Dr. Rob Dillon, Coordinator





Sunday, May 10, 2020

A House Divided

Editor’s Note – This the eighth essay in a seemingly-endless series on phenotypic variety and taxonomic confusion in the pleurocerids of the Tennessee/Cumberland.  To appreciate the arguments advanced below, you really must have read last month’s post, and it would help to have read December and January as well.

By the spring of 1862, America had reached a point of crisis.  Isaac Lea had run out of names for pleurocerid snails.

Between 1834 and 1861 Lea had described 184 species in the genus Melania, which he now wrote had become “so enormously extended as almost to prevent the possibility of finding suitable names for its species.”  So in April of 1862 Lea [1] proposed to split a large subset of Melania bearing shells with “auger-shaped” apertures into a new genus Trypanostoma.  And in May [2] he proposed to split another large subset bearing shells with “subrhomboidal” apertures into a second new genus, Goniobasis.

Lea then went on to describe 242 new pleurocerid species in 18 months, as though the pressure in some vast balloon of Latinate adjectives had suddenly been exploded by nomenclatorial pin prick.  The splatter included spinella which we reviewed in January [3] and the aterina / porrecta / vittatella / cumberlandensis clot we featured way back in August [3], sent to Lea by Captain Lyon from way down yonder in Cumberland Gap.  Also detonated onto the pages of learned journals in 1862/63 were a tremendous variety of additional nomina assigned to pleurocerid populations from throughout the Tennessee/Cumberland region, including Goniobasis gabbiana, which immediately arced into oblivion, only to be called back on this blog in 2016 [4].


Lea’s genus Trypanostoma never caught on.  George Tryon [5] considered it “unquestionably” a junior synonym of Rafinesque’s Pleurocera [6], as did Goodrich [7] and Burch [8].  But Lea’s genus Goniobasis was accepted by both Tryon and Goodrich as describing a “natural” group, hanging on until the 1980s, when Burch resurrected the zombie taxon, Elimia, to replace it.

We now understand, of course, that the distinction made by Lea in 1862 was illusory.  There is no  evolutionary difference between Trypanostoma, Pleurocera, Goniobasis or Elimia whatsoever [9].  The tragic rift that tore the pleurocerid fauna apart in 1862, setting brother against brother, would not be healed for 150 years.

Nevertheless, in 1873 George Tryon, almost certainly in direct consultation with Isaac Lea himself, divided all 184 species that Lea had described prior to the Trypanostoma/Goniobasis crisis of 1862 into either Pleurocera or Goniobasis.  In general, the larger and more heavily-shelled nomina went into the former genus and the more lightly-shelled species into the latter.  During that process, all five of the previously-described slender, striate East Tennessee species we discussed in January [3] were allocated to Goniobasis: troostiana (Lea, 1838), teres (Lea, 1841), strigosa (Lea, 1841), striatula (Lea 1841) and arachnoidea (Anthony 1854).  As well as the perstriata Lea described from North Alabama in 1852. 

So last month we reviewed the situation with Melania (now Goniobasis) perstriata, suggesting that the Huntsville-area populations described by Lea using that particular sobriquet might best be understood as a plicate subspecies of the troostiana population he described from East Tennessee way back in 1838.  We also hinted that quite a few additional names for similar populations inhabiting similar waters of North Alabama might have been described in the aftermath of  the 1862 unpleasantness [10].  Among these were pybasii (1862), paupercula (1862), crispa (1862) and decampii (1863).

Pleurocera troostiana populations, Note [21] and map below.

Lea led his 1863 description of Goniobasis pybasii [11] with “shell folded, very much drawn out,” and went to unusual lengths comparing it to four other species previously described: “reminds one of laqueata (Say),” “allied to deshaysiana but more slender [12],” “very much like grata (Anthony) [13],” and “differs from lyonii by not being striate [14].”  He did not distinguish pybasii from perstriata, nor indeed from any of his East Tennessee species, troostiana or any of the synonyms we reviewed in January.  Lea gave the habitat of Goniobasis pybasii as “Tuscumbia, Alabama, B. Pybas [15].”

Tryon [5] passed pybasii along verbatim.  Goodrich opened his 1930 treatment of G. pybasii [16] with the observation that “this species does not seem to have been collected in recent years.”  He did, however, examine nine shells (bearing poor data) then held by the Alabama museum, writing “The chief characteristic of the species is that, unlike the other plicate Goniobases of the region, it lacks the granulate spire and the usual revolving raised lines.”  He went on to broaden its range to “springs and streams of North Alabama.”  Burch [8] passed Elimia pybasii along on his page 140, unfigured.

So on March 12, after my tour of lovely Madison County, Alabama, I struck out across the rolling hills and lush farmlands toward Tuscumbia, the home of Hellen Keller, Annie Sullivan, and the first railroad on the American frontier [17].  And over the course of several days following, I was able to inventory, lightly but completely, the freshwater gastropod fauna inhabiting the springs and small streams of North Alabama.

