Bengt Hubendick [1] recognized 13 valid species of lymnaeid snails in North America [2], setting aside the patelliform genus Lanx, which he did not treat. To that tally should be added L. auricularia, introduced to this continent more recently, and L. caperata, which Hubendick mistakenly synonymized under L. humilis. Oh, and subtract emarginata from Hubendick’s list, a junior synonym of L. catascopium. Is that the complete continental fauna? To Hubendick’s canonical list of 13 + 2 – 1 = 14 species of Lymnaea inhabiting the waters of North America, might be added a Number 15?
Yes. Last month [13Feb24] we reviewed the long and tortured history of Isaac Lea’s [3] nomen Lymnaea bulimoides, recognized as distinct by Hubendick but much confused by many other authorities with another of Hubendick’s canonical species, Lymnaea cubensis. We reproduced images of 23 shells in that overly long essay. I have subtracted the twelve images of L. cubensis/viator and other miscellaneous lymnaeids and re-reproduced the remaining eleven images as thumbnails in a single montage below, adding five images of related taxa I mentioned in passing last month but didn’t figure.
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| See footnote [4] for complete caption. |
Does that set of thumbnail figures look homogeneous to you? Or, just on the basis of those 16 shell images, knowing nothing about the biology of the snails that bore them, could you divide the set above into two distinct subsets? Let’s back up 118 years and get a fresh start at that question.
It will be remembered from last month’s essay that in 1906 Henry Pilsbry and James Ferriss [8] recognized four subspecies of Lymnaea bulimoides. The typical form, originally described from the Oregon Territory in 1841, is depicted in thumbnails A, B, C, K, and M. The (essentially indistinguishable) techella form, described from Texas in 1867, is depicted in thumbnails D, E, I, and O. To these Pilsbry and Ferriss added a sonomaensis form (G, P) from California, and their own brand new cockerelli (F, J, L, N), from New Mexico, Colorado, Nebraska and South Dakota. Quoting Pilsbry verbatim:
“This form (cockerelli) differs from L. bulimoides and L. techella by its more globose shape and shorter spire, and so far as we have seen is readily separable from both.”
In 1909 Pilsbry’s disciple, Frank Collins Baker [13], raised sonomaensis to the full species level and described a new Lymnaea hendersoni from Colorado, “at first thought to be sonomaensis” but “differing in the form of the spire and aperture.” And in 1911 Baker [14] published his landmark monograph on the “Lymnaeidae of North America, Recent and Fossil,” cataloging and reviewing 103 species and subspecies in 15 genera, subgenera, and groups [15], including all five of the lymnaeid taxa listed above in exhaustive detail.
The figure below is a concatenation of Baker’s [16] plate XXVII (figs 20 – 35) and plate XXVIII (figs 1 – 19). Figures 20 – 29 are Galba bulimoides (ss), figure 25 being the holotype, the same shell as figure A above. Baker identified figures 1 – 3, 8, and 30 – 35 as Galba bulimoides techella, figures 4 - 7 as G. bulimoides cockerelli, figures 9 – 11 as a new form G. bulimoides cassi, figs 12 – 14 as G. sonomaensis, figs 15 – 18 as his G. hendersoni, and fig 19 as Galba perpolita, more about which anon.
To my eye, this montage of 35 shells is as naturally and easily divisible into two sets as the montage of 16 thumbnails that opened this essay. I distinguish a set that looks like the bulimoides holotype (#25), which includes all those Baker identified as techella and cassi, and a subset with a much larger, more inflated body whorl, identified by Baker as cockerelli, sonomaensis, hendersoni, and perpolita.
Focus with me now on figs 4 – 7, depicting G. bulimoides cockerelli (three populations), and try to compare that subset of four shells with all the other (N = 23) images of shells borne by all the other subspecies of bulimoides: 1 – 3, 8 – 11, 20 – 35. I know that’s a challenge, but humor me, OK? Those two subsets clearly belong to different sets, can you see what I am saying? Why in the world would splitters as practiced in their art as Pilsbry and Baker identify the snails bearing all 27 of those shells as a single species? Especially when they split out figs 12 – 14 as a separate species sonomaensis? And figs 15 – 18 as a separate species hendersoni?
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| Baker [14] plates 27, 28. See [16] for scale. |
The answer lies in the subset of five shells boxed in red. This is a sample collected from the rural community of Bardsdale in Ventura County, CA, that weighed heavily in Baker’s calculations. He wrote, in the “Remarks” section of his treatment of cockerelli, that “Specimens from Ventura County, California, show a tendency to vary toward the techella form of shell, clearly showing that the cockerelli race is an offshoot of techella.” That sentence is phrased as though he wanted to identify the entire Bardsdale population as cockerelli, but when the time came to his assemble plates, Baker split five specimens from Bardsdale three-and-two.
