. Marsh, and 1516 of an unknown collector.

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

[9] Baker, F. C. (1926) Nomenclatural notes on American fresh water Mollusca. Transactions of the Wisconsin Academy of Sciences, Arts, and Letters 22:193-205.

[10] Thompson, F. G. & R. Hershler (2002)  Two genera of North American freshwater snails: Marstonia Baker, 1926, resurrected to generic status, and Floridobia, new genus (Prosobranchia: Hydrobiidae: Nymphophilinae).  The Veliger 45: 269 - 271.

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

[12] The standard lengths of these three figured shells are 4.3 mm for Thompson’s [8] lectotype, 4.5 mm for my selection from lot UF279638, and just 3.4 mm for Hershler’s [11] youngish specimen.  My Buddy Bob had a longtime romance with scanning electron microscopy, and tended to select smaller shells for his figures, which are easier.

[13] In fairness to Bob Hershler, the morphology of dried and rehydrated soft tissues cannot be compared to anything other than other dried and rehydrated soft tissues.  I would have loved to see a comparison of the penial morphology of M. olivacea, M. lustrica and M. ogmorhaphe, but to do so Bob would have had to desiccate a bunch of fresh lustrica or ogmorhaphe to brittle dryness first.

[14] There is an error in the lat/long coordinates for UF279638 as entered into the FLMNH database, which may have contributed to the obscurity of this record.  The correct lat/long coordinates for the Blue Spring of Madison County, Alabama, are 34.7080, -86.5123.  They are not “31.66361, -85.50667.”  Those are the coordinates of the Blue Springs of Barbour County, AL.

[15] This spot is way downstream near the mouth of Limestone Creek, underneath the I-565 spur, at 34.6317, -86.8667.

[16] Thompson spelled his new species “ogmorphaphe” at the heading of his description  and “ogmorhapha” in his table of contents, but “ogmorhaphe” enough times otherwise to make the one-pee-final-e spelling stick.

[17]  To be very clear.  The Blue Spring of Marion County, Tennessee (35.0816, -85.6325) is different from both the Blue Spring of Madison County, Alabama (34.7080, -86.5123) and the Blue Springs of Barbour County, Alabama (31.6636, -85.5067).

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

[19] The hypothesis I am offering here is now fair game for testing with a gene tree.  But if you are a bright young graduate student looking for thesis ideas, please first read Essay  the paper by Tom Coote [20].  Then read this essay, and the essays linked from it:

  • Mitochondrial heterogeneity in Marstonia lustrica [3Aug20]

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

Tuesday, August 15, 2023

The Union in Tennessee! For lithoglyphid hydrobioids, that is.

In last month’s episode [11July23], we marched south from Tennessee into Alabama with Gen. Ormsby Mitchel, the First Michigan Engineers and Mechanics Regiment, and Dr. W. H. DeCamp.  Capturing Huntsville on the morning of April 10, 1862, Mitchel’s forces moved rapidly both East and West to secure the vital Memphis & Charleston Railroad, by the end of the summer controlling 100 miles of riverbank on the north side of the Tennessee River.  And somewhere in the vicinity of Huntsville, sometime during that long and exciting summer of 1862, Dr. William Henry DeCamp, Surgeon US Army, collected a small sample of small lithoglyphid hydrobioids that turned out to be the first Somatogyrus described from the drainage of The Tennessee River, Somatogyrus currierianus (Lea 1863) [1, 2].

North Alabama campaign [3]

Last month we also reviewed what is known about the distribution of Somatogyrus elsewhere throughout the Tennessee drainage, both historic and modern.  East Tennessee populations have typically been identified with Tryon’s (1865) nomina S. parvulus and S. aureus [4], the former name prevailing in the tributary rivers above Knoxville, the latter further downstream in Knoxville and vicinity.  The Hiwassee hosts a well-documented population of Somatogyrus apparently trans-Appalachian in origin, and the little snails also pop up occasionally in TN-DEC macrobenthic samples collected from Chickamauga Creek near Chattanooga as well.

Middle Tennessee populations are less well-known, and if identified at all, are usually assigned the name Somatogyrus depressa, which Tryon (1862) used to describe populations in the Mississippi River at Davenport, Iowa [5].  These include a large population inhabiting the Duck River and a small population in the Harpeth River, a tributary of The Cumberland west of Nashville [6].

Between the East Tennessee populations identified as  S. parvulus/aureus and the Middle Tennessee populations identified as S. depressa are Dr. W. H. DeCamp’s old stomping grounds in North Alabama.  And last month we concluded that the key to understanding the entire, far-flung Somatogyrus fauna of the Tennessee River system is to understand that little sample of little snails Dr. DeCamp collected at “Huntsville” in 1862, sent to Isaac Lea and described as currieriana the following year [1].  Can Dr. DeCamp’s type population be found again?

That question weighed heavily on my mind as I tipped my hat to the Missus and boarded a westbound train for Alabama in August of 2021 [7].  The Huntsville Somatogyrus problem seemed closely analogous to that with which I had wrestled in the spring of 2020, searching for the type population of Melania perstriata, also described by Isaac Lea from Huntsville but in 1853, before the war [15Apr20].  The field notebook under my arm bulged with many water-stained pages of observations about the malacologically rich area toward which the Memphis & Charleston Railroad was bearing me that morning.

The city of Huntsville, I knew, had built up around a lovely, high-volume spring that was almost certainly the type locality of Melania perstriata, and which was quite likely the type locality of S. currierianus as well.  But I was also aware that in modern times the spring and its run have been channeled in concrete bulkheads through a formal midtown park and rendered essentially devoid of macrobenthos.  I didn’t see any Somatogyrus there in 2020, when I wasn’t seeing any Pleurocera (“Melania”) perstriata.

What to do?  It seemed to me that my best option would be to draw a series of concentric circles on my map around the Big Spring of Huntsville and try to find the Somatogyrus population next-closest.  So, upon arrival at the Huntsville Depot the next morning, I brushed the cinders from my frock coat, hired a mule-drawn hack at the livery, and set off down the Cottonville Pike for the Flint River about 10 miles distant.  This, I knew from experience, was the first body of water my mules would kick into substantial enough to host a population of Somatogyrus, travelling east.  And soon a second challenge, beyond the 150 years of landscape evolution boggling my eyes as we clip-clopped by the Starbucks, presented itself.

