Dr. Rob Dillon, Coordinator





Monday, February 10, 2020

What was Marstonia ozarkensis?


All I know about the late Marstonia ozarkensis is what I’ve read in the newspapers.  The diminutive hydrobiid, small-bodied even by Marstonia standards, was originally described as “Pyrgulopsis ozarkensis” by A. A. Hinkley in 1915 [1] from the North Fork of the White River in north-central Arkansas, about 20 miles from the Missouri line.  Hinkley’s single-paragraph description focused entirely on the 3 mm shell (H, below), offering no anatomical observations on the animal itself, indeed no biological notes of any sort, beyond “found in shallow water on the bedrock.”

The taxon receded into utter obscurity (as opposed to mere obscurity) for 80 years, listed by Burch [2] but not figured.  Hershler [3] essentially reprinted Hinkley’s original description in his 1994 monograph with no additional observations, stating “A limited survey of this region in 1991 – 1992 did not yield this species.”  The scanning electron micrograph image of an ANSP paratype published by Hershler (a, below) was a poor likeness [4].

Marstonia ozarkensis: Hinkley [1], Hershler [3], INHS cotype.
In 1997 Wu and colleagues [5] reported the discovery of a population of P. ozarkensis in the North Fork of the White River in southern Missouri, about 45 km upstream from Hinkley’s type locality.  In 2002 Thompson & Hershler [6] resurrected the genus Marstonia and assigned Hinkley’s ozarkensis to it.  And in 2007 Christian & Hayes [7] reported a population of Marstonia ozarkensis in Mud Creek, a tributary of the Black River about 115 km east of Hinkley’s type locality.

Marstonia ozarkensis was one of the 404 “aquatic, riparian and wetland species from the Southeastern United States” listed in the megapetition filed by the Center for Biological Diversity in 2010 [8].  In response, the US Fish & Wildlife Service declared Marstonia ozarkensis “presumed extinct” in December of 2018 [9]

The authors of the FWS “Species Status Assessment” filed in August of 2018 [10] were unable to confirm the 1997 report of Wu and colleagues, finding that “the museum records cited for this population are not present in the museum database.”  And after some hemming and hawing about high levels of endemicity in North American hydrobioids, they concluded that the Mud Creek population “may be a morphologically similar undescribed species (D. Hayes, pers. comm.).”  Thus, to quote the 18Dec18 FWS press release [9] verbatim: 
Following rigorous, science-based surveys, the Ozark pyrg, a small snail native to Arkansas and Missouri, is presumed extinct, according to the U.S. Fish and Wildlife Service. No Ozark pyrgs have been confirmed in surveys since their first discovery in 1915. As a result of today’s finding, the pyrg will not be listed under the Endangered Species Act (ESA).
That sounds like the end of the story, doesn’t it?  For the Feds, it probably is.  But for us, not so much.

In late February of last year I was pleased to receive an email from Ms. Rachel Vinsel, the Manager for the Illinois Natural History Survey mollusk collection, with attached tif images of two hydrobiid shells collected in a wetland south of Chicago.  They were clearly Marstonia, but of what species?

I can boast of no special expertise in the hydrobioids, but I can picture-match with the best of ‘em.  So I pulled my trusty copy of Hershler (1994) out of the files and started thumbing through it, looking for clues to the identity of Rachel’s unknowns.  And my eyes were drawn to the poor likeness [4] of Marstonia ozarkensis reproduced at the top of this blog post.  Hershler’s figure looked like a possible match to the images Rachel had sent me.  And heck, it isn’t all that far from Chicago to Arkansas, is it?

But if I have learned anything from many years of misadventure as a jpeg naturalist, it is that there is no substitute for the actual specimens in hand.  And I happened to have a copy of the INHS freshwater gastropod holdings on my hard drive.  And I discovered that there are several lots of bona fide Marstonia ozarkensis in the INHS collection, collected by Hinkley himself in 1914.

So the next day I replied to Rachel, suggesting that her Chicago-area unknowns might represent a rediscovery of M. ozarkensis, but simultaneously emphasizing that she dig some of the bona fide M. ozarkensis out of the INHS collection and compare.  And on 25Feb19 she sent me a tif file depicting a really interesting series of little hydrobiids, featuring both her Chicago area unknowns and the INHS cotypic M. ozarkensis.

The “INHS” image at the far right of the photomontage that opened this essay was clipped from the photo Rachel sent me 25Feb19.  Three revelations struck me almost simultaneously.  First, and least importantly, Hershler’s figure, the only illustration I had seen to that point, didn’t look anything like bona fide M. ozarkensis.  Second, our Chicago-area unknowns didn’t look anything like bona fide M. ozarkensis either [11].  But thirdly and most importantly, the bona fide M. ozarkensis in the INHS did look a whole lot like something I had seen before.

And Rachel was not done.  There were additional tif files attached to her email of 25Feb19, including one that would challenge even that tiny little bit of knowledge I thought I might have been able to glean about the late Marstonia ozarkensis.  Tune in next time for, “Is Marstonia ozarkensis extinct?”


Notes

[1] Hinkley, A.A. (1915) New Fresh-water Shells from the Ozark Mountains. Proceedings of the United States National Museum, 49:587-589.  This is actually the 1916 volume of the PUSNM, but Hinkley’s date of publication is given as “December 23, 1915” in the index.

[2] 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).

