Dr. