CPP Diary: What is Pleurocera (aka Melania, aka Goniobasis, aka Elimia) ebenum?

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023b)  CPP Diary: What is Pleurocera (AKA Melania, AKA Goniobasis, AKA Elimia) ebenum?  Pp 17 – 24 in The Freshwater Gastropods of North America Volume 6, Yankees at The Gap, and Other Essays.  FWGNA Project, Charleston, SC.

Looking back on my long and checkered career as a malacologist, I think I first developed my mental image of Pleurocera ebenum on a brief side trip to the Falls of the Cumberland in the summer of 1988.  There in the Kentucky State Park, above the falls only – not below – I found the rocks covered with pale, large-bodied pleurocerids bearing heavy, triangular shells that I assumed must be P. ebenum [1].  See the example at far right below.

Well, they certainly matched Figure 370 [2] in Burch [3], second from left below.  And Burch must have Goodrich’s collections at his fingertips for reference, yes?  And Goodrich [4] specifically listed “Cumberland River above the Falls” in the range of Goniobasis (aka Elimia, aka Pleurocera) ebenum, yes?

From left: Lea's original figure of M. ebenum [9], Tryon from Burch [2], Branson [6], fresh from the Falls of The Cumberland

So the FWGNA Project began our initial surveys of the Cumberland drainages about ten years ago, and in the last couple years, as we have sewed up the Green River and the Kentucky River further north, The Cumberland has increasingly come into focus.  Branson [5] promised us that P. ebenum would be “common” in Kentucky, publishing the (rather shabby) figure 27 third from left in the figure above.  And this is the description Branson provided in his key to identify it [6]: 

“Upper whorls without carinae on periphery of whorls; shell obtusely conical, smooth, spire relatively short; aperture often with purplish tinge within; Cumberland River system”

So indeed, as our survey has progressed, we have found populations of pale, large-bodied pleurocerids bearing heavy shells “obtusely conical, smooth, spire relatively short” in mid-sized rivers and streams all over the Bluegrass State, and Middle Tennessee as well.

And almost everywhere we found populations of P. ebenum, we discovered smaller, darker-bodied populations of Pleurocera simplex in small creeks upstream, bearing gracile shells with higher, more slender spires, convex even to the point of being teardrop-shaped in their outline.  Scroll down to Figure J at the bottom of last month’s post to see a typical example.  Upon careful study, we simply have not been able to draw a line between simplex populations upstream and ebenum populations downstream, anywhere.  It has become apparent that the simplex/ebenum relationship must be yet another case of cryptic phenotypic plasticity (CPP), and that ebenum (Lea 1841) is best considered a subspecies [7] of simplex (Say 1825), following the model laid down for us in the Duck River Lithasia by Goodrich [8].

It was only very recently, quite late in the entire process, that I actually read Isaac Lea’s 1843 description [9] of Melania [10] ebenum: 

“Shell smooth, obtusely conical, thick, black; spire obtuse; sutures small; whorls somewhat convex; aperture rather large, ovate, subangular at base, within purplish”

The “habitat” Lea gave surprised me, a bit: “Robinson County, Tenn. Dr. Currey.”  Tennessee has no constituent “Robinson” County, but a Robertson County was organized in 1796 about ten miles north of Nashville.  The county lies on a plateau draining west to the Red River, entering the Cumberland at Clarksville, about 65 miles downstream from Nashville.  There isn’t much mid-sized riverine habitat especially suitable for P. ebenum in Robertson County.

I was also surprised by Lea’s remarks that his M. ebenum were “very dark-coloured” with “convex” whorls and “usually purplish on the whole of the inside of the aperture.”  Those characters sound much, much more like typical Pleurocera simplex to me.

M = Springfield, N = Tyree Springs, O = Shackle Island

Did Lea have pale, triangular, heavily-shelled specimens on his desk when he described his Melania ebenum in 1841 [9]?  That would make the taxon a subspecies of P. simplex today.  Or were Lea’s specimens indeed dark, gracile, and teardrop shaped?  Is it possible that Lea’s ebenum is just a simple synonym of P. simplex today, rightly consigned to the dustbin?

So the evening of 15May19 found me checking into a cheap motel in Goodlettsville, north of Nashville, with big plans to find Isaac Lea’s type locality on the morrow.  The “Dr. Currey” referred to by Lea must have been Dr. Richard Owen Currey (1816 – 1865), the prominent Nashville physician impeccably credentialed with a Presbyterian heritage and University of Pennsylvania degree.  So, my plan was to survey the rivers and streams of southern and eastern Robertson County first, closest to Nashville, then expand my search area north and west as necessary.

The morning of 16May19 dawned crisp and clear.  And I enjoyed lovely field conditions surveying the pretty little springs and streams of southern Robertson County, taking three good swings, striking out.  So I headed west, and on my second at-bat, made solid contact in Springfield, the county seat (M, above).   I found three species of pleurocerids inhabiting Sulfur Fork at the US 431 bridge in Springfield, although none common: P. laqueata, P. troostiana, and (sure enough) P. simplex of triangular, heavily-shelled ebenum morphology [11].  Could this be Isaac Lea’s type locality?  If so, the subspecies hypothesis would seem justified.

The only misgivings I continued to harbor about the population at Springfield, however, were that the animals, in both shell and body, were pale brown, with white apertures, as (I have always assumed) typical for ebenum.  They were not the “very dark-colour” specified by Lea, nor did they sport “purplish” apertures nor “convex” whorls.  And Springfield is 30 miles north of Nashville.  Is that too far afield in 1841?

In any case, I turned my pickup back toward Nashville, with other field objectives now rising higher on my agenda.  And my route happened to take me south down TN 258, by an historic marker for Tyree Springs.  And there, at Site N, I stumbled upon a very attractive nominee for the type locality of Melania ebenum.