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

[4] Actually, to be fair.  It seems entirely possible to me that M. ozarkensis may have demonstrated a variety of shell form, to include the relatively robust form depicted by Hershler as well as the gracile depicted by Hinkley.  And possibly carinate forms as well, like Pyrgophorus or Potamopyrus?  Maybe even to the extreme of Marstonia scalariformis, perhaps?  But let's not get ahead of ourselves.

[5] Wu, S-K, R. D. Oesch & M. E. Gordon (1997) Missouri Aquatic Snails.  Missouri Department of Conservation, Jefferson City. 97 pp.

[6] 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.

[7] Christian A. D. & D. M. Hayes (2007) Diversity and distribution of freshwater gastropods from the Ozark region of Arkansas.  Report submitted to the Arkansas Game and Fish Commission.  34 pp.

[8] Center for Biological Diversity. 2010. Petition to list 404 aquatic, riparian and wetland species from the Southeastern United States as threatened or endangered under the Endangered Species Act.  For more, see:
  • Megapetitions of the Old West [14July09]
  • Megapetitions II: Armistice Day?  [18May11]
[9] The 12/2018 findings of the USFWS on Marstonia ozarkensis can be read here:
  • Federal Register: Endangered and threatened wildlife and plants; 12-month findings on petitions to list 13 species as endangered or threatened species [19Dec18]
  • Press Release: Ozark snail species presumed extinct following science-based surveys [18Dec18]
[10] U.S. Fish and Wildlife Service. 2018. Species status assessment report for the Ozark pyrg (Marstonia ozarkensis). 6Sept18. Atlanta, GA.  [pdf]

[11] Those two little shells of which Rachel initially sent me photos are not the subject of this essay.  I’m still not 100% sure what they were, but I think Rachel and I have settled on weirdly-fat and weirdly-dark Marstonia lustrica, and it doesn’t matter for our purposes here, anyway.

Tuesday, January 7, 2020

CPP Diary: The Many Faces of Professor Troost

Editor’s note: If you have not read last month’s post, read it.  And if you did read last month’s post, go back and read it again. The essay that follows was written under the assumption that the themes developed on 6Dec19 remain fresh in the minds of our readership.

Back in August we introduced the present “CPP Diary” series with an essay focusing on the Gap Creek populations of two freshwater gastropods widespread throughout the Tennessee/Cumberland [1].  In September and October, we explored the phenomenon of cryptic phenotypic plasticity (“CPP”) in one of those, Pleurocera simplex [2].  This month let’s back up and get a fresh start at that other species, shall we?

As I mentioned in August, the mission that sent me on my first visit to Gap Creek, way back in the summer of 2006, was a comprehensive VDGIF-funded survey of the pleurocerid fauna of SW Virginia.  John Robinson and I ultimately identified 83 populations of three species in our five-county study area, including 13 populations of what we were calling, at that time, “Goniobasis arachnoidea.”  We analyzed genetic polymorphism at 11 allozyme-encoding loci in 12 of our 83 populations, including three of the “arachnoidea,” reporting our results to the VDGIF in 2007 [3].

Almost all our Virginia populations of “arachnoidea” bore slender shells with small body whorls, usually striate, at least near the apex.  Shell (B) depicted second from left below, collected from Gap Creek at the TN 63 bridge, is typical.  But while genetically matching our other arachnoidea populations, the sample we analyzed from the headwaters of Gap Creek bore entirely smooth and strikingly stunted shells as shown at far left (A).  That population is so morphologically distinctive that it was described by Isaac Lea as not one but two unique species: Melania porrecta and M. vittatella [4].  This is an obvious example of CPP.

So to what population of snails, precisely, was the nomen “arachnoidea” originally intended to apply?  John G. Anthony [5] described his Melania arachnoidea in 1854 as “rather thin, spire slender and much elevated, very strongly striated and ribbed,” giving its type locality as “a small stream emptying into the Tennessee River near London, Tennessee.”  This must be a misspelling of Loudon, the town south of Knoxville, where the Tellico Dam [6] backs up the Little Tennessee River from its mouth to Chilhowee.  

I surveyed the precincts of Loudon in the summer of 2007 and happened to sample Steekee Creek at the bridge where it enters the corporate limits (35.7242, -84.3473) on its way to The Tennessee.  There I found, in addition to P. simplex and P. gabbiana, a population of pleurocerids bearing thin shells of slender spire and strong striation such as depicted in figure (C) below. 
(A) Gap Ck upstream, (B) Gap Ck downstream, (C) Steekee Ck, (D) Sycamore Ck

Goodrich [7] considered Lea’s (1862) Goniobasis spinella a subspecies of arachnoidea (Anthony 1854).  Lea [8] gave the type locality of spinella as “Sycamore, Claiborne County, Tennessee.  On maps of Claiborne county today one can find a wide place in the road marked “Sycamore Hall,” with a Little Sycamore Creek flowing freshly by just down the hill.  I collected specimen (D) depicted at far right above on May 14 of this year, from Little Sycamore Ck at the Estes Road bridge (36.4534, -83.5076).

But wait.  Before we plunge any further into the roaring 60’s, we really ought to paddle back about 20 years and pick up Isaac Lea’s (1841) Melania teres and M. strigosa [9].  The descriptions and figures of the two 1841 species were nearly identical to each other, as well as to arachnoidea of 1854 and spinella of 1862.  The shell of teres Lea observed was “remarkably elevated” with “spire drawn out” and “last whorl very small.”  The strigosa shell he also described as “spire drawn out,” remarking as he did that “This species is somewhat like teres herein described.”  Lea did mention “striate above” for strigosa, while not mentioning any shell ornamentation for teres.