The Flint River Somatogyrus population is weird looking.  I figured a typical specimen in the Cherrytree montage I published in my [3Nov22] essay on Marstonia pachyta and figured a life-sized image of that same specimen again last month [11July23], and I’m going to show you a third time this month, marked Fl in the figure below.  The Flint River population seems to reach adulthood at an exceptionally small size, no more than maybe 2-3 mm shell length.  The shells they bear are also unusually light and – here’s the big shocker – typically show at least a little bit of umbilicus.  That’s right.  Flint River Somatogyrus look like Clappia.

I also figured the type of Lea’s S. currierianus last month, and I apologize about the quality of that image; the original picture was only about 5 mm in the monograph.  But Lea’s figure showed a much more robustly shelled snail, no umbilicus in evidence, as is typical for the genus.  Standing ankle-deep in the Flint River in the summer of 2021, holding the reins of a brace of wet mules in my left hand, I simply could not bring myself to designate the weird-looking little Somatogyrus crawling around at the bottom of the sawed-off trashcan I was holding in my right, as topotypic currierianus.

So, I re-mounted my asinine conveyance, and with a light touch of the whip continued eastward another 10 dusty miles or so beyond the Flint, to the sparkling waters of the Paint Rock River.  And there I found a somewhat larger-bodied and heavier-shelled population of Somatogyrus, a typical specimen from which is labeled PR above.  The Paint Rock population bears shells that are not umbilicate, and look fairly typical for the genus, and I thought at the time, might suit as modern topotypes.  Storing a sample in my watch pocket, I turned my wagon back into the setting sun, and returned to Huntsville for the night.

The next morning, I bought a fresh ticket at the station and boarded a westbound for Decatur and Tuscumbia.  And I resolved, as I did, to jump off at the first trestle [8], crossing the Limestone Creek about 15 miles west of the city.  She was making 30 miles an hour as we approached the bridge, but the drop was no more than 12 -15 feet, so I landed with the loss of no more than my hat, and vision in my left eye.

The shells borne by the Somatogyrus I plucked from Limestone Creek looked fairly typical, at least in the downstream precincts of Mooresville, at the railroad crossing.  See figure Lid above.  But as I made my way upstream, a new and intriguing phenomenon unfolded before my eyes.  The shells of the Limestone Creek Somatogyrus population began to open an umbilicus.  The photo below compares a shell collected downstream, 1 mile NE of Mooresville (Lid), to a shell collected about 12 miles upstream, at Capshaw (Liu).  Although the former is quite typical for Somatogyrus populations throughout the Tennessee drainage, the latter would conventionally be identified as Clappia.

And then it dawned upon me that I had seen this same phenomenon in the Powell River ten years previous – a Clappia population upstream blending into a Somatogyrus population downstream [9].  Both upstream populations seem to reach maturity at a smaller size, bear lighter shells, and prefer a substrate of woody debris on the margins.  The downstream populations are larger, more robustly shelled, and inhabit rocks midstream.  The parallel nature of this phenomenon, as it apparently manifests itself in both East Tennessee and North Alabama, suggested to me cryptic phenotypic plasticity of a high and aggravated nature.

All these thoughts tumbled through my mind as I walked the dusty road west toward Piney Creek, no more than a mile beyond Mooresville.  And what I found in Piney Creek reminded me very much of what I had seen in the Flint River on the previous day.  The Somatogyrus population of Piney Creek was exceptionally small-bodied, lightly shelled, and umbilicate, animals reaching adulthood not much more than 2 mm shell length, as depicted in Figure Pi above.

That evening I camped under the Decatur bridge, cooked a cup of chicory coffee in a tin can, and watched the Tennessee River flow by.  Actually, the river didn’t flow any more than I did.  Although this stretch of river would have been wild and free in 1862, the TVA closed Wheeler Dam about 30 miles downstream in 1936, backing the Tennessee River up almost 60 miles to Huntsville.  And all that met my eye that evening at the Decatur Bridge was slackwater swamp.

How many molluscan lives were lost as those flat, scummy waters inundated the historic Muscle Shoals between Florence and Decatur, I wondered to myself, as the sun set.  How many millions of unionid mussels, how many billions of pleurocerid snails?  Throughout the nineteenth century and into the twentieth, scores of Melania, Anculosa, Leptoxis, Pleurocera, Trypanostoma, Goniobasis, Lithasia, Angitrema, Strephobasis, and Eurycaelon were described and re-described from the rivers and streams around Muscle Shoals [10].  The pleurocerid populations inhabiting the roiling waters of that mighty river, bearing heavier, more robust shells, were typically assigned Latin nomina different from more lightly shelled populations inhabiting the gentler tributaries.

The Pleurocera canaliculata population inhabiting the main Tennessee River here at Decatur, I knew, extends up nearby Limestone Creek, where they were described as Melania pyrenella by Conrad in 1834. Historic nomina such as Conrad’s pyrenella, although now relegated to synonymy [11], nevertheless have demonstrable utility to describe morphological forms not apparently correlated with reproductive isolation, possibly ecophenotypic in origin.  We have suggested that such nomina, especially those around which some published literature has subsequently developed, be preserved at the subspecific level by virtue of their indexing function.

Similarly.  In 1906 Bryant Walker described seven species of Somatogyrus from the Muscle Shoals area, all of which bore robust shells, apparently adapted to large rivers with strong current [12].  Figure Sh above shows a typical specimen of Walker’s S. tennesseensis  from the Florida State Museum (cat. 83116), collected at “Shoals Creek near mouth with Tennessee River” date unknown.  That big-river shell morphology seems to match the image of Lea’s currierianus (see last month) better than any of the populations inhabiting the smaller tributary waters today.  But alas, the Somatogyrus of Muscle Shoals were buried under the slackwater with the unionids and the pleurocerids in 1936.  Gone With The Swamp.

Then by analogy with the better studied pleurocerids, we suggest that the following nomina are junior synonyms of Somatogyrus currierianus (Lea 1863):  aureus Tryon 1865, excavatus Walker 1906, humerosus Walker 1906, parvulus Tryon 1865, quadratus Walker 1906, sargenti Pilsbry 1895, strengi Pilsbry & Walker 1906, substriatus Walker 1906, and tennesseensis Walker 1906 [4, 12, 14].

And extending the analogy further.  The evidence reviewed above suggests that the populations described by Bryant Walker in 1904 as Somatogyrus umbilicata [15], separated by him into a new genus Clappia in 1909 [16], are lightly shelled upstream variants of Somatogyrus currierianus.  We therefore propose that Walker’s nomen umbilicata be lowered to subspecific status under Lea’s S. currierianus.

And in conclusion, we take this opportunity to remind our readership once again that the FWGNA has adopted the definition of the word “subspecies” standard since the Modern Synthesis, “populations of the same species in different geographic locations, with one or more distinguishing traits” [17].  Although there certainly may be some heritable basis for the umbilicus demonstrated by the shells of some small river Somatogyrus populations, and indeed for all the remarkable shell variety of all the remarkable freshwater malacofauna of North Alabama, ecophenotypic origins are at least equally likely.