Well, dang my hide. I reckon if there’s any splittin’ to be done around these parts, Sheriff Dwight Taylor is the man for the job. In 1960 Taylor teamed up with vertebrate paleontologist Claude W. Hibbard on a 223-page monograph [17] of “two late Pleistocene faunas from southwestern Kansas.” Hibbard & Taylor identified nine species of lymnaeids in the prehistoric fauna of the Great Plains, including Lymnaea stagnalis, six nominal species of Stagnicola, and two nominal species of Fossaria. And as they sorted out the Stagnicola [18], Hibbard and Taylor observed, “from a review of previous literature and on examination of specimens it appears that Stagnicola bulimoides cockerelli is specifically distinct from S. bulimoides and S. bulimoides techella.”
Taylor further observed that the geographic ranges of bulimoides and cockerelli are different (although overlapping), cockerelli being the only species to extend through the northern Great Plains, and that the “apparent lack of intergradation” where bulimoides and cockerelli do overlap (in the Southwest, for example) might be viewed with special significance. Here the young Dwight W. Taylor of 1960 seems almost to flirt with the biological species concept [19]. Taylor went on to re-identify the red-box population of cockerelli that Baker figured from Bardsdale as bulimoides techella in its entirety, and to synonymize Baker’s (1911) hendersoni under cockerelli.
And in 1973, Joe Bequaert & Walter Miller brought Taylor’s point home [20]. In their landmark “Mollusks of the Arid Southwest with an Arizona Check list,” Bequaert & Miller relayed the following report:
“R. H. Russell informs us that he found in 1969 thriving colonies of S. b. techella and S. cockerelli living together (sympatric) in the same pond at two stations in Navajo Co. (O’Haco Farm and Sitting Bull Trading Post), without transitional specimens or other evidence of interbreeding in nature.”
And indeed. Returning a second time to F. C. Baker’s red-box sample from Bardsdale. I do not agree with Taylor that the snails bearing all five of the shells boxed in red above are best identified as L. bulimoides techella. To my eye, it appears that Baker’s original identifications distinguished two distinct biological species: Figs 6 and 7 L. cockerelli and Figs. 33 – 35 L. bulimoides. The Bardsdale collection appears to have been made from a site where a pair of reproductively isolated species co-occur, just as in Arizona.
In conclusion. Lymnaea cockerelli Pilsbry and Ferriss 1906 is a distinct and valid biological species, reproductively isolated from L. bulimoides Lea 1841 and all 13 other North American species of lymnaeids. Junior synonyms of L. cockerelli include sonomaensis Hemphill 1906 and hendersoni Baker 1909. Lymnaea perpolita Dall 1905 may be a senior synonym.
Yes, dang my hide, again. Look back with me at Figure 19 on the plate of shells I concatenated from Baker [14] above. That is an image that Baker borrowed from William Healy Dall’s 1905 monograph on the land and freshwater mollusks collected by the 1899 Harriman Expedition to Alaska [21]. On his pages 78 – 79 Dall described a single “small, translucent, dark amber color” shell collected at Nushagak, Bristol Bay, Alaska as Lymnaea (Stagnicola?) perpolita n. sp. It really looks to me like Dall may have scooped Pilsbry and Ferriss by one year.
But as far as I can tell, Dall’s nomen perpolita has almost never [22] been applied to any other population of snails ever collected again, while Pilsbry and Ferriss’ cockerelli has seen wide use throughout western North America. Forget that you read these last two paragraphs. I never wrote them.
So to summarize, over last month’s essay and this month’s as well. Isaac Lea’s (1841) nomen Lymnaea bulimoides has been applied to populations of at least three distinct biological species, including cubensis/viator and cockerelli as well to as to the bona fide bulimoides of “Oregon” as originally described. The eastern extent of the L. bulimoides range has been overstated. My buddy Bruce Stephen and I have not been able to confirm populations of bona fide L. bulimoides anywhere in Kansas, Nebraska, or The Dakotas. Populations of both L. cubensis/viator and L. cockerelli are not uncommon in those states, however.
Then opening the Burch Bible [12] to pages 172 – 174 we find five (full) species listed under Fossaria (Bakerilymnaea), the subgenus set aside for crappy little amphibious lymnaeids with bicuspid first laterals. Under the first of those species, Fossaria (Bakerilymnaea) bulimoides, we find six subspecies. In the table above I have listed those 12 taxa together with our modern FWGNA understanding of their identities. For the time being. Additional data would be most welcome.
Notes:
[1] Hubendick, B. (1951) Recent Lymnaeidae. Their variation, morphology, taxonomy, nomenclature and distribution. Kungliga Svenska Vetenskapsakademiens Handlingar Fjarde Serien 3: 1 - 223.
[2] Hubendick listed three species as Holarctic: stagnalis, truncatula, and “palustris,” by which he was referring to populations better identified as elodes here. As unique to North America, he listed ten: humilis, cubensis, bulimoides, catascopium, emarginata, columella, megasoma, haldemani, arctica and “utahensis (?)” I would add a second question mark behind utahensis. In fact, I’m not 100% sold on haldemani.