The habitat Lea gave for Melania teres (Fig 27 way down below) was just “Tennessee Dr. Troost,” too vague to send us on a hunt today, although Goodrich [7] suggested “Small streams of Walden Ridge, Tennessee, flowing eastward.”  Figure 356 is scanned from Burch [10], presumably collected from one of those Walden Ridge teres populations illustrating Goodrich’s concept of the taxon.

For strigosa Lea did a bit better, “Tennessee Dr. Troost, Holston River Dr. Warder.”  This is probably John Aston Warder (1812 – 1883), who was born in Philadelphia and lived in Cincinnati, but traveled broadly [11].

The individual shell depicted in figure (E) down below was collected from Little Flat Creek at the Emory Road bridge in August of 2010 (36.1411, -83.7961). I am offering that particular population of pleurocerids bearing shells with spires drawn out, striate above, as topotypic for M. strigosa for four reasons.  First, apparently at least some of Lea’s sample(s) came from the Holston River drainage of Tennessee, somewhere.  And second, that entire drainage is a mess.

A=Gap up, B=Gap down, C=arachnoidea, D=spinella, E=strigosa, F=striatula, T=troostiana
In the last 10 – 12 years I have surveyed the pleurocerid fauna of the entire seven-county region drained by the Holston in East Tennessee, and have only discovered populations of pleurocerids bearing striate shells with spires-drawn-out in two streams: Mossy Creek in Jefferson County, about which you just read in my essay of 6Dec19 (Don’t tell me that you didn’t) and Little Flat Creek in Knox County.  Since Mossy Creek is already the type locality of M. troostiana, it seems an unlikely nominee for the type locality of M. strigosa.  That leaves Flat Creek as the sole remaining candidate.

The third reason I am offering Flat Creek as the type locality for M. strigosa is that it is in Knox County, and Goodrich [7] subsequently suggested the range of Goniobasis strigosa as “Small streams near Knoxville, Knox County, Tennessee.”  I’m not sure that amounts to a subsequent restriction of type locality, but I do very much value Goodrich’s opinions on matters of this sort.  And the fourth reason I am offering Flat Creek as the type locality for M. strigosa is simply that the shells of the population of pleurocerids living in that little brook match Lea’s figure.  They are not as strongly striate as the Mossy Creek sample that must have been in Isaac Lea’s collection since 1836.  They are merely “striate above.”  OK, good enough.

So what strikes me most about all these pleurocerid populations – much more than the shell striae – is the character that Lea called “spire drawn out” and that Anthony called “spire slender and much elevated.”  In more modern literature, this character is sometimes measured as shell length-to-width ratio, or the ratio of body whorl length to total shell length, although the statistical analysis of ratios is problematic.  In my own research I have preferred the regression of shell width on length [12], or the regression of apex height on body whorl height [13].  Regardless of what that variable is called, or how it is measured, the heritable component can be significant [14].

I am also stricken by the ecological similarities of all these populations.  All of these nominal species – arachnoidea, spinella, strigosa, and the Gap Creek populations that Lea described as porrecta/vittatella – reach maximum abundances in small, rich creeks.  They essentially disappear from the larger rivers of East Tennessee, not unlike Pleurocera simplex, at least in this part of the world.

Lea teres [9], Burch teres [10], Lea strigosa [9], Flat Ck (E), Coahulla Ck (F)
In exactly that same environment south of Knoxville Goodrich [7] identified populations of pleurocerids bearing striate shells with small body whorls as Goniobasis striatula (Lea 1841/43).  Lea [15] gave the habitat as just “Tennessee,” no help.  Most interestingly, however, Goodrich [16] also identified pleurocerid populations collected from Coahulla Creek in Whitfield County, Georgia, as G. striatula, shown in figure (F) at far right above.  This is one of the very few elements of the pleurocerid fauna that Goodrich admitted might be shared between Tennessee River drainages to the north and drainages of the Alabama/Coosa river system draining south toward the Gulf.

We have met the Coahulla Creek pleurocerid fauna before.  It was from Coahulla Creek in the NW corner of Georgia (34.9731, -84.9505) that I collected the sample of P. carinifera I analyzed in Dillon 2011, together with its control population of P. simplex [17].  The rivers and streams at the top of the Alabama/Coosa drainage are separated from drainages of the Tennessee by a couple kilometers at most.  And the genetic differences I found between Coahulla carinifera and simplex were not dramatically different from clavaeformis and simplex populations I sampled all the way through East Tennessee up into SW Virginia.

I did not gather any genetic data on P. striatula when I was sampling pleurocerids for my 2011 study.  But their similarities with Tennessee populations of arachnoidea, spinella, and strigosa in both ecology and shell morphology are striking, are they not?

All of the names given to all of the populations we have reviewed this month: porrecta (Lea 1863), vittatella (Lea 1863), arachnoidea (Anthony 1854), spinella (Lea 1862),  teres (Lea 1841), strigosa (Lea 1841), and striatula (Lea 1841) were proposed more recently than troostiana (Lea 1838).  And all are the same thing.  Populations of one single, highly variable species of pleurocerid snail, best identified as Pleurocera troostiana, extend down the length of the Tennessee River drainage, from SW Virginia through East Tennessee, and even hop the low hills to the upper Coosa drainage in NW Georgia.

Well, we’re not anywhere near done with the subject yet, but I sense that I’m about to lose my audience, all two of you, so let’s bookmark it here.

But our story will continue onward in future episodes, as does the river, downstream into North Alabama.  By the mid-nineteenth century, the fame of Isaac Lea seems to have spread throughout our entire, muscular young country.  And prominent citizens from Huntsville, Tuscumbia, and Florence, Alabama, were scooping up samples of the local gastropod fauna, drying them on their back porches, and packing them for Philadelphia, no different from the citizens of Knoxville and Nashville.

But storm clouds were gathering over the fertile fields of American malacology.  In our next installment... Crisis!

Notes:

[1] CPP Diary: Yankees at the Gap [4Aug19]

[2] Cryptic phenotypic plasticity in Pleurocera simplex:
  • CPP Diary: The spurious Lithasia of Caney Fork [4Sept19]
  • CPP Diary: What is Pleurocera ebenum? [3Oct19]
[3] 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]

[4] 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.

[5] Anthony, J.G. (1854) Descriptions of new fluviatile shells of the genus Melania Lam., from the western states of North America.  Annals of the Lyceum of Natural History of New York 6: 80 -132.

[6] This was the infamous “snail darter” dam, that led (perhaps more than any other public works project) to the crystallization of public antipathy for the impoundment of the free-flowing waters of the USA.  For more, see:
Wheeler, W.B. & M.J. McDonald (1986)  TVA and the Tellico Dam 1936 – 1979.  University of Tennessee Press, Knoxville.

[7] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[8] Lea, Isaac (1862) Description of a new genus (Goniobasis) of the Family Melanidae and eighty-two new species. Proc. Acad. Nat. Sci., Phila., xiv, pp. 262-272.
Lea, Isaac (1863) New Melanidae of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 217 – 356.

[9] Lea, Isaac (1841) Proceedings o the American Philosophical Society 2: 11 – 15.
Lea, Isaac (1843)  Description of New Fresh Water and Land Shells.  Transactions of the American Philosophical Society 8: 163 – 250.

[10] 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).

[11] Wilson, JG & Fiske, J (1889) Appleton’s Cyclopaedia of American Biography Volume VI. Appleton, NY.

[12] Wethington, A.R., J. Wise, and R. T. Dillon (2009) Genetic and morphological characterization of the Physidae of South Carolina (Pulmonata: Basommatophora), with description of a new species.  The Nautilus 123: 282-292.  [PDF]

[13] Dillon, R. T. & J. D. Robinson (2016) The identity of the "fat simplex" population inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 16-18. [PDF]
Dillon, R. T. (2016)  Match of Pleurocera gabbiana (Lea, 1862) to populations cryptic under P. simplex (Say, 1825).  Ellipsaria 18(3): 10 - 12.  [PDF]  For more, see:
  • The Fat simplex of Maryville matches type [14Oct16]
  • One Goodrich Missed: The skinny simplex of Maryville is Pleurocera gabbiana [14Nov16]
[14] Dillon, R. T. & S. J. Jacquemin (2015)  The heritability of shell morphometrics in the freshwater pulmonate gastropod Physa.  PLoS ONE 10(4) e0121962. [html] [PDF]  For more, see:
  • The heritability of shell morphology in Physa h^2 = O.819! [15Apr15]
[15] This name is another cold mess.  Lea originally described it as “Melania striata” in that same pair of 1841/43 publications cited at [9] above.  He then discovered that the specific nomen striata was preoccupied, amending it to striatula elsewhere in 1843 (Proceedings of the American Philosophical Society 2:237).  Goodness gracious it will be nice to be done with stuff like this.

[16] Goodrich, C. (1941) Pleuroceridae of the small streams of the Alabama River system. Occas. Pprs. Mus. Zool. Univ. Mich., 427, 1-10.

[17] 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]. For more, see:
  • Mobile Basin III: Pleurocera puzzles [12Oct09]
  • Goodbye Goniobasis, Farewell Elimia [23Mar11]

Friday, December 6, 2019

On the Trail of Professor Troost


The Dutch-American geologist Gerard Troost [1] had already led a full life when he stepped off the boat in Philadelphia in 1810.  He had earned a doctorate in medicine from the University of Leyden and done graduate work in crystallography at Paris.  He had been wounded in the Napoleonic Wars, served as chief scientist on an expedition to Java, and was captured and ransomed by privateers, twice, both French and English.  Sometimes we imagine that our lives today are interesting.

Gerard Troost (1776-1850)
In 1812 Troost was elected the first president of the Academy of Natural Sciences, a post he held for five years, tutoring Isaac Lea and Lardner Vanuxem.  Then in 1825 he sailed down The Ohio to “happiness, enlightenment and prosperity” at New Harmony, Indiana, with Thomas Say at his side.  Gerard Troost was not a malacologist, but he certainly had the names of a couple good ones in his Rolodex.

Troost was called away from New Harmony after just two years singing in the choir utopian by the offer of a professorship at the University of Nashville, from whence he was appointed the Tennessee State Geologist in 1831.  These duties sent him on lengthy explorations throughout the Volunteer State, bringing him to the verge of many rivers and streams blessed with rich faunas of freshwater mollusks.  He was often accompanied in the field by Dr. Richard Owen Currey (1816 – 1865), whom we mentioned in October [2], who assumed Troost’s duties as Professor of Geology in Nashville when Troost died in 1850.

Troost apparently began sending shells to his good friend Isaac Lea in Philadelphia very shortly after his 1831 appointment and continued for quite a few years.  Leafing through the Lea bibliography in Scudder [3] I see that at least 25 – 30 new species of unionids Lea described in the 1830s and 1840s were “sent to me by Professor Troost.”  And it was in honor of Professor Troost that Lea described Melania troostiana around 1838ish, approximately.

It will be remembered from last month’s post that through most of his career Isaac Lea was locked in a torrid race for the naming of species, and that the precise dates of his publications, calculated down to the afternoon, mattered a great deal, at least to him.  To establish what any of those dates might actually have been, however, demands scholarship of a higher caliber than the popgun your humble essayist comes packing.

Lea read his initial description of Melania troostiana in brief, Latinate form before the American Philosophical Society on November 4, 1836.  His (more complete, English) description appeared in the Transactions Volume 6 (New Series), Article 1, which (according to Scudder) was “printed and ready for publication” June 15, 1838 [4].  If you download a copy of Transactions Volume 6 from the Biodiversity Heritage Library, however, it very clearly states 1839 on the title page.  And (apparently in error) both Tryon [5] and Goodrich [6] give Lea’s date for the publication of troostiana as 1841.  Burch [7] and Graf [8] harken back to 1838.

But here is the thing that matters to us today.  Melania troostiana was early.  Regardless of its actual publication date, Lea’s description of Gerard Troost’s eponymous pleurocerid certainly preceded the torrent of gastropod nomina that spilled from his pen beginning in 1841 with his “New Fresh Water and Land Shells” series.  If you run your finger down the list of 199 canonical pleurocerid nomina forwarded to us by Goodrich/Burch, troostiana falls out #39 [9]. It was the second species of pleurocerid snail that Lea ever described, that stuck [10].

Lea gave the habitat of M. troostiana as “Mossy Creek, Jefferson County, Ten,” which is quite atypically precise, by 19th century standards.  His description led with “shell elevated” and followed with “thickly striated.”  But in his remarks, he focused primarily on the “sharp carina” demonstrated by the shell, and secondarily on the “numerous striae,” which reminded him of what we call today Pleurocera virginica. 

If you’re not entirely sure about the distinction between a carination and a striation, click the image below for a primer on shell morphology.

I speculate that the nomen “Melania troostiana” receded into obscurity in the 20th century for two reasons.  First, Lea’s 1838 figure doesn’t match any pleurocerid that currently lives or ever has lived in the state of Tennessee especially well, particularly with respect to that dramatic carination that extends from the juvenile into the adult whorls.  Hence all subsequent authors have restricted its range to Mossy Creek.

Pleurocera troostiana (Click for shell terminology)
And second, Mossy Creek is a mess.  I had the occasion to visit that unfortunate little body of water in the summer of 2011, when I was surveying the Tennessee drainage above Chattanooga for the FWGTN web resource.  The Mossy Creek catchment is a mixture of overly-grazed pastureland and dusty rock quarries, draining directly through Jefferson City into Cherokee Reservoir.  The creek has obviously suffered decades of erosion, sedimentation, and enrichment.  And at most of the (rather few) points of access I found no pleurocerids whatsoever.

My resolve was reinforced, however, by the troostiana figure in Burch [7], which looked both modern and plausible.  The UMMZ does hold three lots identified as P. troostiana collected from Mossy Creek by somebody named “Andrews.”  I don’t see any collection dates in their online database, but it seems possible to me that Andrews might have been a Goodrich contemporary, and hence his samples might be relatively recent.  And most interestingly, Burch’s figure, almost certainly from one of those UMMZ lots, does not show that weirdly strong carination.

Ultimately, I was able to find exactly N = 6 topotypic specimens of P. troostiana in Mossy Creek at the Old Andrew Johnson Highway bridge (36.1272, -83.4862) [11].  The shells borne by all six of those specimens were striate, although in one case (T1, above) the striae became obsolete in spots.  Three of the shells matched the figure in Burch quite closely.  And shells of two individuals (T2, above) were so strongly striate that a carination developed reminiscent of Lea’s original figure.

Seven paragraphs ago I wrote that “the” thing that matters to us today is that the nomen, “Melania troostiana” was early.  Let me modify that slightly.  The earliness of the taxonomic act is certainly important.  But just as important is the tremendous variability in shell striation depicted in the figure above.  All four of those shells were borne by a single population of snails inhabiting a single little ten km creek in East Tennessee.  Let that sink in a minute.

Goodrich devoted the entirety of paper number V in his “Studies of the Gastropod Family Pleuroceridae” series [12] to documenting the “transient, sporadic” character of shell “spirals,” or striations.  Selecting “Goniobasis porrecta Lea of the big hillside spring at Cumberland Gap” as one of his many examples, Goodrich observed: 
“No multistriate specimens have been seen as from the type locality, but such individuals amount to 32.4 per cent of seventy-seven shells taken from Gap Spring Creek about four miles below the spring.”
Hey kids, test your memory!  We devoted our entire essay back in August to cryptic phenotypic plasticity in the pleurocerid populations of Gap Spring Creek.  With what name did I identify those populations that Isaac Lea described in 1863 as Goniobasis porrecta?  Answer at footnote [13] below!  Next month, we’ll find out why.