[1] Lea, I (1863) Descriptions of fourteen new species of Melanidae and one Paludina.  Proceedings of the Academy of Natural Sciences of Philadelphia 4: 154 – 156.

[2] Lea, I (1866)  New Unionidae, Melanidae, etc., chiefly of the United States.  Journal of the Academy of Natural Sciences of Philadelphia Series 2, 6: 113 – 187.

[3] This is a small detail from a map of Alabama and Mississippi published by the United States Coast Survey in 1865.  Retrieved from the Library of Congress here: https://www.loc.gov/resource/g3980.cw0259500/

I added the colored marks and notes.

[4] Tryon, G. W. Jr. (1865)   Descriptions of new species of Amnicola, Pomatiopsis, Somatogyrus, Gabbia, Hydrobia and Rissoa.  American Journal of Conchology 1: 219-222, pl 22, figs 5-13.

[5] Tryon, G. W. (1862)  Notes on American fresh water shells, with descriptions of two new species.  Proceedings of the Academy of Natural Sciences of Philadelphia 14: 451 – 452.  I really think that Somatogyrus populations of the main Mississippi River are today best identified as Somatogyrus integra (Say 1829).

[6] Here’s a download of all 2,152 the Somatogyrus occurrences in the GBIF, as of 17Oct22: GBIF.org (17 October 2022) GBIF Occurrence Download https://doi.org/10.15468/dl.nv3tjh

[7] No, I drove I-20 to I-75 like everybody else these days and spent two hours in the Atlanta traffic.

[8] Actually, a westbound train from Huntsville will cross Indian Ck, Bradley Ck, and Beaverdam Ck before arriving at Limestone Ck.  None of these smaller streams seems to host a Somatogyrus population today.

[9] For a review of Bryant Walker’s contributions to our understanding of the hydrobioid genera Somatogyrus and Clappia, together with my own personal observations from East Tennessee on these enigmatic taxa, see:

  • Bryant Walker’s Sense of Fairness [5Nov12]
  • On getting Clappia in Tennessee [3Dec12]

[10] The actual count of pleurocerid species inhabiting the waters of North Alabama today totals ten: Leptoxis praerosa, L. crassa, Lithasia armigera, L. verrucosa, Pleurocera canaliculata (2ssp), P. clavaeformis (2 ssp.), P. laqueata, P. nassula, P. simplex, P. troostiana (3 ssp).

[11] Dillon, R. T., S. J. Jacquemin & M. Pyron (2013)  Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117-127.  [PDF]  For a discussion of these important results, see:

  • Pleurocera acuta is Pleurocera canaliculata [3June13]
  • Pleurocera canaliculata and the process of scientific discovery [18June13]

[12] Walker. B. (1906)  New and little known species of Amnicolidae.  Nautilus 19: 97-100, 114-117.  In this paper Walker (solo) described six Somatogyrus from Shoal Creek and the main Tennessee River around Florence, Alabama: substriatus, humerosus, quadratus, excavatus, tennesseenis, and biangulatus [13].  He also described strengi from the same area, which he credited to “Pilsbry & Walker.”

[13] I think that the populations Walker described as Somatogyrus biangulatus in 1906 may indeed have been biologically distinct, and now extinct.

[14] Pilsbry, H.A. (1895) New forms of American shells. Nautilus 8(9): 102.

[15] Walker, B. (1904)  New species of Somatogyrus. Nautilus 17: 133 - 142.

[16] Walker, B. (1909)  New Amnicolidae from Alabama. Nautilus 22: 85 - 90.

[17] For an elaboration of the concept, see:

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

Tuesday, July 11, 2023

Somatogyrus and Yankees in North Alabama

Early in the morning of April 10, 1862, eight thousand Federal troops under the command of Gen. Ormsby Mitchel captured the sleeping town of Huntsville, Alabama, without firing a shot [1].  Knowing that both of the main armies were licking their wounds from the Battle of Shiloh about 120 miles west on the banks of the Tennessee three days earlier, Mitchel seized the opportunity for a lightning strike south from Shelbyville.  By the end of April, he controlled 80 miles of the Memphis & Charleston Railroad from Bridgeport to Decatur, writing to Secretary of the Army Edwin Stanton, “All of Alabama north of the Tennessee River floats no flag but that of the Union.”  Mitchel’s Division held North Alabama for four months, withdrawing in reaction to Braxton Bragg’s thrust north from Chattanooga in August [2].  By September they were home on the banks of the Ohio in Louisville.

Dr. DeCamp at the Elk River [1]

Attached to Mitchel’s command was the First Michigan Engineers and Mechanics Regiment, numbering among its ranks a Grand Rapids surgeon named Dr. William Henry DeCamp (1825-1898) [3].  DeCamp had been born in upstate New York and moved to Grand Rapids in 1854, where he set up a medical practice.  He was one of the founders of the “Grand Rapids Lyceum of Natural History,” and had more than a hobbyist’s interest in shells.  And so it was accomplished that sometime between April and August of 1862, somewhere in the vicinity of Huntsville, Alabama, Dr. W. H. DeCamp, Surgeon US Army, stooped to capture a small detachment of rebel freshwater gastropods.

DeCamp detailed his prisoners back behind the lines to his friend and fellow member of the Grand Rapids Lyceum, Alfred Osgood Currier (1817 – 1881), who forwarded a subset onward to Dr. Isaac Lea in Philadelphia [4].  And if all of this sounds vaguely familiar to you, your memory is to be commended.  For back on [4Aug19] I spun a very similar yarn about Capt. S. S. Lyon, who arrived at Cumberland Gap this very same summer of 1862, as uninvited as Dr. DeCamp, and stooped to capture a regiment of rebel pleurocerids from the ice cold waters of East Tennessee as boldly as Dr. DeCamp in North Alabama.  And Capt. Lyon sent his prisoners to Dr. Lea as well.

So in my essay of [4Aug19], I wrote, “In May of 1863, a scant nine months later, Lea described four new species of Goniobasis” sent to him by Capt. Lyon from Gap Springs [5].  Actually, to be quite precise, Lea published brief, Latinate descriptions of 15ish [6] species in that Mayish [7] paper, including six captured by “Capt. S. S. Lyon, U.S. Army,” six captured by “Dr. Wm. H. DeCamp M.D., Surgeon US Army,” and three arrested by civilians working well behind the lines.  The six DeCamp species included three pleurocerids from the Falls of the Ohio in Louisville, two pleurocerids from North Alabama, and Amnicola currieriana, from “Huntsville.”  Lea’s currieriana was the first specific nomen unambiguously ascribed to what we today recognize as the hydrobioid genus Somatogyrus in the drainages of The Tennessee.