All I know about the history of the place you can read for yourself on the sign (click for larger).  There doesn’t seem to be any evidence of a resort at the site today – just second-growth forest and the little stream that runs under the road at far left in the photo above.  And the rocks of that little stream are covered with pleurocerids bearing thick, black shells, with obtuse spires, small sutures, whorls somewhat convex, and apertures rather large, ovate, and within purplish [12].  In other words, absolutely typical P. simplex.  If Tyree Springs is (indeed) the type locality of Lea’s ebenum, the simple-synonym hypothesis must prevail.

Tyree Springs is a comfortable day trip via horse-and-buggy from Nashville.  It is easy to imagine that a prominent physician such as Dr. Currey would be familiar with such a place in 1841.  There is just one problem.  Tyree Springs are not located in “Robinson” County nor even in Robertson County.  The springs are located in Sumner County.  The Robertson County line is another couple miles north up the ridge.

Topotype nominees: (M) Springfield, (N) Tyree Springs, (O) Shackle Island

Tyree Springs drain south, through Drakes Creek into the Cumberland River above Nashville.  So more out of intellectual curiosity than anything else, I drove downstream to sample Drakes Creek at the little town of Shackle Island [13], marked O on the map above.  And there I found a sparse population of pleurocerids bearing the paler, heavier shells with flat whorls and white apertures I have always considered typical of the ebenum form.  The Drakes Creek population of P. simplex, from headwaters to mouth, demonstrates a textbook case of cryptic phenotypic plasticity.

As I pointed my pickup back toward home on the evening of 16May19, I admit to a bit of frustration.  I wasn’t any closer to answering my questions about Pleurocera ebenum than I had been at the dawn of that long, lovely day.  In fact, the picture was murkier.

And then it occurred to me that the taxonomic situation mirrored rather beautifully the biological situation.  The taxonomic validity of Lea’s (1841) nomen ebenum is precisely as clear as the morphological distinction of those pleurocerid populations to which the name has subsequently been applied.

In the end, I resolved to follow the rule of Sunday afternoon.  The subspecies hypothesis as forwarded to us by Tryon, Goodrich/Burch, and Branson is the call on the field.  Against which there is not enough evidence to overturn.

Notes

[1] Actually, the Pleurocera population at the Falls of the Cumberland is a mixture of P. ebenum and P. semicarinata.  And the two species are difficult to distinguish here.

[2]  The great majority of the figures in Burch [3] are obviously from the pen of Mr. John Tottenham, an accomplished scientific illustrator specifically engaged for the project.  But one of the mysteries of Burch’s work is why many of his pleurocerid figures, in particular, were borrowed from elsewhere.  Burch reproduced his figure of “Elimia” ebenum from Tryon’s (1865-66) Monograph of the Family Strepomatidae.

[3] 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).

[4] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system. Occasional Papers of the Museum of Zoology, University of Michigan 417: 1 - 21.

[5] Branson, B.A. and D.L. Batch (1987)  Distribution of aquatic snails (Mollusca: Gastropoda) in Kentucky with notes on fingernail clams (Mollusca: Sphaeriidae: Corbiculidae)  Trans. Ky. Acad. Sci. 48: 62 – 70.

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

[7]  I would be most gratified if you purchased my FWGNA Volume III (Prosobranchs) [html] and read pp 77 – 91.  Or you might certainly take the easy route by clicking:

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

[8] Goodrich, C. (1934) Studies of the gastropod family Pleuroceridae - I. Occasional Papers of the Museum of Zoology, University of Michigan 286:1 - 17. For more, see:

• CPP Diary: The spurious Lithasia of Caney Fork [4Sept19] 

[9] Isaac Lea published his brief, Latinate description of Melania ebenum in 1841: “New Fresh Water and Land Shells,” Proceedings of the American Philosophical Society 2: 11 – 15.  That paper he followed with a larger paper, offering more complete English descriptions, in 1843: “Description of New Fresh Water and Land Shells” Transactions of the American Philosophical Society 8: 163 – 250.

[10] Isaac Lea originally described ebenum in the genus Melania.  He created his genus Goniobasis in 1862, formally transferring ebenum and scores of additional pleurocerid species into it.  I subsumed Goniobasis under Pleurocera in 2011.  For more, see:

• Goodbye Goniobasis, Farewell Elimia [23Mar11]

[11] Perceptive readers might note that in Springfield, a pale, robust, heavily-shelled population of the ebenum form seems to inhabit a mid-sized stream without a corresponding dark, lightly-shelled simplex population upstream.  Maybe there is, or was, and I missed it?  Or maybe the Springfield ebenum population has colonized Sulfur Fork from below?

[12]  In the interest of full disclosure, it looks to me as though at least 85% of the pleurocerid population at Tyree Springs are smallish, dark Pleurocera laqueata, and another 10% or so are smallish, dark P. troostiana.  And the apical sculpture on the shells of those two populations is not strong, in many cases.  And even I had a hard time distinguishing the Tyree simplex from the laqueata.  But I refuse to entertain the possibility that Lea’s ebenum might be a junior synonym of Say’s (1829) laqueata or anything else.  Not gonna do it.  Wouldn’t be prudent.

[13] To be only slightly more precise.  My site (O) was located in Drakes Creek at the perfectly-manicured campus of the most grotesque megachurch I have ever seen.  I counted a staff of 18 sweetly-smiling pastors and 3 directors on their website, not counting the office support, building and grounds staff, rock musicians and stagehands.

CPP Diary: The spurious Lithasia of Caney Fork

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023b)  CPP Diary: The Spurious Lithasia of Caney Fork.  Pp 9 - 15 in The Freshwater Gastropods of North America Volume 6, Yankees at The Gap, and Other Essays.  FWGNA Project, Charleston, SC.