Notes:

[1] The biographical details for this month’s essay, as well as the striking figure, were extracted from a “Sketch of Gerard Troost,” published anonymously in the June, 1894 issue of The Popular Science Monthly, pp 258 – 264.

[2] It was Currey who sent Isaac Lea the sample of pleurocerids from “Robinson County, Tenn” he described as Melania ebenum in 1843.  See:
  • CPP Diary: What is Pleurocera (aka Melania, aka Goniobasis, aka Elimia) ebenum?  [3Oct19]
[3] Scudder, N. P. (1885)  Bibliographies of American naturalists – II. The published writings of Isaac Lea, LL.D.  Bull. US National Museum 23: 1 – 278.

[4] Lea, Isaac (1838-39) Description of New Freshwater and Land Shells.  Transactions of the American Philosophical Society (New Series) 6: 1 – 154.

[5] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

[6] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[7] 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).

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

[9] The first valid species of pleurocerid snail described by Isaac Lea, by the Goodrich/Burch canon, was Melania acuta (Lea 1831).  This is not the Pleurocera acuta of Say (1821).  This is a “longitudinally undulated and transversely lineated” North Alabama species attributed to Goniobasis by Goodrich, or Elimia by Burch.  Maybe a synonym of laqueata (Say 1829)?  Not sure.

[10] Nineteen of the 38 canonical pleurocerid taxa older than 1838 were described by Lea’s nemesis, Timothy Abbott Conrad, which must have ticked him off royally.  Another 12 were from Thomas Say, whom Lea didn’t much care for either, apparently.  See last month's post:
  • Isaac Lea drives me nuts [5Nov19]
[11] I’ll post a dot-map showing the site of my Mossy Creek collection next month.

[12] Goodrich, C. (1935)  Studies of the gastropod family Pleuroceridae – V.  Occasional Papers of the Museum of Zoology, University of Michigan 318: 1 – 12.

[13] I identified the Gap Creek population of G. porrecta as Pleurocera troostiana, of course!  That’s where I’ve been going with this entire essay.  Shame on you for reading this footnote.  Go back and read:
  • CPP Diary: Yankees at The Gap [4Aug19]

Tuesday, November 5, 2019

Isaac Lea Drives Me Nuts


He was born the fifth son of an affluent Quaker merchant in the bustling port of Wilmington, DE, and sent to Philadelphia at age 15 to work in the importing and wholesaling business with his eldest brother.  In Philadelphia he struck up a friendship with Lardner Vanuxem (1792 - 1848) also the son of a prominent Quaker merchant, and the pair became interested in natural history together, focusing especially, at this early date, on rocks, minerals, and fossils.  In 1814 both Lea and Vanuxem joined a volunteer rifle company, and were expelled from the Religious Society of Friends wholesale, which was the way their community preferred to do business, in those days.

Isaac Lea (1792 - 1886) [1]
In 1815 Lea and Vanuxem were elected to membership in the Academy of Natural Sciences of Philadelphia, then in existence for three years.  Prominent among the founders of the Academy was, of course, Thomas Say (1787 - 1834), the Father of American Malacology.  The biographical similarities between Say and Lea are striking: both the sons of prominent Philadelphia-area businessmen, both kicked out of the Quakers for volunteering during the War of 1812, both autodidacts.

For this essay I am relying primarily on the scholarly 1885 biography and bibliography compiled by N. P. Scudder [1], with occasional reference to W. H. Dall [2].  And one of the more peculiar aspects of both references is the absence of any exploration of the relationship between Isaac Lea and Thomas Say. On page VIII Scudder recorded: “Mr. Lea remembers that Mr. Say founded his genus Alasmodonta on a single valve which he himself had picked up on the river shore at Chilicothe, Ohio, and which he carried from that place to Philadelphia in his saddle bags.”  And that is (almost) all we know about the relationship between these two giants of American malacology today.

Vanuxem went on to the Paris School of Mines, and from thence to a university professorship.  Lea published his first paper in the Journal of the ANSP in 1817, “An account of the minerals at present known to exist in the vicinity of Philadelphia.”  But he did not pursue an academic degree of any sort [3], marrying the daughter of a prominent publisher and shifting his business to that of his father-in-law.

Scudder attributes the origin of Lea’s malacological interests to the arrival in Philadelphia of two shipments of unionid shells - one from a brother in Cincinnati, the second from the 1825 expedition of Major Long.  And in 1827 Lea published his first malacological paper, “Description of six new species of the genus Unio.”

One cannot help but notice that two years previous, Thomas Say had quit Philadelphia and sailed down The Ohio to help found the utopian community at New Harmony.  Was the malacological awakening of Isaac Lea a coincidence?  Or was there room for just one malacologist in Philadelphia?  Thomas Say had served as the chief zoologist on Major Long’s expedition to the headwaters of the Mississippi, which means, ironically, that Say may have collected the unionid shells that Lea first described, just as Lea claims to have collected unionid shells first described by Say.  The relationships among the 19th-century American malacologists seem to have been a complex thing.