Lea published a more complete description of A. currieriana in 1866, together with a figure [8].  “This little species differs from all other Amnicolae which I have seen in the broad deposit of the columella, particularly in the middle, where it covers the umbilicus.”  And indeed the 1:1 figure on Lea’s Plate 24 does show a very robust, solid little shell, no umbilicus in evidence.  Compare the grayscale figure at lower right below to typical shells from five other Somatogyrus populations more recently sampled from North Alabama.  We’ll have more to say about those five modern populations next month.

1.5 x life size.
It never ceases to amaze me how the War for Southern Independence prompted such a blossoming of interest in little-brown crap snails throughout Yankeedom 1861 – 1865.  Every gentleman of means north of the Mason-Dixon line became a Malacologist, a Quaker, or both [9].  In September of 1862, just 8 – 10 months prior to Isaac Lea’s description of A. currieriana, his younger colleague George W. Tryon had published a description of a very similar Amnicola depressa from the Mississippi River at Davenport [10].  And in February of 1863, three or maybe five months prior, Theodore Gill (also of Philadelphia) had selected George Tryon’s depressus, as the type of his new genus Somatogyrus [11].

Tryon added two fresh species to the genus in 1865 [12]: Somatogyrus parvulus from the Powell River (a tributary of the Tennessee above Knoxville) and S. aureus “received from Mr. Lea several years ago” from somewhere in the “Tennessee River.”  And we were off to the races.  Between 1904 and 1915 Bryant Walker [13] described 22 new species of Somatogyrus [14], and other authors shoveled on as well, to the point that Burch’s 1982 Bible [15] listed 35 species of the genus, including 9 nominal species described from North Alabama alone, all utterly indistinguishable.  And alas, no lithoglyphid-Goodrich [16] has subsequently arisen to clean up the taxonomic mess.

All 35 species were described on the basis of qualitative differences in shell morphology alone.  For example, the first species described by Walker in his 1904 paper was S. hinkleyi from the Coosa River (of the Mobile Basin) at Wetumpka, AL.  Walker wrote, “It differs from all the known species in the elevated spire and conical form excepting S. pennsylvanicus and virginicus herein described, but those species are much smaller and decidedly different in contour.”  Somatogyrus hinkleyi is figured (1) and (2) on Walker’s plate below, pennsylvanicus is (15) and (16), and virginicus is figured (17), (18), and (19).  You be the judge.

From Walker (1904)

But let me back up and edit my opinion that all 35 nominal species of Somatogyrus are “utterly indistinguishable” just slightly [18].  One of the 11 species of Somatogyrus that Walker described in 1904, S. umbilicatus was different looking.  Collected from the Coosa River at Wetumpka, S. umbilicus was so lightly shelled that it had an umbilicus, as its name telegraphs so plainly.  My readership of long memory and narrow interest may remember that Bryant Walker went on to propose a new genus, Clappia, to hold his nomen umbilicatus in 1909 [19].

And might some of you also remember that in 2012 I reported discovering two populations of Clappia in East Tennessee – one in the Sequatchie River, and the other way up in the headwaters of the Powell in SW Virginia [19]?  You can be forgiven if your memory fails you now.  But hold those tidbits about Clappia tight till next month.  You’re going to need them.

I suppose I might also expand my observation above that no lithoglyphid-Goodrich has risen to clean up the Somatogyrus mess in these latter days.  Fred Thompson did publish a 33-page monograph on the group in 1984 [20], selecting one representative from each of the five lithoglyphine genera he recognized in North America (Gillia, Fluminicola, Somatogyrus, Clappia, and Lepyrium) for detailed anatomical review.  But here is a telling quote from the second paragraph of Thompson’s introduction:

“This study stems from two independent investigations.  The first was an attempt to determine species-group characteristics within Somatogyrus, a genus containing many species (Burch & Tottenham 1980).  The study was tabled temporarily because very little anatomical diversity was discovered among the species examined.  Independently I examined the anatomy of Lepyrium showalteri (Lea), a snail previously placed in a monotypic family of uncertain affinity.  Its soft anatomy was found to be hardly distinguishable from that of Somatogyrus.”

Thompson never picked his first “independent investigation” back up off the table.  Apparently as far as he could ever tell, all 35 of the nominal Somatogyrus species catalogued in the Burch Bible were as utterly indistinguishable anatomically as they were shell morphologically.  In fact, the only soft-part difference of any sort he reported across all five lithoglyphine genera was the presence of a papilla on the penis of Gillia and Fluminicola.  Even the penial morphology of Somatogyrus, Clappia, and Lepyrium is indistinguishable, even by the most discerning splitter – just a simple, pointy hose.

Had Thompson understood the hydrobiids as Goodrich understood the pleurocerids, at this point he would have synonymized the entire 35-member crap-pot of Somatogyrus down an order of magnitude to three species and a subspecies.  Instead, he added an appendix of his 1984 paper for the description of yet another utterly indistinguishable species of Somatogyrus from Georgia, S. rheophilus.  Fred Thompson was no Calvin Goodrich.  And it is through the dusky twilight of Walker and Burch that we still walk to this day.

From Fig 43 of Thompson [20]

One might imagine, from all the taxonomic excitement generated by Bryant Walker, his forebears, contemporaries and successors, that populations of Somatogyrus must have been common throughout the Tennessee River basin in the early 20th century.  That is certainly not true today, and I’m not sure it was true even back then.  Pilsbry & Rhoads (1896) reported a Somatogyrus population in the “Nolachucky River near Greeneville” which I have not been able to verify [21].  Nor can I confirm the populations that Walker (1904) reported in the Tennessee River at Knoxville, or in its tributary the Holston.

But here is an important point.  The five major tributaries of the Tennessee River above Knoxville, from north to south, are the Powell, the Clinch, the Holston, the Nolichucky, and the French Broad.  Tryon described his (1865) S. parvulus from the Powell, where populations still hang on today.  Two generations later, Pilsbry & Rhoads (1896) and Walker (1904) identified populations collected from the Holston 20 miles south of the Powell and the Nolichucky 20 miles south of the Holston as Somatogyrus aureus.  Between Tryon and Pilsbry came the immortal team of Dr. James Lewis and Miss Annie E. Law.