And it materializes that pleurocerid populations bearing “shells folded, very much drawn out” that match Lea’s figure of 1863 are today widespread in the springs and small streams south of Tuscumbia.  And as a type locality for Goniobasis pybasii, I hasten to nominate what may be my favorite freshwater gastropod sampling site ever, the small spring and spring run at the foot of the Rattlesnake Saloon (Q).

My favorite sampling site, ever.
By great good fortune, the hour was getting on toward quitting time on a Wednesday evening when I pulled my pickup into the ample parking lot of the Rattlesnake Saloon, about 2 miles south of Tuscumbia.  The public establishment is located a brief stroll through verdant pastureland and a steep descent under a massive rock overhang about 20 – 30 yards above Newsom Springs.  Beer and pleurocerids on a warm Alabama evening in mid-March?  I cannot remember ever enjoying anything I have called “work” more than this.  See the example shell marked (Q) above.

Lea described Goniobasis paupercula [11] in the same 1863 article as pybasii, 11 pages later, giving the habitat simply as “North Alabama, Prof. Tuomey [18].”  His description of the “subcylindrical” shell mentions whorls “folded above and striate at the apex.” But in his remarks, he confessed that he had “not a single one with an entirely perfect apex, being usually decollate at the second whorl from the base.”  In contrast to pybasii, Lea did not compare paupercula to any other pleurocerid previously described – not to perstriata or anything else – implying, I suppose, that something in his description made paupercula self-evidently unique.  Possibly the decollation?  In any case, Tryon passed paupercula along uncritically.

Goodrich (1930) reported observations on seven populations of paupercula collected by H. H. Smith from small streams in Lauderdale and Franklin Counties, Alabama.  Goodrich’s notes on shell morphology expanded those of Lea considerably, especially with respect to variation in shell sculpture.  Burch [8] picked up the species from Goodrich (1940) and passed it along (with Tryon’s redraft of Lea’s original figure) on his page 140, giving the range simply as “creeks of Northern Alabama.”
Juvenile, 9.2 mm

My surveys through Lauderdale and Franklin Counties this March did not yield any pleurocerid populations bearing decollate shells.  But I did stumble upon a population bearing shells very nearly identical to Lea’s 1863 description and figure in Lipscomb Spring, south of Huntsville, on the opposite side of the Tennessee River (R).  The figure above shows an adult shell, the figure at left a juvenile, suggesting that Lea’s speculation about striae around the apex was correct.

Lea published a brief, Latinate description of Goniobasis decampii in 1863, which he followed with a more complete English description in 1866 [19].  The shell, he reported, was “plicate, striate below, greatly attenuated, thin.”  Lea gave the habitat as “Huntsville, Alabama; Wm. H. DeCamp, MD, surgeon United States Army [20].”

To quote Goodrich (1930) verbatim: 
“This mollusk is G. perstriata in all essentials save its nearly cylindrical shape.  Quite slender specimens of perstriata have been taken in Big Spring Creek at Huntsville… It is possible that the original collector, Dr. DeCamp, had visited some spring or creek in the vicinity of Huntsville containing these shells, and that the locality has not since been examined.  A ‘pure culture’ of decampii would warrant, of  course, its definite recognition.”
In my week of sampling springs and streams around North Alabama I did not find a single individual pleurocerid bearing a shell as “greatly attenuated, thin” as Lea’s figure suggests, much less a “pure  culture.”  Goodrich’s speculation seems quite plausible to me – that the single shell sent Lea by Dr. DeCamp was subsampled from the perstriata population of Big Spring, Huntsville, subsequently much impacted by development.

The biological and morphological considerations reviewed above combine to suggest to me that all three of these nominal species, pybasii (Lea 1862), paupercula (Lea 1862), and decampii (Lea 1863), are junior synonyms of Pleurocera troostiana perstriata (Lea 1852).  All three of these nineteenth-century taxa were defined entirely by their shell morphology.  And the shell morphology demonstrated by the example populations we have identified this month rests easily within the variance of the Huntsville-area P. troostiana perstriata populations we documented last month.

North Alabama.  See footnote [21] for locality data.
But regarding crispa (Lea 1862).  Lea described Goniobasis crispa from “Florence, Alabama; Rev. G. White” in the same 1863 paper as pybasii and paupercula, two pages after the latter [11].  Goodrich neglected it in his 1930 work but brought crispa back as a subspecies of Goniobasis perstriata in 1940 [7].  No, Goniobasis crispa is not a subspecies of perstriata, nor is it a synonym of troostiana, nor is it related to any other species we have treated this month, or at any time in recent memory.  Goniobasis crispa (Lea 1862) is entirely different.  And to quote my favorite Alabaman, “That’s all I’ve got to say about that.”

But I will say two more things about two other gastropod populations and close with one rhetorical question.  The first thing I will say is that the tributaries of the Elk River in North Alabama are inhabited by pleurocerids bearing slender, lightly-costate shells no different from any of the other Pleurocera troostiana perstriata populations we have reviewed in the last couple months.  See the example shell from Mechanic Branch at Sim Corder Mill (S) figured way up above.