For whatever reason, the explosion of malacology that erupted from the pen of Isaac Lea would continue almost unbated for 50 years.  Ultimately, he published 279 articles, papers, monographs and books, describing as he did 1,842 species.  To wit:

Species described by Isaac Lea [1]. Click for larger.
Through the 1830s, Lea focused his efforts almost exclusively on this first love, the Unionid mussels.  His first big swing at our favorite organisms came in 1841, with the publication of his “New Fresh Water and Land Shells,” in which he described 57 species of Melania, including such notables as M. clavaeformis and M. ebenum [4].  This series (using variants of the same title) continued until 1848.  In the 1850s he seems to have been distracted once again by other taxa, but he came roaring back to the freshwater gastropods in the 1860s, describing scores of additional species and four new pleurocerid genera, including Goniobasis.

I have modified the adjective “unabated” with the adverb “almost” in the sentence two paragraphs above for two reasons: Lea’s extensive European tours of 1832 and 1853.  On his return from the 1832 trip: 
“to his great astonishment he found that advantage had been taken of his absence, which had prevented him from securing his share of the collection of Tertiary fossils of Alabama, made by Dr. Gates … and that the whole of the Philadelphia quota had been placed in the hands of Mr. Conrad, who was not one of the subscribers. Mr. Lea was not made acquainted with the fact until he saw the first numbers of Mr. Conrad's published descriptions.”
This, I infer, was the beginning of a lifelong feud between Lea and Timothy Abbott Conrad (1803 – 1877), the prominent Trenton-area paleontologist and malacologist, also an excommunicated Quaker [5], elected to membership of the ANSP in 1831.  The feud also seems to have involved Thomas Say.  Because when Lea returned from his second European tour in 1853 [6], again quoting Scudder: 
“He found that Mr. Conrad had published “A Synopsis of the family of Naiades of North America” in the early part of the year, which was full of errors both of date and facts.  These were all stated in Dr. Lea's "Rectification," published immediately on his return, in order to correct any false impressions they might have given. He likewise found that Mr. Say had also published a short list of the species, in which he differed much from Mr. Conrad, but he did not give Dr. Lea a single species.” 
By his death at the age of 94 Isaac Lea had become “the Nestor of American Naturalists [7].”  He was president of the ANSP from 1858 – 1863, and (indeed!) elected president of the AAAS in 1860, and apparently lionized in his day.  He cannot be judged otherwise in ours [8].  Had the noun “species” been defined by the community of systematic biologists active in the 19th century, which I don’t think it was, it would have been something like, “a type considered distinct by a competent taxonomist,” which Isaac Lea most certainly was.  I cannot find any evidence that he ever heard of Charles Darwin [9], much less integrated evolutionary thinking into his work, but I honestly don’t think the discipline of malacology met Darwin until well into the 20th century, and it would be unfair to expect otherwise.

Would it be fair to judge Lea through the eyes of a contemporary?  George W. Tryon Jr. (1838 - 1888) was prominent in the generation of malacologists who followed in Lea’s footsteps.  In 1866 Tryon founded the “Conchological Section” of the ANSP, which he directed until his untimely death [11].  And in 1873 Tryon published the first comprehensive monograph of the North American Pleuroceridae (“Strepomatidae”) [12], in the preface of which he thanked his “kind friend [13]” Dr. Isaac Lea “who not only gave me constant access to his noble collection, but on many occasions aided me by comparing specimens and elucidating knotty questions in synonymy.”

G.W. Tryon (1838 - 1888) [11]
So as of 1873, Tryon recognized 464 valid species of pleurocerids [15] in ten genera.  His monograph is a marvelous work of scholarship, to which I refer often, but I just do not have the patience this morning to go through all 435 pages and count all the synonyms under all those 464 species.  Let me select the typical genus Pleurocera, in which Tryon recognized 99 valid species [16].
 
Thumbing through the 89 monograph pages in which Tryon reviewed the 99 species [17] of Pleurocera that he considered valid as of 1873, I count 49 real synonyms, setting aside alternate spellings.  Those synonyms comprise 29 of Isaac Lea and 20 from eight other pleurocerid researchers combined [18].  So even Tryon, who was hosted by Lea in his collection and instructed by him personally in the finer points of synonymy, considered that his kind friend, seated in bearded eminence at the high table over his right shoulder [19], had screwed up 29 times in the genus Pleurocera alone.

And the problem is even worse than it looks.  Of the 99 Pleurocera species considered valid by George Tryon, 71 were described by Isaac Lea.  If Lea had 29 more rings than he had pegs to throw them on, one would expect that he would toss them on his own pegs 71/99 = 72% of the time, and on anybody else’s pegs the remaining 28% of the time.  But in fact, only 14/29 = 48% of Lea’s synonyms were self-synonyms according to Tryon, while 15 of Lea’s synonyms were cast on the (just 28) species previously described by somebody else.

Did Isaac Lea willfully ignore the work of his colleagues?  Or was he just too busy talking to listen to anybody else?  Either way, this drives me nuts.

Well, although Calvin Goodrich (1874 - 1954) did not monograph the Pleuroceridae in any formal sense [20], through the 1930s and 1940s he effectively pared the American list of pleurocerid species and subspecies down to 199, of which a mere 93 were Isaac Lea’s.  Those 199 were sanctified by Burch [21] into holy scripture.  How many of the 93/199 = 47% of all the canonical species of North American pleurocerids described by Isaac Lea might be valid, by modern biological criteria?  We’ve nibbled around that question on several occasions in recent years [22].  We’ll take another nip at it in the next couple essays.