[3] Lea, Isaac (1841) On fresh water and land shells (continued). Proceedings of the American Philosophical Society 2(17): 30 – 34.
[4] Original identification and authority for the 16 shells depicted, with standard length if it is known or can be estimated: (A) Lea’s bulimoides holotype 9.3 mm, (B) bulimoides from Haldeman [5], (C) bulimoides from Binney [6], (D) techella from Haldeman [7], (E) techella from Pilsbry [8] 13.0 mm, (F) cockerelli from Pilsbry [8] 10.0 mm, (G) sonomaensis from Pilsbry [8] 10.0 mm, (H) vancouverensis from Baker [9] 18.5 mm, (I) techella from Clarke [10] 10.6 mm, (J) cockerelli from Clarke [10] 5.5 mm, (K) bulimoides from Clarke [10] 12.0 mm, (L) cockerelli from Leonard [11], (M) bulimoides from Burch [12] 13.8 mm, (N) cockerelli from Burch [12] 13.8 mm, (O) techella from Burch [13] 13.1 mm, (P) sonomaensis from Burch [12] 6.9 mm.
[5] Haldeman, S.S. (1844) A monograph of the freshwater univalve Mollusca of the United States, Number 7 Philadelphia: Cary & Hart, Dobson, and Pennington. 32 pp, 4 plates.
[6] Binney, W.G. (1865) Land and fresh water shells of North America Part II, Pulmonata Limnophila and Thalassophila. Smithsonian Miscellaneous Collections 143: 1 – 161.
[7] Haldeman, S.S. 1867 Description of a new species of Limnaea. American Journal of Conchology 3: 194.
[8] Pilsbry, H.A. and J.H. Ferriss (1906) Mollusca of the southwestern states II. Proceedings of the Academy of Natural Sciences of Philadelphia 58: 123 – 175.
[9] F. C. Baker’s brief (1939) description of Stagnicola bulimoides vancouverensis nov. var. was published in The Nautilus 52(4): 144. The figure reproduced above followed in Nautilus 53(1) plate 7.
[10] Clarke, A. (1973) The freshwater molluscs of the Canadian Interior Basin. Malacologia, 13, 1-509.
[11] Leonard, A.B. (1959) Handbook of Gastropods in Kansas. Miscellaneous Publications of the University of Kansas Museum of Natural History 20: 1 – 224.
[12] 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 that 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).
[13] Baker, F.C. (1909) A new species of Lymnaea. The Nautilus 22: 140 – 141.
[14] Baker, F.C. (1911) The Lymnaeidae of North and Middle America, Recent and Fossil. Chicago Academy of Sciences, Special Publication Number 3. 539 pp.
[15] Note that the number of genera, subgenera, and other higher-level "groups" recognized by Baker in the North American Lymnaeidae is exactly the number of valid biological species. This is not a coincidence.
[16] Quoting the caption to Plate XXVII, Figs 20 – 35 were “enlarged about two diameters” at their reproduction, and on that basis I have added the red scale bar. Figs 1 – 19 were mostly “enlarged 2 diameters” on their original plate XXVIII, with the exceptions of figs 12 – 14 “enlarged about three diameters,” and fig 19, “1.5 diameters.”
[17] Hibbard, C.W. and D.W. Taylor (1960) Two late Pleistocene faunas from southwestern Kansas. Contributions from the Museum of Paleontology, University of Michigan 16(1): 1 – 223.
[18] Yes, Dwight Taylor considered L. bulimoides to be a little Stagnicola, not a big Galba/Fossaria. F.C. Baker made exactly the same judgement call in 1939, see footnote #17 of last month’s essay. This is yet further support, if any is needed, for Hubendick’s [1] opinion that there is insufficient morphological basis for the recognition of genera within the family Lymnaeidae. The FWGNA follows Hubendick in assigning all North American lymnaeids (except the patelliform genus Lanx) to the typical genus Lymnaea, adding (subgenera) for their indexing function alone. We do not assign Lea’s bulimoides to Lymnaea (Galba) to transmit any hypothesis of evolutionary relationship whatsoever, but only because “Galba” seems to connect with the greatest fraction of the recent literature.
[19] I never met the reclusive millionaire Dwight Taylor, but the dark shadow he cast over freshwater and terrestrial malacology extended far beyond the American West. Well, even a sundial facing west will be right once a day.
[20] Bequaert, J. & W. Miller (1973) The Mollusks of the Arid Southwest, with an Arizona Check List. Tucson: University of Arizona Press.
[21] Dall, W. H. (1905) Land and fresh water mollusks of Alaska and adjoining regions. Smithsonian Institution Harriman Alaska Series 13: 1 – 171.
[22] My search of the iDigBio database [23] for family = Lymnaeidae and species = perpolita returned 12 hits in the USNM from Alaska and two hits in the University of Alaska Museum from Iceland. Very little data on any of the 14 – not even dates of collection for the USNM records.
[23] For more about iDigBio, see:
- 20 Years of Progress in the Museums [22May19]