Dr. James Lewis (1822 – 1881) was a dentist/conchologist from Mohawk, NY, who was reputed to have one of the greatest private collections of American land and freshwater shells in existence at the time of his death.  According to his obituary in The American Naturalist [22], he “arranged and classified many public collections, among which were the American fresh-water shells in the Smithsonian Institution, the last critical revision of which was made by him.”  Really?  He should be better known today than he is.

Miss Annie Elizabeth Law (1842 – 1889), school teacher and alleged Civil War spy [23], was born in England but spent most of her life in the vicinity of Maryville, Tennessee [24].  “Through Col. W. G. McAdoo, of Knoxville, she was introduced to Dr. James Lewis, of Mohawk, New York, who wished her to collect shells.  She had from childhood a taste for shells, mineralogy, entomology, botany, in fact everything connected with nature,” and so was apparently eager to comply.  Over a period of some two years, Miss Law walked 20 miles of the Holston River “from Little River Shoals to Chota Shoals,” collecting both the bivalves and the gastropods she discovered along the way, posting them to her sponsor in Mohawk, NY.  In his 1871 report of her expedition [25], Lewis observed:

“I have from Miss Law numerous shells identical with Somatogyrus parvulus, Tryon, found, at very low stages of water, in little pools left by the receding water along swift, shallow, gravelly portions of the Holston.  Less abundantly a somewhat larger shell agreeing with S. aureus Tryon.  Also larger shells identical with “Amnicola Currieriana, Lea,” found in still water, along muddy portions of the Holston, near the shore.  They are, without doubt different ages of one species.  Mr. Leas name for the species takes precedence.”

Yes, Dr. James Lewis identified Somatogyrus currierianus (Lea 1863) in East Tennessee.  And he synonymized both parvulus (Tryon 1865) and aureus (Tryon 1865) underneath it.

That brings our essay full circle, back to the exciting summer of 1862, and Dr. W. H. DeCamp standing on the banks of the big-river Tennessee somewhere in the vicinity of Huntsville.  The key to understanding the Somatogyrus of the entire Tennessee River drainage is to understand Somatogyrus currierianus in North Alabama. Next time, a fresh adventure!


[1] I have taken most of the historical narrative in the first two paragraphs above, as well as the interesting figure, were from:

  • Hoffman, M. (2007) My Brave Mechanics: The First Michigan Engineers and their Civil War.  Wayne State University Press, 470 pp.

[2] Mitchel was promoted to command the entire Department of The South, and transferred to Beaufort, SC, where he died almost immediately of Yellow Fever.  Why was Mitchel in Beaufort?  See:

  • The Many Invasions of Hilton Head [16Dec15].

[3] This is the fourth time that the name of Dr. W. H. DeCamp has come up in the 25 year record of this blog.  We focused a great deal of attention on Goniobasis decampii Lea 1863/66 [6] in “A House Divided” [10May20], and on Campeloma decampi (Binney 1865) in “Fun With Campeloma” [7May21].  Lymnaea decampi Streng 1906 also garnered a brief mention in footnote [3] of “Malacological Mysteries I: The type locality of Lymnaea humilis” way back in [25June08].

[4] For a brief biography of the “Nestor of American Naturalists” see:

  • Isaac Lea Drives Me Nuts [5Nov19]

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

[6] Lea apparently intended to include a description of Melania decampii from Huntsville in his paper of Mayish [7] 1863, but that paragraph was omitted.  In his follow-up paper of 1866 [8] he stated that the Latinate description of Melania decampii had been published previously in “Proc. Acad. Nat. Sci., 1863, p. 154” but it was not.  Was Lea’s statement an overt fabrication, or just sloppiness?  Either way, stuff like this drives me nuts.  Absolutely nuts [4].

[7] Lea apparently read his paper in May of 1863, and “May” is printed on the bottom of the published pages, but the front of the published volume says, “June and July, 1863.”

[8]  Lea, Isaac (1866) New Unionidae, Melanidae, etc. chiefly of the United States.  Journal of the Academy of Natural Sciences of Philadelphia (New Series) 6: 113 – 187.

[9] For more about the malacologists of Yankeedom 1861 – 1865, see:

  • Ferrissia fragilis (Tryon 1863) [6Feb19]

[10] Tryon, G. W. (1862)  Notes on American fresh water shells, with descriptions of two new species.  Proceedings of the Academy of Natural Sciences of Philadelphia 14: 451 – 452.  I really think that the Mississippi River Somatogyrus populations are best identified today as Somatogyrus integra (Say 1829).

[11] Gill, T. (1863) Systematic arrangement of the mollusks of the family Viviparidae, and others, inhabiting the United States. Proceedings of the Academy of Natural Sciences of Philadelphia 15: 33 – 40.

[12] Tryon, G. W. Jr. (1865)   Descriptions of new species of Amnicola, Pomatiopsis, Somatogyrus, Gabbia, Hydrobia and Rissoa.  American Journal of Conchology 1: 219-222, pl 22, figs 5-13.

[13] Here’s a brief biography of Michigan’s Father of Malacology:

  • Bryant Walker’s Sense of Fairness [9Nov12]

[14] Bryant Walker’s papers on Somatogyrus:

  • Walker, B. (1904)  New species of Somatogyrus.  Nautilus 17: 133 - 142.
  • Walker. B. (1906)  New and little known species of Amnicolidae.  Nautilus 19: 97-100, 114-117.
  • Walker, B. (1909)  New Amnicolidae from Alabama.  Nautilus 22: 85 - 90. 
  • Walker, B. (1915) Apical characters in Somatogyrus with descriptions of three new species.  The Nautilus 29: 37 - 41, 49 - 53.

[15] 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 a stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

[16] A “lithoglyphid” is a member of the modern family Lithoglyphidae, previously a subfamily of the Hydrobiidae [17], bearing featureless anatomy and shell morphology, characterized by nothing whatsoever.  And Calvin Goodrich was the twentieth-century hero who brought science to the classification of the Pleuroceridae, which was an order of magnitude worse.  For more, see:

  • The Legacy of Calvin Goodrich [23Jan07]

[17] Wilke, Haase, Hershler, Liu, Misof, and Ponder (2013) Pushing short DNA fragments to the limit: Phylogenetic relationships of “hydrobioid” gastropods.  Molec. Phyl. Evol. 66: 715 – 736.  For a review, see:

  • The Classification of the Hydrobioids [18Aug16]

[18] Well, to be fair, Walker described two species of Somatogyrus with distinctive shell morphology: umbilicatus in 1904 and biangulatus in 1906.  The latter seems to have been endemic to the main Tennessee River at Muscle Shoals, and now (I fear) extinct.

