Fun with Campeloma!

Editor’s Notes: The essay that follows is the third in a three-part series on the systematics and taxonomy of viviparid gastropods.  I’d recommend that you back up and read my essays of [9Mar21] and [5Apr21] before going forward, if you haven’t already.

It was subsequently published as: Dillon, R.T., Jr. (2023c)  Fun with Campeloma!  Pp 97 – 110 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Hey boys and girls!  Want to match wits with an international team of 16 professional scientists?  Click the picture below and download our keen quiz #1!

The figure shows representative shells from the six species of North American Campeloma sequenced by Dr. Björn Stelbrink and his colleagues for their worldwide viviparid gene tree [1].  If you click it, you can download a pdf circular that also reprints the Burch/Vail dichotomous key [2] that Dr. Björn and his team used to identify the snails that bore those six shells.  How many can you get right?  The answers were hidden in our March essay, posted [9Mar21].

Keen Campeloma Quiz #1

So now kids, do you think you’ve got what it takes for an exciting career in the fast-growing field of freshwater gastropod Malacology?  Are you looking for a role model?  Look no further than the example set by our colleague Dr. Steven G. Johnson, currently Dean of the College of Science at the University of New Orleans [3].  The 13 papers he published on the evolutionary biology of Campeloma 1992 – 2007 are as good as any body of work on any malacological topic anywhere, ever.  I’ve listed my favorites at footnote [4] below.

Over that 16-year period, Dr. Steve brought a variety of techniques – allozyme electrophoresis, flow cytometry, mtDNA sequencing – to bear on the evolutionary relationships among dozens of populations of Campeloma, initially sampled throughout the eastern US, then subsequently focused on a sweeping arc of Atlantic and Gulf drainages from South Carolina to Louisiana.  He documented, quite thoroughly and beautifully, multiple origins of parthenogenesis in these populations – sometimes spontaneously by autodiploidy and sometimes by allotriploidy, through hybridization and backcrossing.

The grayscale background of the figure below shows the study area for a 1999 paper that Dr. Steve published with Eric Bragg [4].  He assigned these particular 31 Campeloma populations [5] to five specific nomina using the same Burch/Vail dichotomous key that you used for Keen Quiz #1, with an eye toward type localities.  So populations inhabiting the Wekiva River drainage must be C. floridense by definition, and populations inhabiting the Ochlockonee must be C. parthenum.  Campeloma limum was described from South Carolina, so that name would be appropriate for Atlantic drainages, and C. geniculum was described from the Flint River, so appropriate for Gulf drainages [6].  The assignment of Say’s specific nomen Campeloma decisum to populations west of the Mobile Basin was a vanilla call, by shell only.

It is interesting to notice that at no point in no body of water ever sampled by Dr. Steve Johnson during his entire 16 year career did more than a single nominal species of Campeloma occur sympatrically.  Where (sexual) C. limum populations and (sexual) C. geniculum populations have apparently come into contact, he found parthenogenic populations which he identified by a third name, C. parthenum.

Johnson & Bragg Fig 1, Stelbrink mapped in red

So, Johnson & Bragg sequenced the mitochondrial cytB gene for 1 – 5 snails sampled from each of these 31 populations.  Their mtDNA gene tree (maximum parsimony) showed six distinct C. parthenum sequences (and one for C. floridense) scattered haphazardly inside a large C. limum cluster, with C. geniculum on one outside branch and C. decisum on another.  Nominal decisum and nominal geniculum are apparently separated by a big, beautiful discontinuity of some sort at the Mobile Basin, but Dr. Steve’s data did not address whether that barrier is reproductive or merely geographical.

Which brings us back to Dr. Björn Stelbrink’s study of worldwide viviparid phylogeny with which we kicked off this essay [1].  Because Dr. Björn’s little sample of six nominal Campeloma species, marked in red on the map above, was centered on the Mobile Basin and North Alabama, right where Dr. Steve Johnson mapped his mysterious discontinuity.  And although Dr. Björn’s group only analyzed single snails from single populations for each of those six species in the old-school U1S2NMT3 gene tree we reviewed in March, reference back to his team’s supplementary table S1 reveals that sometimes they actually sequenced two.

So the map above shows samples from two populations of C. decisum, two populations of C. decampi, and two populations of C. regulare, as well as singletons for parthenum, geniculum and limum.  All nine of these individual snails were identified using the same Burch/Vail key everybody has used for 40 years and sequenced for three genes [7].  And this suggests a test.

If the morphological characters upon which the Burch/Vail key was based fairly reflect the evolutionary history of the Campeloma populations which bear those shells on their backs, one would expect the two snails that Dr. Björn identified as decisum1 and decisum2 to be the most similar to each other genetically, and ditto for the two snails identified as decampi1 and decampi2, and ditto for regulare1 and regulare2.

The figure below is a simple neighbor-joining network generated by the software inside GenBank, connecting the nine CO1 sequences deposited by Dr. Björn Stelbrink for his six nominal species of Campeloma, with the nearest neighbor for each of the six test snails identified by a red arrow.

Of the six nearest-neighbors, only one matched correctly.  The nearest neighbor of decisum1 was in fact decisum2 (98.5% sequence identity).  But oddly, the nearest neighbor of decisum2 was not decisum1, but rather decampi2, with which it demonstrated 99.1% identity.  And further, the nearest neighbor of decampi2 was not decampi1 (by a long shot), but mutually with decisum2.  The nearest neighbor of decampi1 was decisum1, as was the nearest neighbor of regulare1 as was the nearest neighbor of regulare2.  In fact, of the six CO1 sequences obtained for nominal species pairs, only the one sequence, that of decisum1, correctly matched its sister.

Neighbor-joining network from Stelbrink [1] COI sequences

Turning now to the two nuclear genes sequenced by Dr. Björn’s team, very little variance was apparent among the nine sequences for either, none correlating with the taxonomy.  In the histone H3 data set (328 bp), the pair of decisum sequences matched each other and the singleton parthenum sequence.  That group of three differed by a single A/G transition at position 262 from a group that contained both decampi sequences and both regulare sequences.  The limum sequence and the geniculum sequence were both a bit more distinctive, differing from each other (and from the decisum group) by four transitions.

For 28S data set (1,058 bp) the two decisum sequences were again identical to each other, to the parthenum, and to one of the regulare.  The other regulare differed by a single A/G transition at residue 535 and the geniculum differed by a single C/T transition at residue 833.  The two decampi were also again identical to each other and (this time) to the single C. limum sequence.  That set of three differed from the decisum cluster by a two-nucleotide indel at positions 835-6, which is surprising, especially given the geography, and I think significant.  There most certainly is some genetic structure to this set of 3x9 DNA sequences, but the 19^th-century taxonomy is not capturing it.

Hey kids, are you ready for some more fun?  Now’s the time to try Keen Quiz #2, shown on page 3 of that same pdf circular you downloaded at the beginning of this essay.

Can you find the three secret-decoder Campeloma hidden in the weeds?  Now can you identify those three shells using the Burch/Vail key?  Circle each shell and write what you think it is in the spaces provided.  Answers below, no peeking!

Not uncommonly, when I am casting about for larger analogies to apply to the messy evolutionary biology of freshwater gastropods, I find myself looking toward the botanical, rather than to the zoological [8].  And in the case of North American Campeloma, I have found inspiration in the dandelions.

Keen Campeloma Quiz #2

The reproductive biology of dandelions is as diverse as one could possibly imagine – outcrossing, selfing, parthenogenetic cloning, sexual/asexual cycling, everything.  An elaborate taxonomy built up in nineteenth-century Europe to describe all the morphs, forms, subspecies and sections of dandelions, but today, most botanists refer the entire yellow-blooming, blowball-sprouting mess to Taraxacum officinale, because after a couple hundred years of squinting at them and screwing around with them, all dandelions pretty much look alike.

The widespread incidence of parthenogenesis in North American populations of the viviparid genus Campeloma voids the biological species concept and necessitates a retreat to the morphological.  And since (judging from the work of Johnson and Stelbrink) there are apparently no consistent phenotypic characters, shell morphological or otherwise, by which Campeloma populations can be distinguished, the FWGNA Project will refer all populations of Campeloma to the oldest available specific nomen, Campeloma decisum (Say 1817).

But how about inconsistent characters?  Nothing in the paragraph above should be interpreted as foreclosing the recognition of C. decisum subspecies – geographically separate and morphologically different forms – even if they intergrade, even if there is no genetic basis for the distinction [9].  The shell morphology of Campeloma populations most certainly does vary regionally.  Indeed, big rivers of the American interior are often inhabited by populations of Campeloma bearing distinctly heavy shells, which have traditionally been identified as C. crassulum Rafinesque 1819, almost certainly a case of cryptic phenotypic plasticity [10].  The FWGNA Project recognizes these populations at the subspecific level, as C. decisum crassulum, just as we recognize heavily-shelled Pleurocera canaliculata canaliculata in those same big rivers, and more gracile P. canaliculata acuta in the little streams that feed into them.

And certainly Call’s (1886) floridense could be saved as a subspecies name for C. decisum with brown apertures, right?  And Binney’s (1865) decampi also seems a likely candidate for retention at the subspecies level.  Although I have no personal observations to contribute, the figures and photos I have seen (e.g., shell #1 way up above) seem to suggest that Campeloma populations in North Alabama may indeed bear shells that are atypically slender and higher-spired, likely for ecophenotypic reasons we do not understand.  And the nomen “decampi” has appeared in recent literature connected to some conservation concerns [12].

As we have often pointed out when faced with analogous situations in the North American pleurocerids, the Latin nomina assigned to biological populations may bear an important indexing function, as well as evolutionary significance.  So, in addition to crassulum and floridense and (perhaps) decampi, it would be a shame to see the names that Dr. Steve Johnson used for his important works – geniculum (Conrad 1834), limum (Anthony 1860), and parthenum Vail 1979 – forgotten by the google machine.  Those names have been useful to index Campeloma populations across the southeastern United States for quite a few years now.

But here’s a big problem, kids.  And maybe you can help!  Let’s look at how you did on Quiz #2.  Those secret-decoder shells didn’t have brown apertures, did they, so they are not floridense.  Did you think that their whorls have angled shoulders, or are their shoulders rounded, or do they have no shoulders at all?  Angled?  So are those shells broadly ovate or narrowly ovate?  Are they Campeloma limum?  Campeloma geniculum?  Did any of you guess Campeloma decisum for any of the secret-decoders?

Surprise!  All three of the shells hidden in the dandelion patch above are topotypic Campeloma decisum, collected from a pond in Philadelphia’s Fairmount Park, along the banks of the Schuylkill River, where Thomas Say almost certainly explored in 1817.  The snails that bore those three shells were C. decisum, by definition.

That makes them what scientists call a “control,” and what kids like us call super-duper secret-decoders.  Every other Campeloma population, bearing every other shell shape, form, or size, that anybody has ever seen, are (scientifically-speaking) unknown.  That includes all nine of those populations identified by Dr. Björn Stelbrink’s team we had fun with in Keen Quiz #1, and all 31 of those populations studied by Dr. Steve Johnson.  If Dr. Björn’s shells and Dr. Steve’s shells look like the secret-decoders, their correct identification is C. decisum, by definition.  Only if they look different, can they be identified as anything else.

Did Jack Burch and Virginia Vail look at secret-decoders first, when they were making their 1982 dichotomous key?  I don’t know.  The University of Michigan Museum of Zoology does (indeed) hold a couple lots of Campeloma decisum collected from the Schuylkill River in Philadelphia, so it is possible.  But I don’t know about you, kids, I cannot make the Burch/Vail key work at all.  I get messed up early, way up at couplet 14, because I really think that at least some of our secret-decoder shells demonstrate “angled” shoulders, which sends me down the wrong path.

So it would be great to save Dr. Steve Johnson’s limum, geniculum, and parthenum as subspecies names, it really would.  But even setting aside the Burch/Vail key, I cannot distinguish limum collected from its type locality (“South Carolina”) and control decisum from Philadelphia.  Could I distinguish geniculum or parthenum from decisum/limum?  I don’t know that, either [13].  I don’t have control collections from the Flint River or Lake Talquin, or really anywhere in the Gulf drainages of Georgia and Florida.

Boys and girls, I’m going to leave this challenge to you all, the next generation of malacologists. Here’s what I want you to do.  Mail your completed quiz sheets to “Fun With Campeloma,” P.O. Box 31532, Charleston, SC 29417.  Don’t forget to include your name and address and $1.25 for postage and handling.  No, I won’t grade them – I don’t know the right answers myself.  But all entries will be entered into a random drawing.  And one lucky winner will get a genuine FWGNA deputy’s badge and a license to classify the subspecies of Campeloma decisum throughout North America any way he or she wants.

But one last warning, kids, before we sign off this month.  You may hear some grown-ups asking why we have to fall back to an 18^th century morphological species concept, as I so boldly asserted ten paragraphs above.  Accepting that the biological species concept is void for Campeloma, those grown-ups may be suggesting that we move forward to the phylogenetic species concept, or one of those other recent concepts based on gene trees.  Don’t all the genetic data we have reviewed this month suggest some sort of evolutionary structure to these populations?  Surely all the Campeloma populations spread across half of North America aren’t equally related to each other, are they?  DNA sequences and fancy tree-generating algorithms are a more scientific way to name snail populations than some kid’s subjective judgement calls on fat brown shells, right?

Be careful around grown-ups like that, boys and girls!  They’re not malacologists, they’re phylogenetic systematists!  We’re going to learn a lot more about phylogenetic systematics in the next few months, and why ideas like that don’t hold water.  So stay tuned!

Notes:

[1] Stelbrink, B., R. Richter, F. Köhler, F. Riedel, E. Strong, B. Van Bocxlaer, C. Albrecht, T. Hauffe, T. Page, D. Aldridge, A. Bogan, L-N. Du, M. Manuel-Santos, R. Marwoto, A Shirokaya, and T. Von Rintelen (2020)  Global diversification dynamics since the Jurassic: Low dispersal and habitat-dependent evolution explain hotspots of diversity and shell disparity in river snails (Viviparidae).  Systematic Biology 69: 944 – 961.

[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] Rule #1 is, stay out of museums! Those musty cabinets of dusty shells will kill your scientific career faster than a confession of the Apostle’s Creed.  And Rule #2 is, never return emails from anybody who ever has.

[4] Johnson, S. G. 1992. Spontaneous and hybrid origins of parthenogenesis in Campeloma decisum (freshwater prosobranch snail). Heredity 68:253-261.  Johnson, S.G., R. Hopkins, and K. Goddard. 1999. Constraints on elevated ploidy in hybrid and non-hybrid parthenogenetic snails. Journal of Heredity 90: 659-662.  Johnson, S.G. and W. Leefe. 1999. Clonal diversity and polyphyletic origins of hybrid and spontaneous parthenogenetic Campeloma (Gastropoda: Viviparidae) from the southeastern United States. Journal of Evolutionary Biology 12:1056-1068.  Johnson, S.G. and E. Bragg. 1999. Age and polyphyletic origins of hybrid and spontaneous parthenogenetic Campeloma (Gastropoda: Viviparidae) from the southeastern United States. Evolution 53:1769-1781.  Johnson, S.G. 2000. Population structure, parasitism and survivorship of sexual and parthenogenetic Campeloma limum (Gastropoda: Viviparidae). Evolution 54:167-175.  Johnson, S. G., 2005. Mode of origin differentially influences the fitness of parthenogenetic freshwater snails. Proc. Roy. Soc. Lond. B. 272: 2149-2153.  Johnson, S. G. 2006. Geographic ranges, population structure and ages of sexual and parthenogenetic snail lineages. Evolution 60:1417-1426.

[5] The 1999 paper by Johnson with W. R. Leefe surveyed 55 populations.  The Johnson & Bragg paper from which the figure was extracted retained the Johnson & Leefe numbering system but focused on a slightly-less-cluttered 31-population subset.

[6] Johnson never sampled the Flint River proper, up in Georgia, where it comes in close contact with the Ocmulgee R., which drains east to the Atlantic.  This would certainly have been intellectually fascinating, and might well have clarified Campeloma taxonomy substantially, and the omission drives me nuts, absolutely nuts.

[7] The Stelbrink team sequenced mitochondrial CO1 and nuclear 28S and H3.  They did not (alas) sequence mitochondrial cytB, so their data cannot be integrated with that of Steve Johnson.

[8] The most obvious example is my “USR” model for life history evolution in the freshwater mollusks, which I patterned after J. P. Grimes” CSR model for the plants: Competitors, Stress-tolerators, and Ruderals.  That idea was the unifying theme of my (2000) book for Cambridge University Press.  I thought it would make me rich and famous.  I wonder why not.

[9] To refresh your memory on the definition of the word, “subspecies,” see:

• What Is a subspecies? [4Feb14]
• What Subspecies Are Not [5Mar14]

[10]  Quoting Dillon and colleagues [11], “phenotypic plasticity may be considered cryptic when intrapopulation morphological variance is so extreme as to prompt an (erroneous) hypothesis of speciation.”  To refresh your memory:

• Pleurocera acuta is Pleurocera canaliculata [3June13]
• Pleurocera canaliculata and the process of scientific discovery [18June13]
• Elimia livescens and Lithasia obovata are Pleurocera semicarinata [11July14]

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

[12] Haggerty, T.M. and J.T. Garner (2008)  Distribution of the armored snail (Marstonia pachyta) and slender Campeloma (Campeloma decampi) in Limestone, Piney, and Round Island Creeks, Alabama.  Southeastern Naturalist 7: 729-736.  Haggerty, T.M., J.T. Garner and L. Gilbert (2014)  Density, demography, and microhabitat of Campeloma decampi (Gastropoda: Viviparidae). Walkerana 17: 1 – 7.

[13] But reading all the way down through the Burch/Vail key to couplet #19, one gets the strong impression that even Virginia Vail could not distinguish her Campeloma parthenum from Campeloma decisum.  The basis for the decisum/parthenum distinction is geographical only.  If you find it in the Ochlockonee River, it’s parthenum.  Otherwise, it’s decisum.  So parthenum is an allotriploid hybrid of nominal limum and geniculum, which Burch/Vail distinguished from decisum/parthenum by that problematic shoulder-shape couplet #14?   So two nominal species with angled shoulders hybridize to form populations with rounded shoulders?  Hmmm.  That’s as far down this rabbit hole as I care to go, even in a discursive footnote.

Bill and Ruth and Jack and Virginia, and Campeloma

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Bill and Ruth and Jack and Virginia, and Campeloma.  Pp 85 – 95 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Bill Clench was already well into the mascot phase of his career when I first met him at the 1976 AMU meeting in Columbus, Ohio.  Colleagues, students, and friends ushered him front-row-center for the annual society photo, Joe Morrison [1] and Leslie Hubricht [2] trailing in his wake.  I found Dr. Clench to be a warm and outgoing gentleman, still alert at age 78.  Please Lord, take me home before anybody calls me “alert.”

William J. Clench was born in New York in 1897 and grew up in the Boston area, collecting bugs, snails and shells around the Fenway, the Blue Hills and the local beaches [3].  Charles W. Johnson, the noted marine malacologist at the Boston Society of Natural History, was an early influence.  Clench graduated from Michigan State University in 1921, earned his MS at Harvard in 1923, then moved on to the University of Michigan to work on his doctorate [4], where Bryant Walker, quoting Tucker Abbott’s remembrance [5], “lit the malacological fires within Bill and was largely responsible for his first love, the freshwater mollusks.”

American Malacological Union 1976 [6]

From Michigan Clench accepted the mollusk curatorship at Harvard’s Museum of Comparative Zoology, where he served for 40 years, 1926 – 1966, mentoring many students who would become quite influential themselves.  Clench’s most famous student was R. Tucker Abbott, who succeeded Henry Pilsbry as curator at the ANSP and editor of The Nautilus, but we should not fail to mention the unionid guys Dick Johnson and Sam Fuller, or Arthur Clarke, whose landmark work on the Canadian freshwater molluscan fauna [7] sits handy by my desk, here 40 years after its publication.

Clench’s bibliography lists 420 scientific papers, covering the breadth of malacology: marine, terrestrial, freshwater and fossil, focused on North America but ultimately worldwide [8].  Most of his better papers were coauthored by Ruth Turner, another former student, with whom Clench’s life was “entwined,” to borrow Dick Johnson’s carefully-chosen verb.  We have previously featured on this blog the 1956 Clench and Turner monograph on the freshwater mollusks of Florida/Georgia Gulf drainages [9], which was an important contribution.

Clench’s malacology was early-modern, rooted in the old typology but with a growing appreciation of genetic variation within and among populations.  Looking down from my 2021 freshwater-gastropod-centric perspective, his greatest contribution was his two-part series on the North American Viviparidae, published in 1962 [10] and (with Sam Fuller) in 1965 [11].

The taxonomic history of the North American Viviparidae is identical to the taxonomic history of the North American Pleuroceridae, minus one order of magnitude coming into the 20^th century, and two going out [12].  Digging through the musty tomes on the shelves and the dusty shells in the cabinets of the MCZ in the early 1960s, Clench was able to uncover 49 Latin nomina assigned to the genus Campeloma, Isaac Lea [14] tying C.S. Rafinesque for the lead with six each.  Of those 49 nomina, 35 he discarded for cause or synonymized, little rationale given or expected, at the close of the era when such good works were still possible.  Clench did not preface his work with an exhaustive study of shell morphological variation, as did my hero Calvin Goodrich for the North American pleurocerids in the 1940s [15].  But I don’t think he missed any viviparid nomina either, as Goodrich simply skipped hundreds of pleurocerids.  I think Clench got them all.  Thank you, Bill.

Alas, Clench did not explain why he spared the 14 specific Campeloma nomina that survived his 1962 monograph, any more than he explained why he cut the other 35.  That burden was shouldered 20 years later by Dr. John B. Burch [16], with an obscure contribution from Dr. Virginia A. Vail.