The Duck River is our Galapagos, and Calvin Goodrich our Darwin.  Or possibly our inverse-Galapagos, and our anti-Darwin, I’m not sure.  For the brilliant evolutionary insight that Goodrich glimpsed in 1934 through the lens of this rich, fresh waterway coursing through the heart of middle Tennessee was not more species, but less.

It’s an old, old story [1], but let’s tell it again.  Prior to the dawn of the modern synthesis, North American freshwater malacology recognized at least 12 – 15 species of pleurocerids in the Duck River, probably more.  The lower reaches of the Duck (e.g., Wright Bend site E) were inhabited by heavily-shelled, “obese” populations identified as Lithasia geniculata, distinguished by their shells with prominently-shouldered whorls.  The slightly-less-obese, smooth-shouldered populations of the middle reaches (e.g., US41A, at site C) were identified as Lithasia fuliginosa.  And the headwaters of the Duck River (e.g., Old Fort site B) were inhabited by Anculosa pinguis, lightly-shelled populations without any shoulders on their whorls at all.

CPP in the Lithasia geniculata of the Duck River

In 1934, Goodrich published his “Studies of the Gastropod Family Pleuroceridae I,” in which he synonymized all these forms as subspecies under L. geniculata [2].  He just did it, at the top of the section, without making any sort of declaration, or using any form of the noun “synonym,” as though his unique insight were already an article of established malacological doctrine [3].  He then meticulously documented, town to town and bridge to bridge down the length of the Duck, the gradual transition of the three subspecies from one form to the next.

Even to me, his latter-day apostle, Goodrich’s 1934 intuition about the plasticity of shell phenotype in freshwater gastropods was startlingly profound.  His “Studies in the Gastropod Family Pleuroceridae” series inspired me to coin the term “Goodrichian taxon shift” in his honor in 2007, subsequently generalized to cryptic phenotypic plasticity (CPP) by Dillon, Jacquemin and Pyron in 2013 [4].

So, six years later, Goodrich published a paper reviewing the taxonomy and distribution of the pleurocerid fauna of the Ohio River drainage in its entirety, not just the Lithasia of the Duck River but all species in all seven genera in a vast region touching 14 states [5].  And the only other population of Lithasia geniculata pinguis of which he was aware inhabited the Caney/Collins drainage of the Cumberland River, the headwaters of which interdigitate with the Duck immediately to the east, in the vicinity of McMinnville.

But alas, even in Goodrich’s day the diverse pleurocerid fauna of the Tennessee/Cumberland was rapidly disappearing in the face of impoundment, canalization, and widespread development for navigation and hydropower across the southern interior.  The Caney/Collins system was terribly impacted by the impoundment of Center Hill Lake in the late 1940s, and the same almost happened in the Duck River in the 1970s, themes to which we shall return.  Motivated by longstanding conservation concerns, in 2003 our colleagues Russ Minton and Chuck Lydeard undertook to construct a gene tree for the North American genus Lithasia [7].

Russ and Chuck a good job rounding up samples from 11 of the species and subspecies of Lithasia listed by Goodrich/Burch, 25 populations in all, sequencing in some cases as many as 6 individuals per population.  From the Duck River Russ and Chuck sequenced one population of L geniculata geniculata (1 individual), three populations of L. geniculata fuliginosa (1, 3, and 3 individuals), and one population of L. geniculata pinguis (6 individuals).  And they also included 2 individuals of nominal Lithasia geniculata pinguis from a Caney/Collins population.  And here is their gene tree:

Minton & Lydeard [7] Figure 3, modified.

By now my readership will understand gene trees are dependent variables, not independent variables [8].  You cannot work out the evolution of a set of organisms from a gene tree.  But if you have developed an evolutionary hypothesis from good solid data of some broader sort, you may be able to understand what a gene tree is telling you.

To completely unpack the message being telegraphed to us by the enigmatic arboreal specimen figured above would require at least 6 – 8 blog posts of standard length [9].  But for the present let us focus on just the two little branches labelled “geniculata pinguis” that I have circled in red.  The two sequences obtained from the 6 individuals sampled from the Duck River, D1 and D2, cluster with all the other Lithasia.  And the two sequences obtained from the Caney/Collins system, C1 and C2, are way off with pleurocerids of other genera.  To quote Minton & Lydeard verbatim: “Further work needs to be undertaken to determine the identity and placement of the Collins River taxa.”

Thanks, Captain Obvious! If Calvin Goodrich had enjoyed access to collections from the Caney/Collins system of the same quality and detail that he enjoyed for the Duck, he might well have recognized a gradual progression in the shell phenotype of Pleurocera simplex quite analogous to that he documented for Lithasia geniculata in 1934.

Most of the headwaters of Caney Fork and its tributaries (e.g., site J) are inhabited by rather typical-looking populations of the widespread Pleurocera simplex simplex, no different from those one might find in tributaries of the Holston River around Saltville, VA, from whence the species was described by Thomas Say in 1825 [11].  We featured the P. simplex population inhabiting Pistol Creek at Maryville, TN in a series of essays published in 2016 [12], and the P. simplex population inhabiting Gap Creek, TN, last month [13].  All of these populations are darkly pigmented, and bear gracile, teardrop-shaped shells such as shown in figure J below. 

And all those populations inhabit small creeks and streams primarily of groundwater.  In East Tennessee, populations of Pleurocera simplex do not typically extend into larger rivers [14].

CPP in the P. simplex of the Caney/Collins

But in tributaries of the Cumberland, Kentucky, and Green Rivers, Pleurocera simplex populations often do extend into rivers of substantial size – as long as the currents are good and the rocky substrate they require does not entirely give way to mud.  Here their shells become heavier, chunkier, and more lightly-pigmented.  Goodrich [5] identified paler, heavier-shelled populations such as are found in the Collins River at site K as “Goniobasis ebenum (Lea 1841).”

And in the largest rivers of the Caney/Collins system (e.g., site L), populations of P. simplex are so robustly shelled that they can easily be confused for Lithasia geniculata pinguis.  I speculate it may have been a sample of P. simplex that Minton & Lydeard collected from the Collins River back in 2003, demonstrating intrapopulation morphological variance so extreme as to prompt an (erroneous) identification of Lithasia.

To be clear.  Bona fide populations of Lithasia geniculata pinguis do indeed inhabit the Caney/Collins system, as Goodrich stated.  But they are typically sparse, and often swamped by dense populations of P. simplex.  Pleurocera simplex populations do not range west into the Duck River drainage, however, and so confusions of this sort did not complicate the story Goodrich told us in 1934.

So broadening the subject out through the rest of Middle Tennessee and into Kentucky.  What is this enigmatic taxon described by Isaac Lea in 1841, "Melania" (aka Goniobasis, aka Elimia, aka Pleurocera) ebenum?  Goodrich [5] identified ebenum populations through most of the Cumberland River drainage, from “Cumberland River above the falls” through “Smith’s Shoals, Pulaski County, Kentucky” west beyond Nashville to “springs and small streams” in Dickson County, Tennessee.  Could all these populations that Goodrich called "Goniobasis ebenum" be pale, triangular, robustly-shelled P. simplex?  Stay tuned.

Notes

[1] The best entry into this literature would be to purchase FWGNA Volume 3 [html] and read pages 1 – 10 and 93 – 99.  Or you could click through it piecemeal:

• The Legacy of Calvin Goodrich [23Jan07]
• Goodrichian Taxon Shift [20Feb07]
• Elimia livescens and Lithasia obovata are Pleurocera semicarinata [11July14]

Both of those latter two essays feature scans of Goodrich’s Plate 1, showing the Duck River Lithasia.

[2] Goodrich, C. (1934) Studies of the gastropod family Pleuroceridae - I. Occasional Papers of the Museum of Zoology, University of Michigan 286:1 - 17.

[3] This is actually a bit frustrating.  Looking back on Goodrich’s body of work, there is almost never anything quotable – some “Aha moment” where the fullness of his vision is revealed.  Like Charles Darwin.

[4] 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 more, see:

• Pleurocera acuta is Pleurocera canaliculata [2June13]
• Pleurocera canaliculata and the process of scientific discovery [18June13]

[5] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system. Occasional Papers of the Museum of Zoology, University of Michigan 417: 1 - 21.

[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] Minton, R.L. & C. Lydeard (2003)  Phylogeny, taxonomy, genetics, and global heritage ranks of an imperiled, freshwater snail genus Lithasia (Pleuroceridae).  Molecular Ecology 12: 75 – 87.

[8] The best entry to this complex and long-running theme would be to read FWGNA Volume 2 [html] in its entirety.  Or for a quick lick at the problem, see my essays:

• Gene trees and species trees [15July08]
• What is a species tree? [12July11]

[9] Actually, I’ve already dedicated one blog post [10] to exegesis of the obovata1/obovata2 branch way down below the Caney Fork sequences.  And maybe in a few months we’ll come back to the geniculata/fuliginosa/duttoniana problem in the Duck River and look at that in more detail.

[10] Dillon, R. T. (2014) Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata.  Zoological Studies 53:31. [pdf] For more, see:

• Elimia livescens and Lithasia obovata are Pleurocera semicarinata [11July14]

[11] Say, Thomas (1825)  Descriptions of some new species of freshwater and land snails of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 119 – 131.

[12] I explored the complex relationship between Pleurocera simplex and P. gabbiana in East Tennessee in a series of three blog posts in 2016:

• The cryptic Pleurocera of Maryville [13Sept16]
• The fat simplex of Maryville matches type [14Oct16]
• One Goodrich missed: The skinny simplex of Maryville is Pleurocera gabbiana [14Nov16]

[13] We opened our series on CPP in Pleurocera simplex last month with:

• CPP Diary: Yankees at The Gap [4Aug19]

[14] Rocks and riffles in the mid-sized rivers in East Tennessee are often covered bank-to-bank by dense populations of Pleurocera clavaeformis and Leptoxis praerosa, neither of which ranges into drainages of the Cumberland.  I wonder if East Tennessee populations of P. simplex are restricted to smaller creeks and streams by grazing competition?

CPP Diary: Yankees at The Gap

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023b)  CPP Diary: Yankees at The Gap.  Pp 1 – 7 in The Freshwater Gastropods of North America Volume 6, Yankees at The Gap, and Other Essays.  FWGNA Project, Charleston, SC.

I like Cumberland Gap.  Daniel Boone discovered this hidden doorway through the Cumberland scarp in 1775, and decided to build a road through it, and found a new state on the other side, which he named Kentucky, in honor of his favorite recipe for fried chicken.

The Gap assumed tremendous strategic importance during the War Between the States, changing hands four times.  Confederate forces under the command of Gen. Felix Zollicoffer abandoned it to Union forces under Gen. George W. Morgan in June of 1862, who was himself forced out by Gen. Edmund Kirby Smith’s confederates three months later.  Elements of Smith’s army held the gap 12 months, surrendering it a second time in September of 1863.

Detail from Capt. Lyon's Map [1]

It was during the first northern incursion of 1862 that Captain Sidney S. Lyon of the US Topographical Engineers arrived at Cumberland Gap, uninvited.  Captain Lyon was immediately ordered by General Morgan to draft a map “showing the location of the works constructed by the enemy and those erected by the forces of the United States.”  And at some point during the discharge of those duties Capt. Lyon happened to pass along Gap Creek, a lovely little stream of cold, clear water emerging from a spring above the town of Cumberland Gap, TN, and coursing freshly through its precincts at about point A.  And there he alertly stooped to capture an entire squadron of pleurocerid snails, without firing a shot.