[19] See my 2012 series of essays for a study of Bryant Walker, Somatogyrus, Clappia, and the relationships between all three:

  • Bryant Walker’s Sense of Fairness [9Nov12]
  • On Getting Clappia in Tennessee [3Dec12]

[20] Thompson, F.G. (1984) North American freshwater snail genera of the hydrobiid family Lithoglyphinae.  Malacologia 25: 109 – 141.

[21] Pilsbry, H. & Rhoads, S. (1896)  Contributions to the Zoology of Tennessee, Number 4, Mollusca. Proc. Acad. Nat. Sci. Phila. 1896: 487-506.

[22] Call, R.E. (1881) Memoriam of Dr. James Lewis.  The American Naturalist 15: 506-508.

[23] I have not been able to confirm the allegations of spying, and I strongly suspect it was for the Union, but I don’t care, I would have really loved to meet Miss Annie E. Law.  Hell, if I was 120 years younger, I would have proposed.

[24] I have pieced my biographical background on Miss Law from a variety of secondary sources, including Tucker Abbott’s (1973) American Malacologists, The Poppe’s conchology.be website, and Nautilus 40: 132 – 133.

[25] Lewis, J. (1871)  On the shells of the Holston River.  American Journal of Conchology 6: 216-226.

Tuesday, June 6, 2023

The Mystery Snail Color Genetics Project

Who among you, my vast and far-flung readership, has not at least once in your life lingered at the face of a hobbyist aquarium to enjoy a “Mystery Snail?”  Show of hands?  One or two of you in the back?

From Ms. Rachel Voss
OK, a bit of introduction may be helpful before we get down to business this month.  The common name “mystery snail” is today almost universally [1] applied to Pomacea diffusa, the most popular gastropod in the home aquarium worldwide, a (relatively) small South American ampullariid domesticated in the late 1960s [3] for the international pet trade.  Such snails were generally identified as Pomacea bridgesii (Reeve 1856) until around 2007, when a team of our colleagues [4] suggested that the nomen diffusa, proposed as a subspecies of P. bridgesii by the German biologist Werner Blume in 1957 [5], might merit recognition at the full species level.

Although small bodied by the standards of the Ampullariidae, and hence not as voracious of aquarium plants, nor as dangerous as pests upon escape into the wild [6], Pomacea diffusa are still large enough to have a personality, which is, in the eyes of many an adoring enthusiast, charming.  Open my essay of [21Dec17] in a new window for more context, and a bit of additional biological background on mystery snails in the home aquarium.

Some not-insubstantial fraction of the popularity of mystery snails derives from their color polymorphism.  Although I have seen at least 15 – 20 named color varieties on the market, consensus seems to suggest eight distinct phenotypes, some with multiple names.  These are depicted in Ms. Brookana Ashley Patton’s colorful figure below, with a standard name suggested for each: gold, jade, ivory, blue, chestnut, brown/black, magenta, and purple.

A simple Mendelian hypothesis suggests itself immediately, does it not?  Three loci, each with two alleles, would yield eight phenotypic categories quite splendidly.  One of those loci must obviously control body color, with albinism (a) recessive under pigmented (A), if the pattern seen almost everywhere [7] throughout the remainder of the animal kingdom is followed in ampullariid snails.

The other two loci seem to control the coloration of the shell: background color (Y) and striping or color banding overtop of it (S).  A peculiarity of this system is that in most other animals, typically, a mutation at the locus assigned to albinism blocks all color production, everywhere.  Three of the eight varieties of mystery snails, however (gold, chestnut, and magenta), demonstrate colorless bodies but colored shells.

The invasive pests Pomacea canaliculata and P. maculata have well-known “golden” variants with a colorless body and plain yellow shell.  The shell and the body phenotypes seem to be inherited together, as a simple Mendelian recessive trait [8].  The “Giant Columbian Rams Horn” Marisa cornuarietis also has a “golden” variant, inherited as a simple Mendelian recessive, but in this case the plain, unstriped yellow shell is born by a snail with a pigmented body [9].

In the mystery snail Pomacea diffusa, the rainbow of phenotypes commonly observed in the aquarium suggests one locus analogous to that seen in P. canaliculata and M. cornuarietis, the dominant wildtype allele (S) encoding dark stripes or bands of pigmentation covering the shell.  The recessive (s) seems to encode no banding or striping, uncovering the yellow or “golden” background shell color.  I am reminded of the banding locus in the European land snail, Cepaea, which became such an important model organism in the early development of population genetics [10].

As for that second shell color locus, variation in background color independent of banding above it or body pigmentation below is unique to Pomacea diffusa, in my experience.  I have never seen anything like it anywhere in The Mollusca.  But two alleles again seem to be involved: let’s suggest a dominant yellow background (Y) and a recessive colorless (y).  The implication of the model is that as many as three separate biochemical pathways seem to control mystery snail coloration, yielding eight phenotypes, such that the wildtype brown/black phenotype is encoded A_Y_S_ and the completely colorless ivory variety aayyss.  If the model holds.

The three-locus model I have outlined above is not new or original with me.  It seems to have been a part of the lore of mystery snail husbandry for many years [11].  And there are most certainly some very clever and resourceful snail breeders somewhere in the world who could confirm it in a heartbeat.  But to this day, no formal test has ever been published.  The entire, lovely system – all those exciting phenotypes and the intellectually-gratifying hypotheses that go with them – remain anecdotal, untested, and undocumented in the world at large.

Because, in all fairness, those clever and resourceful snail breeders who developed all those lovely gold and purple and jade and ivory snail varieties have reaped some not-insignificant financial reward for their time and effort, would like to reap more, and consider the genetics behind their product a trade secret.  I understand that.

But doggone it, I myself am a professional mollusk geneticist, retired and bored, with nothing better to do with my life than science.  I have a testable hypothesis about the inheritance of color polymorphism in a promising freshwater gastropod model, and I want to see it tested.  And if that hypothesis could be confirmed, all those striking genetic markers could be powerful tools to answer all sorts of additional questions about the biology of the Ampullariidae, a fascinating family of God’s critters, like for example, the consequences of multiple insemination, the potential for sperm competition, and the capacity for sperm storage, see five paragraphs further down.

The experiments necessary to confirm our three-locus model for the inheritance of color polymorphism in Pomacea diffusa are not complicated.  But they require time, patience, attention to detail, and some significant experience with a very specialized little corner of animal husbandry.  The ampullariid diet is non-trivial.  The egg laying, the hatching, and the rearing of juveniles all require special techniques.  And the experiment will require space.  Mystery snails are substantial animals – their culture requires relatively large volumes of water.