From the Burch/Vail key [16]

The “Family Viviparidae” header in Burch’s dichotomous key, way back on page 227, carries an asterisk.  And at the bottom of page 227 is printed, “*From Burch & Vail (1982).”  But no work by Burch & Vail is listed among the references, nor was one ever published subsequently, to my knowledge [17].

Burch’s bibliography does, however, list six papers published by Virginia Vail at that point in her career, all solo, and they are good ones.  She was an excellent scientist, about whom I have been able to discover little.  She was born in Schenectady, NY, in 1945, earned her B.A. at Hartwick College (NY) and her M.S. and Ph.D. at Florida State University, graduating in 1975 [18].  From thence Vail went directly to the Tall Timbers Research Station north of Tallahassee, where she spent the rest of her career.

In 1977 and 1978 Virginia Vail published a two-part series comparing the reproductive anatomy and life history of Campeloma, Lioplax, and Viviparus in Florida.  Her first paper [19] was anatomical, featuring very nice drawings of male and female reproductive systems for all three taxa, and her second paper [20] ecological, detailing seasonal reproductive cycles.  The viviparids are quite conservative anatomically; Virginia was able to document only negligible difference in the plumbing of the three genera [21].  But here 40 years later, we still await a finer contribution to the comparative biology of the North American Viviparidae.

Virginia Vail identified the Campeloma population she selected for her study as C. geniculum (Conrad).  Interestingly, that particular population, inhabiting the Chipola River about 60 miles NW of Tallahassee, seems to have been entirely sexual, males and females (apparently) in roughly equal proportion.  She made only passing reference to asexual reproduction in her 1977-78 papers, noting that Mattox [23] had documented parthenogenesis in Campeloma rufum [24] as early as 1937.

Vail [19] figs. 5 & 10 [25]

The next year, Vail described Campeloma parthenum from Lake Talquin, an impoundment of the Ochlockonee River west of Tallahassee.  She distinguished that population both by its apparent absence of males and by the contour of the outer lip of the shell [26].  But she seems to have been struggling with species concepts, even as she was describing new ones.  Here is the title and abstract of the talk she gave at the August 1979 meeting of the American Malacological Union in Corpus Christie, TX:

“CHAOS IN THE GENUS CAMPELOMA (GASTROPODA: VIVIPARIDAE)

A poor understanding of environmentally induced shell variation, anatomical characteristics and the animal’s biology makes species identification difficult.  The occurrence of both dioecious and parthenogenetic populations (races? species?) and their peculiar geographic distributions further complicate the problem.  Observations on southeastern populations are offered to illustrate the problem and suggest solutions.”

I could not have said that better myself.  Fascinatingly, this was neither the title nor the abstract ultimately published in the Bulletin of the American Malacological Union for 1979, page 67.  The version that saw print was much more tamely entitled, “The Species Problem in Campeloma,” and featured a relatively measured critique of reliance on shell character, noting “the fact that reproduction can occur either parthenogenetically or sexually.”  As of the publication of her 1979 abstract, Virginia Vail was only counting two Campeloma species in Florida and Georgia combined, C. geniculum and “C. limum (includes C. floridense).”

I seem to remember [27], here 40 years later, that the solution Virginia Vail suggested on that August morning at La Quinta Royale Hotel in Corpus Christie, TX, recognized just those two species, a heavily-shelled C. geniculum (sexual) and more lightly-shelled C. limum (parthenogenetic).  That was certainly the direction Fred Thompson was tending by the 1990s with his “Identification Manual for The Freshwater Snails of Florida [30].”  Thompson listed four Campeloma species for The Sunshine State (geniculum, limum, floridense and parthenum), but observed, “in view of the inconsistency of shell characters, these last three forms may represent only a single species, Campeloma limum.”

American Malacological Union 1979

But returning to the thread of our story.  It was sometime during the late 1970s that Jack Burch signed a contract with the EPA to deliver his illustrated key to the North American Freshwater Snails [16].  And somehow [31] he linked up with Virginia Vail, during the full flower of her career.

The Burch/Vail key to the North American Viviparidae that ultimately saw publication in 1982 proceeds unremarkably through its first ten couplets, guiding us to the genus Campeloma on page 228, where we are referred to supplemental note (4).  That endnote – on page 268 now – begins with a brief review of Clench’s signal (1962) contributions to our understanding of the genus Campeloma [10].  Then four more nomina are subtracted from Clench’s list of 14 species on the authority of Arthur Clarke [32]: leptum Mattox 1940, tannum Mattox 1940, integra (Say 1821) and milesi (Lea 1863).  That brought our continental fauna down to 10.

Returning to the main key, on page 229, we find an earnest effort to distinguish, by shell morphology alone, eight species of Campeloma.  Three of the ten species surviving Burch’s endnote (4) did not survive the perilous transfer forward from page 268 to page 229.  The specific nomina brevispirum (Baker 1928), exilis (Anthony 1860), and gibba (Currier 1867) seem to have vanished [33].  But one brand new species of Campeloma was added, Vail’s [26] parthenum, bringing our total continental Campeloma fauna to N = 8 canonical species, as of 1982.  In the order of their description:

• Limnaea decisa Say 1817.  Clench speculated “Delaware River?”
• Campeloma crassula Rafinesque 1819.  The Ohio.
• Paludina genicula Conrad 1834.  Flint River, GA.
• Paludina regularis Lea 1841. Coosa R, AL.
• Paludina lima Anthony 1860. South Carolina.
• Melantho decampi Binney 1865. Decatur, AL. [34]
• Campeloma floridense Call 1886.  Wekiva River, FL.
• Campeloma parthenum Vail 1979.  Lake Talquin, FL.

The Burch/Vail key to the Campeloma begins with aperture color (white vs brown), then moves on to shell shoulders (angled vs rounded) then moves on to shell profile (broadly ovate vs narrowly ovate), and so forth.  It is a valiant effort, and I do not mean to diminish the contribution of its authors.  Just the opposite.

Science is the construction of testable hypotheses about the natural world.  It is not about being right, it is about being testable.  The Burch/Vail dichotomous key to distinguish the eight canonical species of North American Campeloma is science.

Next month, we test it.

Notes

[1] For my remembrance of J.P.E. Morrison, see:

• Joe Morrison and the Great Pleurocera Controversy [10Nov10]

[2] For a bit more about Leslie Hubricht, see:

• The Most Cryptic Freshwater Gastropod in the World [6Aug17]

[3] Most of the biographical details relayed above were gleaned from: Turner, R. D. (1985)  William J. Clench October 24, 1897 – February 22, 1984.  Malacological Review 18: 123-124.

[4] Surprisingly, Clench did not finish.  He was ultimately awarded honorary doctorates from both Michigan and MSU in 1953.

[5] Abbott RT (1984). "A Farewell to Bill Clench". The Nautilus 98 (2): 55–58.

[6] This is a detail from a scan of the original 8x10 glossy in my files.  The back is stamped, “Dept. of Photography & Cinema, The Ohio State University,  No. 191231-1, Please Give Credit”  Done.

[7] Clarke, A.H. (1981) The Freshwater Mollusks of Canada. Ottawa: The National Museums of Canada.

[8] Johnson, R.I. (2003)  Molluscan taxa and bibliographies of William James Clench and Ruth Dixon Turner.  Bulletin of the Museum of Comparative Zoology at Harvard College 158: 1- 46.

[9] Clench, W.J. & R.D. Turner (1956)  Freshwater mollusks of Alabama, Georgia, and Florida from the Escambia to the Suwannee River. Bull. Fla. State Mus. (Biol. Sci.), 1: 97-239.   For more, see:

• Fred Thompson, Steve Chambers, and the pleurocerids of Florida [15Feb17]

[10] Clench, W.J. (1962) A catalogue of the Viviparidae of North America with notes on the distribution of Viviparus georgianus Lea. Occasional Papers on Mollusks 2(27): 261-287.

[11] Clench, W.J. & S.L.H. Fuller (1965) The genus Viviparus (Viviparidae) in North America. Occasional Papers on Mollusks 2(32): 385-412.

[12] Graf [13] has catalogued “nearly 1,000” specific nomina historically applied to North American freshwater gastropods of the family Pleuroceridae.  Between 1934 – 1944 my hero Cavin Goodrich was able to pare these down to approximately 150.  For more, see:

• The Legacy of Calvin Goodrich [23Jan07]

[13] Graf, D. L. (2001) The cleansing of the Augean Stables, or a lexicon of the nominal species of the Pleuroceridae (Gastropoda: Prosobranchia) of recent North America, north of Mexico. Walkerana 12 (27) 1 - 124.

[14] For more about the “Nestor of American Naturalists,” see:

• Isaac Lea Drives Me Nuts [5Nov19]

[15] For the further exploits of my hero, see:

• Goodrichian Taxon Shift [20Feb07]
• Mobile Basin II: Leptoxis Lessons [15Sept09]
• CPP Diary: The Spurious Lithasia of Caney Fork [4Sept19]

[16] 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).

[17] The parallel between the careers of Virginia Vail and George Te is inescapable here.  George Te was a Burch student in the late 1970s and seems to have ghost-written Burch’s entire treatment of the Physidae, as Virginia Vail ghost-wrote the Viviparidae.  For more on George Te, see:

• To Identify a Physa, 1975 [6May14]
• To Identify a Physa, 1978 [12June14]

[18] Abbott, R.T. (1975)  American Malacologists, Supplement.  American Malacologists, Greenville, Delaware. 

[19] Vail, V.A. (1977)  Comparative reproductive anatomy of 3 viviparid gastropods.  Malacologia 5: 519 – 540.

[20] Vail, V.A. (1978)  Seasonal reproductive patterns in 3 viviparid gastropods.  Malacologia 6: 73 – 97.

[21]  The viviparids have evolved [22] quite a few unique adaptations that separate them from all other living gastropods, including a weird operculum and even weirder radula.  The right tentacle of the male has been modified into a simple, external penis and the pallial gonoduct of the female modified into a marsupium, capable of nursing fertilized eggs until their hatch into impressively large crawl-away juveniles.  But within the family, their anatomy is as boringly uniform as the pleurocerids.  You crack a Viviparus shell, or a Lioplax shell, or a Campeloma shell, and look inside, and it’s basically viviparid guts.  Every time.

[22] “Retained” might be a better verb here.  The worldwide family Viviparidae seems to be ancient.  They share their peculiar concentric operculum with the Ampullaridae, which suggests that the two families are sisters.  But the viviparids have absolutely no living marine antecedents.  I take this as evidence of an hypothesis I advanced back in 2009, that evolution is slower in fresh waters than in the marine environments from which all life originated.  Like the pleurocerids, the viviparids are “living fossils.”  For more, see:

• The snails the dinosaurs saw [16Mar09]

[23] Mattox, N.T. (1937) Oogenesis of Campeloma rufum, a partheogenetic snail.  Zeitschrift fur Zellforschung und Mikroskopische Anatomie 27: 455 – 464.

Mattox, N.T. (1938)  Morphology of Campeloma rufum, a parthenogenetic snail.  Journal of Morphology 62: 243-261.

[24] Mattox sampled his study population from a tributary of the Wabash River in eastern Illinois.  Clench [10] subsequently synonymized Campeloma rufum under C. crassulum (Raf.) 

[25] Abbreviations from Vail [19] figures 5 and 10: AG = albumin gland, CM = columellar muscle, DG = digestive gland, M = mantle, O = ovary, OD = oviduct, PMC = posterior end mantle cavity, PO = pallial oviduct, PR = prostate gland, RT = right tentacle, SR = seminal receptacle, SV = seminal vesicle, T = testis, V = vagina, VD = vas deferens,  VD’ = pallial vas deferens.

[26] Vail, V.A. (1979) Campeloma parthenum (Gastropoda: Viviparidae), a new species from north Florida.  Malac. Rev. 12:85-86. 

[27]  Isn’t it interesting the way we can remember small vignettes from 40 years ago, but cannot remember what we had for supper last night [28]?  Virginia Vail gave her talk in the freshwater session of the Corpus Christie AMU meeting at 11:00 Thursday morning, August 9, 1979.  Young Rob Dillon, then listed as a graduate student at the University of Pennsylvania, gave his talk at 11:15, “The Goniobasis of southern Virginia and northwestern North Carolina: Electrophoretic and shell morphological relationships [29].”  At approximately 11:31, Old Joe Morrison jumped up and lectured me with great passion about obscure details of pleurocerid taxonomy and systematics.  At about 11:35, I said, “Easy, big fella.”  For more, see:

• Joe Morrison and The Great Pleurocera controversy [10Nov10]

[28] It was a chicken casserole, with cashews sprinkled on top.  I just looked in the refrigerator.

[29] That was just the second presentation I had ever made at a national meeting.  The research was ultimately published as: Dillon, R.T., Jr and G.M. Davis (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia 20: 83-98. [PDF]

[30] Thompson, F.G. (2000)  An identification manual for the freshwater snails of Florida.  Walkerana 10(23): 1 -96.  Also available online [html].

[31] No, it was not at an AMU meeting.  Jack Burch was never a member of the AMU/AMS during his entire professional career, as far as I know, until being elected an honorary life member in 2009.  His election was not unanimous.

[32] Clarke, A.H. (1973) The freshwater mollusks of the Canadian Interior Basin.  Malacologia 13: 1 – 509.

[33] The nomina brevispirum (Baker 1928), exilis (Anthony 1860), and gibba (Currier 1867) were not actually forgotten.  If you look forward into Burch’s “Species List, Ranges, and Illustrations” on page 92, you will find them synonymized under Campeloma decisum.

[34] “Huntsville or Stevenson, Alabama.”  This was corrected to Decatur, AL by: Clench, W. J. and R.D. Turner (1955) The North American genus Lioplax in the Family Viviparidae.  Occasional Papers on Mollusks, Museum of Comparative Zoology, Harvard. 2(19): 1 -  20. 

A Gene Tree for the Worldwide Viviparidae

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  A gene tree for the worldwide Viviparidae.  Pp 75 – 84 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

I may be mellowing in my old age.  I’m not sure.  Isaac Lea and his 505 species of pleurocerids used to infuriate me, as opposed to merely driving me nuts [1].  Frank Collins Baker's 30 species and subspecies of fossarine lymnaeids were a source of tremendous frustration to most of my 40-year career, now they are but a mild irritant [2].  I have come to understand that we scientists, no different from everybody else, can only operate by the standards of our day.  Isaac Lea’s science was good by the standards of 1862, and Baker’s great by the standards of 1911.  I’m trying to give everybody the same breaks I hope I myself will be granted 100 years from now.