These rebel pleurocerids he dutifully posted back behind the lines to Dr. Isaac Lea at the Academy of Natural Sciences in Philadelphia.  And in May of 1863, a scant nine months later, Lea [2] described four new species of Goniobasis “sent to me from Gap Creek and Spring by Capt. S. S. Lyon, U.S. Army,” as follows: Goniobasis aterina, G. cumberlandensis, G. porrecta, and G. vittatella.

The municipality of Cumberland Gap, Tennessee, certainly must have been a busy and exciting place during those years.  But in 1889 the first of several railroad tunnels was blasted out of the mountains above the town, and an automobile tunnel added alongside in 1996, difficult though these engineering feats certainly are to envision, for those who have not seen them.  So the pretty little town is today located down in a deep hole about a half mile below all modern arteries of commerce, as thousands of vehicles pass through tunnels high above, and nobody stops to consider the possibility that anybody might be living way down in there.

P. "aterina" at Gap Creek

I first visited the town of Cumberland Gap in 2006, in connection with a small grant from the Virginia Department of Game and Inland Fisheries to study several potentially endangered pleurocerids in Southwest Virginia.  I found the rocks of Gap Creek covered with a strikingly high density of small, dark, eroded pleurocerids matching Lea’s figures of aterina, mixed with a smattering of small, dark, eroded pleurocerids matching Lea’s figures of porrecta and vittatella [3]. 

The allozyme data collected by John Robinson and myself [6] strongly suggested that Lea’s aterina was a (chubby, dwarfed) local population of the widespread Goniobasis (now Pleurocera) simplex, and that Lea’s nomina porrecta and vittatella were attached to a (not quite as chubby, but still dwarfed) local population of the widespread Goniobasis arachnoidea (now Pleurocera troostiana).

And in fact, had I sampled Gap Creek further downstream into Tennessee in 2006, the elaborate population genetic analysis undertaken by John Robinson and myself might well have been unnecessary.  The figure below compares typical shells collected at Cumberland Gap (site A) to a couple shells I collected in 2019 at site (B), approximately 5 km south at the state route 63 bridge.  Here Gap Creek has slowed, and warmed, and taken on a richer character more typical of the East Tennessee Ridge and Valley Province.  The populations of both P. simplex and P. troostiana under that bridge bear larger, more gracile shells of completely typical shell morphology.

The pleurocerid populations of Gap Creek display the phenomenon for which the term “cryptic phenotypic plasticity” (“CPP”) was coined in 2013.  They demonstrate intrapopulation morphological variance so extreme as to prompt a (erroneous) hypothesis of speciation. Isaac Lea (and George Tryon right behind him, and Goodrich, and Burch) all thought that the eroded, dwarfed pleurocerid populations in the cold, clear, high-velocity headwaters of Gap Creek were different species than the populations in the richer waters downstream.

CPP in P. simplex and P. troostiana of Gap Ck.

In recent years the phenomenon of cryptic phenotypic plasticity has been shown very-nearly universal in the pleurocerid populations of the Eastern United States [7].  Here in the columns of this blog I have documented CPP in Pleurocera clavaeformis, Pleurocera canaliculata, Pleurocera semicarinata, and Pleurocera laqueata [8].  In the next several essays, I will extend such studies to include two of the most widespread pleurocerids in the southeast, P. simplex and P. troostiana.  And perhaps lighten the burden with a few stories along the way?  Stay tuned.

Notes

[1] Map of Cumberland-Gap and Vicinity laid down from Surveys, made by Capt. Sidney S. Lyon, acting Topographical Engineer, under Order of Genl. G. W. Morgan, commd'g. 7th Div., Army of the Ohio. Showing the location of the works constructed by the enemy and those erected by the forces of the United States.  I myself have highlighted Gap Creek in blue.

[2] 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.

[3]  There are no pleurocerids matching Lea’s figure of cumberlandensis inhabiting Gap Creek as far upstream as Cumberland Gap today.  Tryon [4] synonymized cumberlandensis under Goniobasis adusta.  Goodrich [5] synonymized both adusta and cumberlandensis under the widespread Goniobasis (now Pleurocera) clavaeformis.  And indeed, Gap Creek downstream at site B is inhabited by a P. clavaeformis population of typical shell morphology, as well as the P. simplex and P. troostiana populations that are the subject of the present essay.

[4] Tryon, G. W., Jr. 1873. Land and Freshwater Shells of North America. Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253, 435 pp. Washington, D.C

[5] Goodrich, C. 1940. The Pleuroceridae of the Ohio River system. Occasional Papers of the Museum of Zoology, University of Michigan 417:1-21.

[6] Dillon, R. T. & J. D. Robinson (2007a)  The Goniobasis ("Elimia") of southwest Virginia, I.  Population genetic survey.  Report to the Virginia Division of Game and Inland Fisheries.  25 pp.  [pdf]

[7] Dillon, R. T. (2011) Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque 1818). Malacologia 53: 265-277. [pdf]

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]

Dillon, R. T. (2014)  Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata.  Zoological Studies 53:31. [pdf]

[8] The most convenient entrance into this rather extensive literature would be to read essays 4, 12, 13, 16, 18 and 19 in:  Dillon, R.T., Jr. (2019c) Essays on The Prosobranchs.  Freshwater Gastropods of North America, Volume 3.  FWGNA Press [html].  Or, if you’d prefer to click your way through it piecemeal:

• Goodrichian taxon shift [20Feb07]
• Mobile Basin III: Pleurocera puzzles [12Oct09]
• Pleurocera acuta is Pleurocera canaliculata [3June13]
• Elimia livescens and Lithasia obovata are Pleurocera semicarinata [11July14]
• Pleurocera alveare: Another case of CPP? [7Aug18]
• Is Gyrotoma Extinct? [5Sept18]

Finding Fontigens cryptica

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023b)  Finding Fontigens cryptica.  Pp 211 – 215 in The Freshwater Gastropods of North America Volume 6, Yankees at The Gap, and Other Essays.  FWGNA Project, Charleston, SC.