And the second thing is that if one samples up the main Elk River just a short way into Tennessee, one begins to discover populations of pleurocerids bearing slender, high-spired shells elaborately ornamented with both strong striae and dramatic costae down the entire length of their shells, from apex to lip. See the example from the Elk River at Kelso (G) above.

What is the situation with Pleurocera troostiana in Middle Tennessee?  Stay tuned.

Notes:

[1] Lea, Isaac. (1862) Description of a New Genus (Trypanostoma), of the Family Melanidae, and of forty-five New Species. Proc. Acad. Sci., Phila., xiv, pp. 161 - 175.

[2] 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.

[3] Here’s my entire series on Pleurocera troostiana:
  • CPP Diary: Yankees at The Gap [4Aug19]
  • On the trail of Professor Troost [6Dec19]
  • The many faces of Professor Troost [7Jan20]
  • Huntsville Hunt [15Apr20]
[4] The most convenient medium by which to review the rediscovery of Pleurocera gabbiana would be to read essays 9 - 11 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:
  • 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]
[5] Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

[6] Tryon turned out to be quite wrong here.  The question of whether Lea’s Trypanostoma might indeed be a junior synonym of Rafinesque’s Pleurocera was swept up into one of the longest-running feuds in American Malacology.  See:
  • Joe Morrison and the Great Pleurocera Controversy [10Nov10]
[7] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[8] 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).

[9] Dillon, R. T., Jr. (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:
  • Goodbye Goniobasis, Farewell Elimia [23Mar11]
[10] Isaac Lea described several more heavily-shelled species of pleurocerid snails from North Alabama bearing elevated spires and sometimes even striations that were ultimately allocated to Trypanostoma/Pleurocera.  Among these were brumbyi (1852), striatum (1862) and currieranum (1863).  Goodrich [5] synonymized striatum (from “Florence, Alabama B. Pybas”) under canaliculata.  And it is my hypothesis that the “spring in Madison County” from which Goodrich identified the brumbyi/currierianum pair is Brahan Spring in Huntsville (34.7062, -86.6003), in which case, that pair of specific nomina appear to be junior synonyms of Pleurocera canaliculata as well, subspecies pyrenellum.


[11] Lea described paupercula, pybasii and crispa in brief, Latinate form in his 1862 PANSP paper cited at note [2].  They were figured and described more completely in English the next year, in:
Lea, Isaac (1863) New Melanidae of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 217 – 356.

[12] Lea’s deshaysiana of 1841/42 (habitat “Tennessee”) was synonymized under laqueata (Say1829) by Goodrich [7, 16].

[13] Anthony’s 1860 grata (habitat: “Alabama”) has been buried by the sands of time.  Rest in peace.

[14] Put a bookmark here.  We will return to the Goniobasis lyonii populations of Kentucky in a couple months.

[15] About the life of Mr. Pybas I have found nothing.  Otherwise, Tuscumbia’s Oakwood Cemetery is the final resting place of one Mr. Benjamin Pybas, d1883 aged 76 years.

[16] Goodrich, C. (1930)  Goniobases of the vicinity of Muscle Shoals.  Occasional Papers of the Museum of Zoology, University of Michigan 209: 1 – 25.

[17] In 1834 local merchants completed a railroad from Decatur to Tuscumbia to bypass the 43-mile Muscle Shoals of the Tennessee River.  This line was incorporated into the Memphis & Charleston Railroad in 1850, ultimately becoming the first connection between Alabama and The East.  Cotton was, of course, the primary motivation for the construction of these commercial arteries.  The conduct of freshwater gastropods to Philadelphia was apparently an afterthought.

[18] Michael Tuomey (1805 – 1857), professor of geology at the University of Alabama, appointed first state geologist of Alabama in 1848, working out of Tuscaloosa, travelling broadly.

[19] Brief, Latinate description of Goniobasis decampii:
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.
English description with figure:
1866. Lea, Isaac.  New Unionidae, Melanidae, etc. chiefly of the United States.  Journal of the Academy of Natural Sciences of Philadelphia (New Series) 6: 113 – 187.

[20] Dr. William H. DeCamp (1825 – 1898), originally from New York, removed to Grand Rapids in 1854, served as a surgeon in the First Michigan Engineers and Mechanics Regiment 1861 – 64.  He resumed practice in Grand Rapids and was ultimately elected to the presidency of the Michigan State Medical Society.

[21] Pleurocera troostiana populations referenced in this essay:
  • Q = Newsom Springs at the Rattlesnake Saloon. 34.6481, -87.9076
  • R = Lipscomb Spring. 34.5241, -86.6013
  • S = Mechanic Branch at Sim Corder Mill.  34.9364, -87.1314
  • G = Elk River 2 km N of Kelso. 35.1395, -86.4484

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