Notes:

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

[2] Dall, W. H. (1888)  Some American Conchologists.  Proc. Biol. Soc. Washington 4: 95 – 134.

[3] One usually sees him referred to as “Dr.” Isaac Lea.  Harvard College bestowed an honorary LL.D. on Lea in 1852.

[4] Lea. I. (1841)  New fresh water and land shells.  Proc. Amer. Philos. Soc. 2: 11 – 15.

[5] Conrad was stricken from the roll of The Religious Society of Friends in the same year he was elected to the ANSP, “because of a preference for walking afield to attending religious services.”  The Quakers founded the middle colonies and dominated them, in every way imaginable, for over a hundred years.  But today, even in the Philadelphia metro area, only approximately 1% of adults identify with the Religious Society of Friends, according to the recent Pew survey.  That’s approximately the same proportion as the Hindus.

[6]  I think the biographer Scudder may be confused here.  Conrad’s “Monography of the Family Unionidae” was published between 1835 and 1847.  And Say died in 1834.  So I think all this unionid sturm und drang kicked off after Lea’s first (1832) European tour, rather than after his second tour of 1853. Ironically, Scudder seems to be fussing about Lea fussing about Conrad screwing up dates, as Scudder is screwing up dates.  But at this point, to quote Bill Murray, “It just doesn’t matter.”

[7] This sobriquet comes from Dall [2].  And I confess that I had to google it, too.  In both The Iliad and The Odyssey, Nestor was the wise and ancient king to whom younger warriors, such as Agamemnon and Achilles, turned for advice.  The effect of Nestor’s wisdom was diluted, however, by his boastfulness.  His advice was always prefaced by lengthy accounts of his own heroic actions under similar circumstances in the distant past.

[8] One of the most unpleasant aspects of human nature is that we all set ourselves at the high bench to judge our fellow man.  And historic figures we judge by our own entirely personal, inevitably modern criteria.  So for example, in recent years we seem to have cast Thomas Jefferson into the outer darkness, convicted of the high crime of slavery, his merits as a patriot forgotten.  In the days of my youth, Jefferson was a demigod.  But turning back two pages, if you’d asked contemporaries like George Washington or John Adams, they couldn’t stand the jerk.

[9] Scudder chronicles Lea’s European tours of 1832 and 1853 in breathless detail [10], including everybody Lea met, and didn’t meet, and what everybody said to him, and what he said back.  In England he did meet Faraday, Dalton, and Lyell, among many others, but not Darwin.  William Hooker yes, his son Joseph Dalton Hooker no.  Sedgwick yes, Huxley no.

[10] Here’s an example: “Calling at the Museum of Economic Geology, Dr. Lea found Sir Henry De la Beche busily engaged. He expressed much pleasure at seeing him again. While conversing with him a very old gentleman came in whom he introduced as Mr. Weaver. He was entirely deaf, and Dr. Lea had to write his part of the dialogue.  He was ninety-one years old, was perfectly erect, and had a remarkably fine face. Dr. Lea was very much pleased to see him, for he was of the old school of science, and was a fellow-student with Humboldt. He was kind enough to say that he had heard in the hall that Dr. Lea was in the private room with Sir Henry, and he could not refrain from coming to shake hands with one who had done so much for American science.”  Don’t you wish that Scudder had chronicled anything like that detail for the relationship between Isaac Lea and Thomas Say?

[11] Ruschenberger, W.S.W. (1888) A biographical notice of George W. Tryon, Jr. Proceedings of the Academy of Natural Sciences of Philadelphia 40: 399 – 418.

[12] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

[13] Tryon was of Lutheran heritage, converted [14] to the Quakers in 1853, and then to the Unitarians in 1876, according to Ruschenberger [11].  So, the noun “friend” may have carried special meaning between Tryon and Lea in 1873.

[14] Tryon would have been 23 years old when war broke out between the states.  So, his transitory affiliation with the Quaker faith is not difficult to understand.

[15]  The number 464 was given by Tryon in his introduction.  The actual number of pleurocerid species Tryon ultimately recognized in his monograph seems to have been more, but I don’t have patience to hand-count.

[16] Tryon quoted 84 species of Pleurocera in his introduction, but by actual count there are 99.

[17] The 99 species included Pleurocera leaii Tryon, 1861.

[18] Anthony = 9, Menke = 3, Say = 2, Reeve = 2, one each for Brot, Hald, Adams, and Wood/Ward.

[19]  Yes, Isaac Lea, 46 years Tryon’s senior, predeceased him by just two years.  Dall [2] termed the first period of American malacology the “Sayian” and the second period the “Gouldian,” with only Isaac Lea surviving to link the two.

[20]  To learn more about Calvin Goodrich, I would be most gratified if you would purchase FWGNA Volume 3 [html] and read the first ten pages.  Or you could take the easy way out:
  • The Legacy of Calvin Goodrich [23Jan07]
[21] 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).

[22]  Lea hit clavaeformis but whiffed on acutocarinata and ebenum in 1841:
  • Goodrichian taxon shift [20Feb07]
  • CPP Diary: What is Pleurocera ebenum? [3Oct19]
He got a solid hit in 1862:
  • One Goodrich Missed: the skinny simplex of Maryville is Pleurocera gabbiana [14Nov16]
But went 0-for-4 in 1863:
  • CPP Diary: Yankees at The Gap [4Aug19]

Thursday, October 3, 2019

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


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 “Elimiaebenum 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.