Faithful readers of this blog may remember a series of essays I posted back in 2017 about Lori Schroeder’s tiny snail, the obscure hydrobiid Fontigens cryptica [1].  The species was described in 1963 by Hubricht [2] from a spring in southern Indiana about the size of a man’s fist, and has not been seen at its type locality since, despite repeated efforts to recollect it.  The only subsequent live collections have been made by J. J. (Jerry) Lewis, extracted from subterranean stream gravels at a couple widely-scattered sites in Indiana.  Our buddy Jerry has suggested that F. cryptica may be obligately adapted to the interstitial spaces of aquifers.

Lori Schroeder's tiny snail

So back in 2008 Mrs. Lori Schroeder, a talented amateur malacologist living in central Kentucky, enlisted in a Bioblitz one-year survey of the land snail fauna of the nearby Bernheim Arboretum and Research Forest.  And in addition to her land snails, in 2013 she began to run across scattered, rare hydrobiid shells in dry forest litter sampled alongside several small Bernheim streams, which she and I were ultimately able to identify as those of Fontigens cryptica.  But despite long term, persistent, and heroic efforts on her part she had not, as of 2017, been able to discover a single living individual.  As I brought my series of essays to a close, I mentioned something about Lori’s plans for a Bou-Rouch groundwater sampler and promised to keep you all posted.

A Bou-Rouch sampler is basically a hand-powered piston pump with a short intake, modified to be driven into the ground [3].  Lori and her husband Jeff did all manner of impressive research on soil types, subterranean gravels and impervious layers in the Bernheim area, purchased the necessary hardware, assembled the machine, and by the 2018 season were hard at work pumping groundwater through lady’s trouser socks ($1.00/2pk from Dollar General).  They extended their search into neighboring, privately-held tracts, exploring new springs, old wells, and small caves.  And finished the 2018 field season in failure.  Lori did not give up hope, but she did need some sort of new idea.

Meanwhile her land snail survey continued.  And a couple months ago I got an excited email from her, reporting the discovery of another dry Fontigens shell in a previously unexplored valley recently added to the Bernheim management portfolio – the Cedar Grove Tract, about 15 km north of the Harrison and Wilson Creek areas where she had been concentrating her efforts.  And the Cedar Creek drainage boasts a spring that Lori characterized as “super nice” with “ice cold crystal clear water.” 

The super-nice spring

So, on Friday morning, 24May19, a Corps of Discovery comprised of Lori, Jeff, and Bernheim Director of Conservation Mr. Andrew Berry launched an expedition to the upper regions of the Cedar Grove Tract.  This was my benediction, verbatim: “find a decent-sized rock, or rocks, DIRECTLY at the spring head.  Right where the water comes out of the ground.  Pick up that rock and look attached UNDERNEATH it.  That’s where your Fontigens will be.”

And the next day, Lori sent me glad tidings that their expedition had been crowned with success!  The photo above shows a rock ledge running to the right of the super-nice spring, as the photographer is standing in the spring run.  Under that ledge was a decent-sized rock, and attached to the underside of that decent-sized rock was one, single Fontigens cryptica.  The snail was translucent, whitish, and blind, as originally described by Hubricht in 1963.  Next time bring forceps.

Clearly the genetics of one single little white snail found under a rock at a springhead in central Kentucky cannot be studied in isolation.  The significance of Lori Schroeder’s tiny snail can only be understood contextualized by at least a rudimentary understanding of the evolution of the North American Fontigens as a group.

Phylogenetically, the group is among the most difficult to place of all the North American hydrobioid gastropods.  They share their strange, multiply-lobed penial morphology only with the Old World genus Emmericia, which prompted Morrison [4] to assign the genus to the subfamily Emmericiinae in the old Hydrobiidae (s.l.), a judgement subsequently endorsed by Hershler [5].  Dwight Taylor [6] disagreed, proposing a new subfamily Fontigentinae to contain them, a judgement endorsed by Burch [7].  The new classification system recently proposed by Wilke and colleagues [8] split out a separate Emmericiidae while retaining Fontigens in the Hydrobiidae (s.s.) on the basis of DNA sequence data from a single individual Fontigens nickliniana sampled from Michigan in 2012.  To this day, the CO1 and 18S sequences from that single F. nickliniana remain the only Fontigens data deposited in GenBank. 

From left: Andrew Berry, Fontigens cryptica, Lori Schroeder

So, I called our colleague Hsiu-Ping Liu at the University of Denver.  And it materialized that she was very much interested in the evolution of Fontigens, and that Bob Hershler had sent her a not-insubstantial collection of samples prior to his retirement last year.  And I myself am currently holding a nice collection of cave snail samples that our good friend Wil Orndorff sent me last year from the long term VA-DCR biotic survey of Virginia caves [9].  And together Hsiu-Ping and I worked up a small proposal to the Bernheim Board for a study on the evolution of Fontigens across the eastern USA.

Meanwhile Lori and Andrew have mounted several additional field trips to the Cedar Creek Spring and failed to find any additional snails.  We’ll keep you posted on progress along both fronts.