Kyra's basement, May 2020

I cultured Physa and a variety of other pulmonates in my lab for many years, and a couple prosobranch species as well [12], and was repeatedly surprised, perhaps even dismayed, by the requirement of simple space – just open, flat space on shelf and lab bench.  There were times in my career that I was covering hundreds of square feet culturing snails with a maximum adult size of 30 mg.  Adult mystery snails are two orders of magnitude larger than Physa.  Am I going to go hat in hand and ask my wife for thousands of square feet in our suburban home to culture Pomacea?

So back in 2017, doing research for a six-part series on freshwater gastropods in the home aquarium [14], I started lurking about in [15] Facebook groups formed by mystery snail enthusiasts.  There were at that time 1,818 members of a Facebook group called “Mystery Snail Addiction,” 3,166 members of a group called “Mystery Snails and Aquatic Lovers,” and 5,442 members of a group called “Snails, Snails, Snails.”  And an idea dawned on me.

The idea is called “crowdsourcing.”  Paging through screenfuls of excited chatter about mystery snails, with images and videos about every conceivable aspect of their life habit and zany antics, it occurred to me that I might be able to attract a large number of talented and enthusiastic volunteers for what I decided to call “The Mystery Snail Color Genetics Project.”

So, I whipped up a modest website of eleven pages, including biological background, genetic model, and three pages of experimental design.  In broad outline, I guided potential collaborators through a trihybrid testcross, starting with an ivory line (aayyss) and a brown/black (AAYYSS), backcrossing the F1 to the ivory to test for linkage.  The biggest challenge was that, absent any data on the question, I felt as though we needed to assume that females store sperm for life, and hence virgin females would be required.  Hit the link below in a new window to see the website if you are curious.  Or a pdf of the entire website is available as FWGNA Circular Number 7 from footnote [16] below.


Notice in particular that step #1 for all new recruits to the MSCGP army was to email me.  I really wanted to establish a direct relationship with every volunteer and try to learn a bit about each of them personally.  I didn’t want to discourage anybody, but I did want to make it clear that what we are doing together is real science.  We will have standards.  No screwing around.

I announced the MSCGP to the three Facebook groups on November 8, 2018, appealing for volunteers, pointing interested parties to the website, and inviting email inquiries.  And braced myself at my laptop for the excited torrent of likes, loves, emojis, comments, questions and wisecracks I felt sure would pour forth.

And in fact, my posts on those three FB sites did reap 6 likes and 4 comments.  Zero shares, but I don’t know what a “share” is, in this context, so that doesn’t matter, does it?  How many followers do I have, I wondered?  Am I an influencer yet?

But I will admit to considerable disappointment when just one of those 6 likers and 4 commenters emailed me directly, a nice young man in Australia, who said he would love to become involved, but no ivory mystery snails were available in his country.  And my posts disappeared off the bottom of the feeds of all three of those FB sites in a matter of hours, gone without a trace.

I received a second inquiry in January of 2019, a third in August, and then two more in November of 2019, a year after I posted my appeal for volunteers.  This was not the response that I was expecting, either in quantity or in quality.

All of these inquiries came from folks who had googled up the MSCGP website and were curious to hear any results we might have obtained.  All were keeping mystery snails as pets, and had some success in reproduction, and were intrigued by color variation in the offspring.  No results so far, I always replied cheerily, but would you like to volunteer?  And one of them did.

Ms. Kyra Hall, who was one of the two who emailed me in November of 2019, was the first serious volunteer recruited into the Mystery Snail Color Genetics Project.  She ultimately pushed the effort further than any other collaborator to the present day, hatching out quite a few pure ivory sibships and attempting to rear them in isolation.  She actually got to the point that she needed true breeding wildtype females, to lay clutches of brown/black offspring with which to cross her ivories.  And it was not until this late date, well into the winter of 2019, that it occurred to me that developing a true-breeding dominant line might be more difficult than a true-breeding recessive.

Beach Blvd, Jacksonville.
We have absolutely no idea on the genetic background of the mystery snails we find for retail sale in aquarium stores.  What would make anybody assume that a snail demonstrating the dominant phenotype was true-breeding?  In fact, it might be more fun if they weren’t, so that dominant mothers might lay interestingly diverse and colorful F1 sibships.  The more I thought about it, I could see some argument for the mysterious snail breeders at the Mystery Snail Factory to purposefully outcross their brown/black stocks before retail sale, if for no other reason than to prevent competitors from developing such stocks on their own.

Might a few generations in the wild select out any weirdo genes bred into Pomacea diffusa stocks for commercial purposes?  Might a naturalized population be the best source of AAYYSS broodstock?  Hmmm.  Pomacea diffusa populations are not commonly reported in the wild [17].

I had known the late Bill Frank for many years, primarily as the steward of the quirky and entertaining jaxshells.org website.  Bill discovered a naturalized population of Pomacea diffusa inhabiting drainage ditches by Beach Boulevard in East Jacksonville in 2006, and posted the discovery on jaxshells.org, and it is probably my browsing across his black, blue, and wisteria-hued webpage [html] that brought the phenomenon to my attention.

So, I emailed my buddy Bill, and asked him if he had ever seen any color polymorphism in his Beach Blvd population of P. diffusa.  And he said no.  And so it came to pass that on December 5, 2019, I pulled into the Denny’s parking lot for my rendezvous with Bill.  The man was as colorful as the palate of his webpages.  I cannot remember the last time I met anybody, at any station young or old, so dedicated, so enthusiastic, so enthralled by trash snails in a weedy ditch.  This world needs more Bill Franks [18].

And the English thesaurus needs more choices under the noun, “ditch.”  Here at home in the Carolina Lowcountry, our drainage ditches are dug to carry away stormwater.  They are almost always dry.  But down in Florida, it is my impression that most ditches are mostly wet, and often transmit significant volumes of groundwater.  The water in the ditches that Bill showed me that morning by Beach Blvd was demonstrating some non-negligible flow, even though it had not rained recently, the water clear and coolish [19].

Bill and I were able to find a dozen adult P. diffusa in about two hours’ effort, combing through the ditches on both sides of the road.  Against the background of his long-term observations of the population dynamics, Bill considered this result a very good catch.  I carried our fresh wildstock back to Charleston that evening and sent a subset by overnight express to Kyra the next day.

The females among them were, in fact, very healthy and fecund, and Kyra was able to hatch quite a few nice clutches of 100% wildtype brown/black progeny.  But alas, her efforts to affect an ivory x brown/black cross did not come to fruition.