So I used to find gene trees very nearly intolerable.  They started popping up in the peer-reviewed literature of the 1990s, and forests of them were disgorged from the printers of earnest graduate students in the 2000s and straight into some of the best journals publishing at that time, each pocked and wilted by some or all of the same seven cankers, which I will enumerate below, on my to overlooking at least some of the rot:

(1) The typical gene tree is typological.  During the first 10 – 15 years of the fad, the community of molecular phylogenetics rarely demonstrated any appreciation of intrapopulation or interpopulation genetic variance whatsoever.  The authors of gene trees all seemed to follow what I have described as the U1S2NMT3 rule [3], with usually one, sometimes two, never more than three individuals per population, and usually one, sometimes two, never more than three populations per species, and so forth.  At these tiny sample sizes, the significance of any sequence variation that may be brought to light cannot be assessed. 

Figure S7 of Stelbrink et al. [7]

(2) By the mid-2000s, however, sample sizes were occasionally N > 3.  At that point it became clear that intrapopulation sequence variation could surpass interspecific variation, at least in the mtDNA of freshwater and terrestrial gastropods [4].  The authors of U1S2NMT3 gene trees could not accommodate this important finding and so ignored it.

(3) Typical gene trees are rarely standardized.  Their authors often demonstrate no appreciation for original descriptions or type localities, identifying the U1S2NMT3 snails they select for sequencing by unspecified criteria.

(4) Computational phylogenetics is a nightmare fifty-years running, from which evolutionary science cannot seem to wake.  Dozens of methods have been proposed to germinate and fertilize gene trees, each with a unique set of assumptions, through which the phylogenetics community, riven by fad and fashion, cycles endlessly.  Even unto this day, the authors of gene trees typically run multiple data analyses, and publish multiple trees, from which they select their favorite.

(5) Gene trees are not species trees, or population trees, for that matter [5].  The phenomenon of incomplete lineage sorting guarantees that some fraction of the gene trees produced for any set of populations will yield a misleading picture of their evolutionary relationship, and indeed coalescence theory can be used to predict what fraction of gene trees will be flat wrong, and the molecular phylogenetics community has no way to deal with this problem, so they have doubled-down on it.

(6) Finding themselves unable to accommodate reproductive isolation in their evolutionary models, the phylogenetic community has redefined the word “species” away from a rigorously-scientific biological concept to something (anything!) their technique can actually measure.  By 2007, the USNM cladist Kevin De Queiroz was listing five species concepts, either appropriated by molecular phylogeneticists or ginned up afresh, all of which depended on arbitrary judgement calls about the significance of branch lengths and clumps [6].

(7) And then they argued that the usually-one, sometimes-two, and never-more-than-three random snails they plucked out of random creeks and identified arbitrarily constituted endangered species by criteria only they themselves could judge and wrote grant proposals to natural resource agencies to find more such precious jewel boxes of biodiversity and got them funded.  And repeat.

By the mid-2000s, the technology had reached the point that grad students were sequencing 40 -50 individual snails per dissertation, from which they were generating 40 – 50 gene trees under 40-50 different analytical assumptions, picking the result most likely to lead to additional funding.  I would sit in darkened seminar rooms for hours, watching gigantic gene trees labelled with tiny fonts, branches lit up in T-Mobile fuchsia and Mountain Dew green, and I would get such a headache.  Molecular phylogenetics is the rap music of evolutionary science, I thought – a tragic fad, a quick and easy path to job security in academia, surely it will go away.  But it hasn’t.  Neither has.

But in the last 5-10 years I have come to understand that the community of molecular phylogenetics looks at our science from a different perspective.  I look up and cannot imagine how one would begin to construct an evolutionary model of higher taxa until one had a strong model of the evolution of populations and species.  They look down and think of species and populations as following from higher taxa.  I want to make the gene tree the last chapter of my dissertation, they want to make it the first of theirs.  I think of gene trees as dependent variables, they think of them as independent variables.

From Fig. 2 of Stelbrink et al. [7]

And sample sizes have improved, as sequencing technology has advanced.  I do think I see more standardization by type locality, more calibration by intra- and interpopulation variance, methodologies to identify “bar-coding gaps,” and so forth.  At least some fraction of the molecular phylogenetics community now seem to offer their gene trees as weak, null models of population relationship, not as dowsing rods to wellsprings of imperiled biodiversity or guideposts to the promised land of rank-free classification systems.  And as that they are useful.   I guess I’ve become more forgiving.

So early last year a U1S2NMT3 gene tree of the old school crossed my desk, and it did not infuriate me nearly as much as it would have ten years ago [7].  The sequence data analyzed came from a sample of viviparids worldwide in scope, which is always commendable, collected by 16 authors from 11 different countries.  And I guess I can forgive its young first author, Björn Stelbrink (who lists both German and Swiss addresses) for ignoring intraspecific variance, given 61 nominal species in 24 nominal genera over five continents.  Doggone tree is big enough.  T-Mobile fuchsia would have been next [8].

Stelbrink and his colleagues sequenced three genes, mitochondrial CO1 and nuclear 28S and H3, for 193 individual snails.  And depicted above is the bottom half of their “BEAST-MCC” tree [9] from concatenated sequences, with “Bellamyinae – clade B” trimmed off.  The branches I have deleted – 40 tips assigned to 13 genera, are entirely Asian and African, and do not concern us in North America.

And here is the first thing to notice.  The two big oriental species widely introduced in the USA, labelled Cipangopaludina chinensis and Cipangopaludina japonica above, did not cluster with Bellamya (ss) in that mixed Asian/African "Bellamyinae - clade B" I trimmed off the top.  They clustered in the (entirely Asian) “Bellamyinae – clade A.”

Cipangopaludina was proposed by Harold Hannibal in 1912 as a subgenus of Pilsbry’s (1901) Idiopoma for Reeve’s (1863) Paludina malleata of Japan [10].  Hannibal was working from California populations of what we would today call C. japonica [11].  Clench and Fuller (1965) considered Idiopoma a simple synonym of Viviparus, continuing to accord Cipangopaludina subspecific rank [12].  Gary Pace [13] was the first to elevate Cipangopaludina to the full genus level, working with the native fauna of Taiwan.  When Burch [14] followed Pace, the rank of Hannibal’s Cipangopaludina was firmly fixed at the genus level.  And our two introduced species entered the canon as Cipangopaludina japonica and Cipangopaludina chinensis.

Those two species were universally assigned to the genus Cipangopaludina from around 1980 until 2000, when Doug Smith [15] pointed out that the characters by which Hannibal had described his genus were weak and variable, and that the rest of the world, including most workers in the countries from whence our two large viviparids must have been exported, were referring them to the genus Bellamya.

The Frenchman Félix Pierre Jousseaume proposed the genus Bellamya in 1886 to hold his typical B. bellamya, a large viviparid sent to him from Senegal [16].  Stelbrink and colleagues did not sample Jousseaume’s typical species (darn it), but they did include on their tree 15 other Bellamya samples from around Africa, and all of them clustered tightly in Clade B.

Cipangopaludina, again [17]

So the gene tree reproduced above now convinces me that our introduced species are best allocated back to Cipangopaludina, as they were classified from 1980 – 2000, rather than to Bellamya (ss), a genus name that probably ought to be reserved for African taxa.  It bothers me, a little bit [18], that Hannibal never visited Japan, proposing Cipangopaludina from America with no reference to any other viviparid taxa that might inhabit the waters of their native East Asia.  But subjectively, looking at the Stelbrink gene tree, I do see the appeal of separating Bellamyinae Clade A and Clade B as different genera.  And of the eight genus names applied to Clade A (Torotaia, Angulyagra, Sinotaia, Anularya, Celetaia, Margarya, Heterogen and Cipangopaludina), Hannibal’s Cipangopaludina is second-oldest [19].  And certainly, the first-most familiar here in America.

One other little feature of Stelbrink’s gene tree we might notice, before closing this month’s essay.  Viviparus georgianus was described by Isaac Lea from Hopeton, Georgia in 1834, and up until the 20th century was unknown in waters further north.  Clench [20] dated its arrival in the northeastern United States to Boston in 1916, from whence it has spread widely, across New England and New York through Michigan, Illinois and Wisconsin, even into southern Canada. 

Arthur Clarke [21] noted the striking similarity between Canadian populations of V. georgianus and the European Viviparus viviparus, speculating that Canadian Viviparus populations might represent a cryptic invasion from Europe.  The sequence data do not bear this hypothesis out, however.  The gene tree above depicts three European species, V. viviparus, V. ater, and V. contectus, as strikingly divergent from the North American V. georgianus, V. subpurpureus, and Tulotoma magnifica.  The Stelbrink results do not directly address Clarke’s cryptic invasion hypothesis, as the individual V. georgianus Stelbrink sequenced seems to have been collected from Alabama [22].  But GenBank also holds several CO1 sequences from V. georgianus populations sampled in Canada and New York, and all those demonstrate 98-99% matches to Stelbrink’s Alabama sequence, roughly 85% similar to the nearest European Viviparus.

So gene trees, even old-school U1S2NMT3 specimens such as we have reviewed in the present blog post, can offer some insight into coarse genetic relationships among far-flung taxa.  But how about more interesting and important questions?  Stelbrink and his colleagues also seem to have included six nominal species of Campeloma in their analysis, one snail each, in that orange block near the bottom of their tree.  Can their cute little data set tell us anything about population relationships among the North American Campeloma?  Tune in next time.

Notes

[1] This is a reference back to my series of essays on Pleurocera troostiana:

• Isaac Lea Drives Me Nuts [5Nov19]

[2] We’re going to have much more to say about the crappy little amphibious lymnaeids often referred to as “fossarines” in coming months.  But for now, see:

• The Legacy of Frank Collins Baker [20Nov06]
• The Classification of The Lymnaeidae [28Dec06]
• The Lymnaeidae 2012: Fossarine Football [7Aug12]

[3] For coinage of the “U1S2NMT3 Rule,” see:

• The Lymnaeidae 2012: Stagnalis yardstick [4June12]

[4] For all you could ever want to know about intrapopulation mtDNA sequence divergence, see:

• Mitochondrial Superheterogeneity: what we know [15Mar16]
• Mitochondrial Superheterogeneity: What it means [6Apr16]
• Mitochondrial Superheterogeneity and Speciation [3May16]
• Mitochondrial heterogeneity in Marstonia lustrica [3Aug20]

[5] For more about gene trees and reproductive isolation, see:

• Gene Trees and Species Trees [15July08]
• What is a Species Tree? [12July11]

[6] Five of the 11 species concepts listed in de Queiroz Table 1: Evolutionary, Phylogenetic (Hennigian), Phylogenetic (Monophyletic), Phylogenetic (Genealogical), and Phylogenetic (Diagnosable).  See: De Queiroz, K. (2007)  Species concepts and species delimitation.  Syst. Biol. 56: 879 – 886.

[7] Stelbrink, B., R. Richter, F. Köhler, F. Riedel, E. Strong, B. Van Bocxlaer, C. Albrecht, T. Hauffe, T. Page, D. Aldridge, A. Bogan, L-N. Du, M. Manuel-Santos, R. Marwoto, A Shirokaya, and T. Von Rintelen (2020)  Global diversification dynamics since the Jurassic: Low dispersal and habitat-dependent evolution explain hotspots of diversity and shell disparity in river snails (Viviparidae).  Systematic Biology 69: 944 – 961.

[8] In fact, both Stelbrink’s Figure 3 (unconstrained versus fossil-constrained tree) and his Figure 4 (Ancestral state estimation tree) did go T-Mobile-Fuchsia on us, plus Mountain-Dew-Green and a Change-of-Life-Blue that reminded me of a pants suit my wife bought at a yard sale in 1997.  Ouch.

[9] The most recent cycle of fad and fashion in computational phylogenetics seems to have brought to the top a cross-platform program called “BEAST,” Bayesian Evolutionary Analysis Sampling Trees.  The Stelbrink tree was generated using the “MCC” algorithm, Maximum Clade Credibility.  Oh good, that’s what's wanted around here.  Maximum credulity.

[10] Hannibal, H. (1912)  A synopsis of the Recent and Tertiary land and fresh water Mollusca of the Californian Province, based on an ontogenetic classification.  Proceedings of the Malacological Society of London 10: 112 – 211.

[11] Large, exotic viviparids, initially identified as Paludina japonica, were first recorded in San Francisco fish markets around 1892.  The first record of a naturalized population seems to be Stern’s 1901 report from the San José area.  For more, see:  Hannibal H. (1911) Further notes on Asiatic Viviparas in California.  Nautilus 25: 31 – 32.

[12] Clench, W.J. & S.L.H. Fuller (1965) The genus Viviparus (Viviparidae) in North America. Occ. Pap. Moll., 2(32): 385-412.

[13] Pace, G. L. (1973) Freshwater Snails of Taiwan (Formosa).  Malacological Review Supplement 1: 1 – 118.

[14] 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).

[15] Smith, D.G. (2000) Notes on the taxonomy of introduced Bellamya (Gastropoda: Viviparidae) species in northeastern North America. Nautilus 114: 31-37.

[16] Jousseaume, F. (1886) Coquilles du Haut-Senegal.  Bulletin de la Societe Zoologique de France 11: 471 – 502.

[17] The photo above of the impressive Cipangopaludina japonica die-off was snapped 12Jan21 by Mr. Brandon Jones, the Catawba Riverkeeper, on the muddy shore of the Fishing Creek Dam tailrace, at Great Falls, SC.  This point is about 30 km upstream from the Wateree Dam, which I described as:

• Just Before The Bust [5Aug14]

[18] It shouldn’t.  Remote description of distant biotas has been standard operating procedure in systematic biology for 200 years.  The Europeans got all our pretty seashells, darn them.

[19] Actually, Margarya was described by Neville in 1877.  If I were a Pharisee, I would demand that our two big viviparid guests here in North America be identified as Margarya japonica and Margarya chinensis.  But let’s see how opinion evolves in The Orient.  I suppose it is possible that some actual biology might come into play here, as well.

[20] Clench, W.J. (1962) A catalogue of the Viviparidae of North America with notes on the distribution of Viviparus georgianus Lea. Occ. Pap. Moll., 2(27): 261-287.

[21] Clarke, A.  (1981)  The Freshwater Molluscs of Canada.  National Museums of Canada.  445 pp

[22] I am not entirely sure on Stelbrink’s V. georgianus locality.  There seems to be an error on that line in his Supplementary Table S1.

Snails by Mail

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Snails by Mail.  Pp 45 – 49 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Last month we surveyed the elements of the freshwater gastropod fauna widely available to hobbyists in the Big Box retail outlets that seem so dominant on the landscape of aquarium supply today [1].  We found two categories of snails reliably offered for sale, strikingly different in their biology but ironically similar in their provenance – the “mystery snails” (Pomacea bridgesii/diffusa) and the nerites.  But, as my readership has already doubtless inferred from my essay of 9Oct17 [2], ampullariids and neritids do not the entire market comprise.  What else might be available online?