Let me leave you this month with three teasers, and a reading assignment:

• If you were a state consultant looking for a broad strip of open land to connect Interstate 65 and Interstate 71 around greater metropolitan Louisville, where might you find it?
• If you were a planner with Louisville Gas & Electric, looking for an open corridor through which to run a natural gas pipeline, where might you run it?
• How much noise can one tiny white snail make?

Now study this press release:

• New rare snail discovered on proposed pipeline, interstate connector routes [html] [pdf]

To be continued!

Notes

[1] These three essays were published earlier this year on pp 235 - 250 of my new book, The Freshwater Gastropods of North America, Volume III: Essays on the Prosobranchs [html].  To refresh your memory:

• Lori Schroeder’s Tiny Snails [17July17]
• The Most Cryptic Freshwater Gastropod in The World [6Aug17]
• Not Finding Fontigens cryptica [6Sept17]

[2] Hubricht, L. (1963)  New species of Hydrobiidae.  Nautilus 76: 138 - 140.

[3] More about the Bou-Rouch method is available at the website of the Hypogean Crustacea Recording Scheme [html]

[4]  Morrison, J. P. E. (1949)  The Cave Snails of Eastern North America (abstract).  The American Malacological Union Bulletin 15: 13 – 15.

[5] Hershler, R., J. R. Holsinger and L. Hubricht (1990)  A revision of the North American freshwater snail genus Fontigens (Prosobranchia: Hydrobiidae).  Smithsonian Contributions to Zoology 509: 1 – 49.

[6] Taylor, D. W. (1966)  A remarkable snail fauna from Coahuila, Mexico.  Veliger 9: 152-228.

[7]  Burch originally proposed his classification for the North American freshwater gastropods in 1978 (Journal de Conchyliologie 115: 1-9). His "North American Freshwater Snails" was published as an EPA manual in 1982, as three volumes of Walkerana (1980, 1982, 1988), and as a stand-alone book in 1989.

[8] Wilke T., Haase M., Hershler R., Liu H-P., Misof B., Ponder W. (2013)  Pushing short DNA fragments to the limit: Phylogenetic relationships of “hydrobioid” gastropods (Caenogastropoda: Rissooidea).  Molecular Phylogenetics and Evolution 66: 715 – 736.  For a review, see:

• The Classification of the Hydrobioids [18Aug16]

[9] We first met Wil Orndorff in my essay about an expedition for Holsingeria unthanksensis in southwest Virginia.  See pp 217 - 222 in The Freshwater Gastropods of North America, Volume III: Essays on the Prosobranchs [html].  Or:

• Cave Snail Adventure [22Aug07]

The Freshwater Gastropods of The Ohio!

We are excited to announce the grand opening of a major new web resource, The Freshwater Gastropods of The Ohio, by Martin Kohl, Ryan Evans, Mark Pyron, Tom Watters, Kevin Cummings, Will Reeves, Jeff Bailey, Mike Whitman, and myself.  Check it out:

http://www.fwgna.org/FWGO/

Here we report the results of a comprehensive freshwater gastropod survey conducted over all waters draining into the Ohio River above the mouth of the Tennessee/Cumberland, an area of some 144,000 square miles.  Roughly 37% of the 5,250 records the team gathered were from museums, 35% from natural resource agencies, and 26% from original field collections.  We identified 70 species and subspecies of freshwater gastropods inhabiting this vast study area, providing a dichotomous key, a photo gallery, range maps and ecological notes for each.

With the addition of the Ohio fauna to the faunas of the Atlantic and Tennessee drainages previously documented, the overall coverage of the Freshwater Gastropods of North America web resource has expanded from 89 to 113 species and subspecies, inhabiting all or part of 15 states.  The main FWGNA site now features an updated “Synthesis 3.0” in which every element of this diverse and far-flung fauna is ranked and classified into quartiles by incidence, using the Gaston system we pioneered back in 2013.

The entire site has been spruced up and polished to a fine sheen.  Even the bibliography has been updated, now featuring 268 entries.  Visit us again, for the first time!

20 Years of Progress in the Museums

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Twenty Years of Progress in the Museums.  Pp 9 – 13 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

The first FWGNA project was the “digitization” of museum collections.  The year was 1999, and at the dawn of the worldwide web, only two national collections of freshwater gastropods were searchable online: those of the Academy of Natural Sciences of Philadelphia (ANSP) and the Florida State Museum (FLMNH).  So the first NSF proposal a committee of nine of us wrote – Phase I of three projected phases – was to unify the freshwater gastropod holdings of 21 North American museums into a single, online database of approximately 200,000 records.  A Phase II field survey and a Phase III monographic review were set to follow [1].

That proposal was not funded.  But progress in the national museums continued, difficult though it was for me to understand at the time.  I revisited the subject of the online availability of freshwater gastropod collections ten years later, in April of 2009 [2].  And at that point, the number of national or regional mollusk collections searchable online had grown to ten.  To quote myself directly: “I’m impressed!”

Which of those ten might be the most useful for the FWGNA Project?  Research suggests that the world is inhabited by mollusks that are not freshwater snails.  And although Class = Gastropoda is a common search criterion in almost all malacological databases, Habitat or Environment = freshwater is surprisingly rare.  So my first idea was to compare the freshwater gastropod fractions of the ten museums by searching for “Family = Physidae.”  But as of 2009, several important museum databases were not even effectively searchable by family.  So as a crude estimate of the freshwater gastropod holdings of the ten databases available online as of 2009, I executed a simple search for “Campeloma.”

My results, published on this blog 15Apr2009, showed the University of Michigan Museum of Zoology (UMMZ) in the lead at Campeloma = 2,456 records, followed by the FLMNH Campeloma = 1,414, then ANSP = 890, and Harvard’s Museum of Comparative Zoology (MCZ) = 488.