Kyra had to move into an apartment in late 2020, effectively bringing to a close her budding career in gastropod genetics.  “Life got in the way,” she explained.  But as annus horribilis 2020 unfolded, from worldwide coronavirus panic to nationwide political ignominy, I was somewhat surprised and really quite gratified to receive an additional nine email inquiries from potential volunteers, a broad assortment of hobbyists who had googled for information on the inheritance of color polymorphism in mystery snails and happened upon the MSCGP website.

And again, although most of those nine did not ultimately initiate experiments, as far as I know, several of them did, at least one or two of whom made serious efforts.  And in 2021 I received inquiries from another ten potential volunteers, a subset of whom initiated experiments, a subset of whom made serious efforts.  And in 2022 I received seven additional inquiries.  So that, as 2022 came to a close, I had exchanged at least some correspondence with a total of 31 potential volunteers for the mystery snail color genetics project.  I should at this point acknowledge Joanna Walthuis, Leigh Charest, John Hynes, and Rachel Voss for significant contributions of time and effort to the MSCGP at intervals during our history.

On February 16, 2023 I sent out a group email to the entire list of N=31 in my MSCGP address book, just to see what the current status of our project might be.  I received ten replies, four of which came from volunteers who still have active experiments underway.  The six respondents who have retired from the field were evenly split, three citing technical difficulties and three reporting, like Kyra, that “life got in the way.”

Kyra's Library, February 2020
The bottom line remains, however, blank.  Here about halfway through the fifth year of the Mystery Snail Color Genetics Project, we have yet to record our first datum.  The consensus from the rank and file seems to reinforce a concern I myself have harbored since I first outlined the experimental design back in 2018.  Rearing pairs of snails in cups, even large (20 oz ones) may require an impractical frequency of water change, and scaling up to one-gallon containers may require an impractical amount of space.  I am just not sure that the pretty experiment I have outlined on the chalk board can be conducted in a private residence, by a private citizen with a job other than snail farming.

Would anybody like to prove me wrong, by proving me right?  Shoot me an email at DillonR@fwgna.org.  The MSCGP is still looking for volunteers!


[1] In yet another demonstration of the folly of legislating common names, the official, AFS-sanctioned common name for Pomacea diffusa/bridgesii is “spike-topped apple snail” [2].  But I suspect that the generic term “apple snail” has become too closely associated with invasive pests for the comfort of the aquarium trade.  For whatever reason, for quite a few years now the breeders and retailers have been marking “mystery snails” on their aquaria of Pomacea diffusa.  And if that’s what it says on your sales receipt, that’s what it is when you get home.

[2] Turgeon, D.D., J.F. Quinn, A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelson, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and G.D. Williams (1998) Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks (second edition), American Fisheries Society Special Publication 26, Bethesda, Maryland, 526 pp.

[3]  I am quoting the “late 1960s” domestication date for P. diffusa from the 1996 book by Perera & Walls, page 36.  Whether all eight color varieties were available at that early date, I do not know.  All varieties were certainly on the market by 1996, as evidenced by their photos in:

  • Perera, G. and J.G. Walls (1996) Apple Snails in The Aquarium.  T.F.H. Publications, Neptune City, NJ

[4] Rawlings, T.A., K. A. Hayes, R. H. Cowie, and T. M. Collins (2007)  The identity, distribution, and impacts of non-native apple snails in the continental United States.  BMC Evolutionary Biology 7: 97

[5] Blume, W. (1957) Eine bis heute unbekannte Unterart von Pomacea bridgesii Rve.  Opuscula Zoologica 1: 1 – 2.

[6] We have directed at least ten or twelve posts on the blog to invasive apple snails of the P. canaliculata/maculata type over the last 20 years.  For an entry into their extensive literature, see:

  • REVIEW: Global Advances in Apple Snails [24May07]
  • Two dispatches from the Pomacea front [14Aug08]
  • Pomacea news [25July13]
  • Invasive species updates [13June18]

[7] Actually, we have documented two complementing albinism loci in our own favorite experimental animal, Physa acuta.  See:

  • Albinism and sex allocation in Physa [2Nov18]

[8] Yusa, Y. (2004) Inheritance of colour polymorphism and the pattern of sperm competition in the apple snail Pomacea canaliculata (Gastropoda: Ampullariidae). Journal of Molluscan Studies 70: 43 – 48.

[9] Dillon, R. T.  (1998-99)  The inheritance of golden, a shell color variant of Marisa cornuarietis. Malacological Review 31/32: 155-157. [PDF]

[10] Cain, A.J., P.M. Sheppard, and J.M.B. King (1968) The genetics of some morphs and varieties of Cepaea nemoralis (L).  Philosophical Transactions of the Royal Society B 253: 383 – 396.  For more, see

[11] In 2005 Stijn Ghesquiere added a “Genetics” page to his world-renowned applesnail.net website, without attribution, featuring a three-locus, eight phenotype Mendelian model very clearly developed and demonstrated.

[12] In addition to the Marisa I reared for my 1999 paper [9], I also had one extended experience with Pleurocera proxima [13], which was a huge pain in the ass.  I know, however, that I’m exaggerating about the “thousands of square feet” estimate up above.  But give it to me – I’m trying to avoid an argument with my wife here.

[13] Dillon, R.T. (1986) Inheritance of isozyme phenotype at three loci in the freshwater snail, Goniobasis proxima: Mother-offspring analysis and an artificial introduction. Biochemical Genetics 24: 281-290.  [PDF]

[14] Here’s my entire series on freshwater gastropods in the home aquarium:

  • What’s Out There? [9Oct17]
  • Loved To Death? [6Nov17]
  • Pet Shop Malacology [21Dec17]
  • Snails By Mail [24Jan18]
  • Freshwater Gastropods and Social Media [14Feb17]
  • Psst, Buddy!  Wanna Buy An Apple Snail? [16Mar18]

[15] Here's a funny demonstration of how unlearned I am in the ways of social media.  In my original essay of 6June23 I used the verb "ghosting" here, to describe reading FB posts without commenting or participating in any way.  On 8June23 my MSCGP colleague "Dylan" sent me an email correcting my verb choice to "lurking."

[16] Dillon, R. T., Jr. (2018) Welcome to the mystery snail color genetics project!  FWGNA Circular 7: 1 - 13.  [pdf]

[17] The USGS Nonindigineous aquatic species database lists 42 records of P. bridgesii/diffusa, as compared to 2,948 records for “Pomacea cf. canaliculata/maculata.”

[18] Here is Bill’s obituary: William Michael Frank (18Sep47 – 16Sept22)

[19] In addition to Pomacea diffusa, the "ditches" along Jacksonville's Beach Blvd are inhabited by Pomacea paludosa, Melanoides tuberculata, and Hebetancylus excentricus.