Assassin Snail - Aquatic Arts

If one simply enters “freshwater snails” on the subject line of a google search, the first 50 hits include four major retail suppliers – Amazon, eBay, aquaticarts.com, and liveaquaria.com.  Most of the stock available for purchase from these sources are (once again) nerites or mystery snails in their various color varieties.  But below I have compiled a brief review of the remainder, sorted into seven pigeonholes.  The first four taxa or groups of taxa appear to be widely available for purchase online, the next two categories seem to be occasionally available, and the last category is what I would call a “wastebasket.”

Ramshorns – These easy-to-culture snails seem to have remained a perennial favorite of aquarium hobbyists for many years, at least since I was a kid.  All the stocks with which I had any personal experience growing up were North American Helisoma trivolvis, but today it is my impression that most "ramshorns" are Floridian Helisoma scalaris duryi [3].  Ng and colleagues [4] identified Singapore ramshorns as Oriental Indoplanorbis exustus, on the other hand, and I've even seen European Planorbarius corneus implicated in what seems to be a global planorbid conspiracy.  What the heck are these snails?  Most of the offerings for sale online today are “red ramshorns,” which are actually albinos, their absence of body pigmentation allowing that red hemoglobin so characteristic of planorbids to show through.  Stocks with wild pigmentation are marketed as either “brown” or “black.”  There is also a “leopard” variant for sale that has patchy pigmentation on its mantle, and a “blue” that (I think) demonstrates some sort of mutation in shell pigmentation.  I wish I knew more about that, too.

Assassin Snails – Approximately thirty nominal species of the nassariid genus Clea (or Anentome) burrow in the soft bottoms of broad, coastal rivers from southern China and Southeast Asia into The Philippines.  What fascinating creatures!  The group is one of only two neogastropod genera to have successfully invaded fresh waters [5].  As their name implies, assassin snails are predatory – hunting other freshwater snails and sucking them out of their shells.  The little tigers widely marketed to the aquarium hobby today are universally identified as Clea helena, but the excellent recent study by Ellen Strong and colleagues [6] suggests that commercial stocks may represent as many as four species, none of which seems to match topotypic Anentome helena from Java.

Rabbit Snails – Several species of the pachychilid genus Tylomelania are not uncommonly offered for purchase online, variously marketed as “giant” or “orange” or “golden” rabbit snails.  It may be recalled from my October essay that Ng and colleagues [4] identified four Tylomelania species in the Singapore aquarium trade, all of which are apparently endemic to Lake Pozo on the Indonesian Island of Sulawesi.  Some conservation concern has been expressed, but see the follow-up essay I published on this subject in November [7].

Japanese Trapdoor Snails – Yes, our old familiar Bellamya japonica (or maybe B. chinensis?) often seems to be marketed to the indoor aquarium hobby, generally labelled as "Viviparus malleattus.”  The biology of these large oriental viviparids will be well known to my FWGNA readership, but see my species pages [japonica] and [chinensis] for a refresher.

Rabbit Snail - Aquatic Arts

Pagoda Snails – Several nominal species of the pachychilid genus Brotia bearing heavy, strikingly spiny or tuberculate shells are harvested from the rivers of Thailand and occasionally available from online retailers as “Pagoda snails.”  We touched on these back in October as well.

Chopsticks, Spikes, or Long nosed Snails – Occasionally the discriminating freshwater gastropod connoisseur will find thiarids of the genus Stenomelania offered for sale online.  Again, Ng and colleagues [4] identified four Stenomelania species marketed in the Singapore pet trade, although raising no conservation concerns.  The Discover Life website lists 36 nominal species in the genus, ranging throughout Southeast Asia, Australia, and Oceania.  The most common specific nomina mentioned in the pet trade are Stenomelania torulosa and S. plicaria, both distributed widely from India through Indonesia to China.

The Wastebasket – Although (almost) universally reviled, stocks of the “Malaysian Trumpet Snail” (Melanoides tuberculata) are available for purchase on Amazon and eBay.  This invasive thiarid, apparently native to low latitudes throughout the Old World (in various clones), has been widely introduced into the New.  See my FWGNA species page [tuberculata] for more.  And (if you can believe it) hobbyists with a thirst for the small, brown, and mundane can also purchase Physa acuta stocks from Amazon.  I get the impression that both the Physa and the Melanoides are primarily marketed as prey for Assassin snails.  The Physa listing on Amazon advertises, “great natural food for your puffer.”

What I did not find for sale online last week, thank heaven, was any ampullariid stock other than Pomacea bridgesii/diffusa. I remember in years past being able to purchase, at least occasionally through mail order or mom-and-pop aquarium stores, Pomacea insularum/maculata (“Golden Apple Snails”), Pomacea paludosa (“Florida Apple Snails”) and Marisa cornuarietis (“Giant Ramshorns.”)  But I was unable to find, at least upon superficial search, any listing for any such invasive ampullariids through the major online retail outlets today.

So to conclude.  Should we be concerned that any of the freshwater gastropod groups listed above might escape to become pests here in North America, other than the ones already introduced and spreading?  We have reviewed the criteria for invasiveness on quite a few occasions in the past [7], ultimately settling on two ecological qualities which I have called “weedy” and “different.”  So the ramshorns, trapdoors, and wastebaskets are already here.  And the rabbits, pagodas, and chopsticks are not all that ecologically different from North American pleurocerids, in many cases, nor do their life histories seem especially weedy.  That leaves the Assassin snails.

Could an introduction of Clea succeed here in North America?  Some concern has already been expressed [8].  All the range maps I have seen for the genus seem to suggest that their natural distribution is entirely tropical – apparently ranging from the equator to around 20 degrees N latitude.  So our own Key West floats in the Caribbean at latitude 24.5 degrees N, perhaps still a bit too temperate to raise concerns about the threat of gastropod assassination here in the USA.  But you all down in Mexico and Central America might best be on the lookout.

Notes

[1] Pet Shop Malacology [21Dec17]

[2] What’s Out There?  [9Oct17]

[3] Subsequent to the publication of this essay I posted a lengthy series on Helisoma scalaris duryi, starting in October of 2020 and going onward for at least five or six months.  I do suggest that you skip ahead here and read forward into 2021 if you are genuinely interested in "ramshorns":

• The flat-topped Helisoma of The Everglades [5Oct20]

[4] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130. https://doi.org/10.1371/journal.pone.0161130

[5] The only other neogastropod group to invade fresh waters is the marginellid genus Rivomarginella.

[6] Strong EE, Galindo LA, Kantor YI. (2017) Quid est Clea helena? Evidence for a previously unrecognized radiation of assassin snails (Gastropoda: Buccinoidea: Nassariidae) PeerJ 5:e3638 https://doi.org/10.7717/peerj.3638

[7] Loved to Death?  [6Nov17]

[8] For the biology of freshwater gastropod invasions, see:

• Invaders Great and Small [19Sept08]
• Community Consequences of Bellamya Invasion [18Dec09]
• The Most Improbable Invasion [11Oct12]
• The Many Invasions of Hilton Head [16Dec15] 

[9] Mienis HK. 2011. Will the uncontrolled sale of the snail-eating gastropod Anentome helena in aquarium shops in Israel result in another disaster for Israel’s native freshwater mollusc fauna? Ellipsaria 13(3):10-11.  Bogan AE, Hanneman EH. 2013. A carnivorous aquatic gastropod in the pet trade in North America: the next threat to freshwater gastropods. Ellipsaria 15(2):18-19