Brand new, as of 2009, was the Global Biodiversity Information Facility (GBIF), hosted at Copenhagen [2].  Many of our colleagues felt as though the GBIF was the wave of the future.  And quite a few prominent North American museums were cooperating, including the USNM, ANSP, and FLMNH.  My query of the GBIF database (executed 26May09) returned Campeloma = 3,210.

So another ten years have passed.  And as impressive as C = 3,210 most certainly is, how does that statistic compare with the online freshwater gastropod records retrievable today?  Spoiler alert!  C = 11,874.

In February of 2010 a workshop was held at the National Evolutionary Synthesis Center in Durham, NC, ultimately yielding “A Strategic Plan for Establishing a Network Integrated Biocollections Alliance” [3].  And shortly thereafter, the NSF began accepting proposals to its new “Advancing Digitization of Biological Collections Program.”  The effect has been remarkable.

Initial projects were “thematic” around the various Kingdoms and Phyla of Biology, rather reminiscent of the chromosomally-based approach pioneered by the Human Genome project.  The “Thematic Collection Network” most directly relevant to our interests here was “Invert-E-Base,” kick-started in 2014 by a consortium that included our colleagues Rudiger Bieler of the Field Museum of Natural History in Chicago (FMNH), Diarmaid O’Foighil of the UMMZ, and Elizabeth Shea of the Delaware Museum of Natural History (DMNH) [4]. Ultimately Invert-E-Base grew to involve 18 US museums, universities and other institutions, including many with substantial freshwater gastropod holdings, such as the Carnegie Museum of Natural History (CMNH), the Illinois Natural History Survey (INHS), and the North Carolina Museum of Natural Sciences (NCSM).

Meanwhile, NSF also funded the “Advancing Digitization of Biodiversity Collections Program” (iDigBio) to serve as a hub for all the data being collected by the various thematic collection networks [5]. Additional contributions rolled in from all the other museums where digitization efforts had been proceeding independently, such as ANSP, USNM, FLMNH, MCZ, and so forth. 

Today the iDigBio database includes 4.3 million gastropod records held by scores of institutions worldwide, including The Canadian Museum, the British Museum, the Australian Museum, all over Europe – everywhere.  My search of the iDigBio database for Genus = Campeloma last week returned that eye-popping 11,874 figure quoted above.  And how about Family = Physidae AND Continent = North America?  Drum roll, please.  The iDigBio database boasts 31,417 records of the North American Physidae.

Here are the top-ten museums, ranked by their North American physid holdings, as I retrieved them through iDigBio last week.  The links are to their local online search facilities, if maintained, which tend to hold more current data. 

1. UMMZ 5,492
2. NMNH 5,417
3. MCZ 3,619
4. ANSP 3,415
5. FMNH 2,726
6. FLMNH 2,083
7. INHS 1,717
8. CMNH 1,051 (No local search)
9. NCSM 824
10. DMNH 653 (No local search)

Back in 2017 The American Malacological Society sponsored a symposium entitled, “The North American Mollusk Collections – A Status Report,” which subsequently yielded several excellent papers in the American Malacological Bulletin.  Here’s a tidbit I gleaned from the contribution by Sierwald and colleagues [6]:

“Of the 6.2 million cataloged lots (of mollusks), 4.5 million (73%) have undergone some form of data digitization (which includes all forms of digitization, e.g. ledger records entered, transcribed, or imported into word processor, spread sheet, or relational database formats). About 1.1 million (25%) of digitized records have been georeferenced, which represents 18% of all cataloged lots. Only 20 collections (less than 25%) claim to be fully Darwin Core compliant, however, 34 of the 66 collections with some form of digitization are searchable online through iDigBio, Arctos, or other portals, or directly through institutional websites.”

That's great, but there’s certainly still work to be done.  Prominent among those institutions not searchable online at present is the Ohio Museum of Biodiversity (OSUM) in Columbus, which boasts very significant freshwater gastropod holdings.  Our good buddy Tom Watters is gittin’ ‘er done, even as we speak.

I should conclude with a word of warning.  One of the many criticisms leveled at our FWGNA proposal way back in 1999 was simply the question of data quality.  How would we know that all those collections of freshwater snails we were proposing to digitize really were what their museum labels said they were?  Darn good question.

The reason that I have become such an avid customer of online databases over the last 20 years is that I am preparing to visit the actual collections themselves.  I print shopping lists, fasten them to an old-fashioned clipboard, and walk around the actual, physical collections, inspecting every lot personally.  Only after I have personally verified a record is it added to the FWGNA database.  One at a time.

The more powerful a tool, the more dangerous it becomes.  You  can hurt yourself with a saw, you can kill yourself with a chainsaw.  I feel sure that 100% of my readership is acutely aware that a simple Google search is simultaneously very powerful, and very dangerous, and all of us know how to use Google safely.  Exactly the same caveats pertain to the NCBI GenBank, and to the iDigBio database.  Like my Momma used to say, “You be careful with that thing now, you hear?”

Notes

[1] For more about the history of the FWGNA Project, see:

• Twenty Years of FWGNA [11July18]

[2] My 2009 museum survey was a two-parter.  See:

• Progress in the Museums [15Apr09]
• Freshwater Gastropod Databases Go Global! [26May09]

[3] A Strategic Plan for Establishing a Network Integrated Biocollections Alliance:

NIBA Brochure [pdf]

[4] Sort-of obsolete, but nevertheless interesting:

• Welcome to Invert-E-Base [html]

[5] Integrated Digitized Biocollections:

• iDigBio [html]

[6] Sierwald, P. R. Bieler, E.K. Shea and G. Rosenberg (2018) Mobilizing Mollusks: Status Update on Mollusk Collections in the U.S.A. and Canada.  American Malacological Bulletin 36(2):177-214. https://doi.org/10.4003/006.036.020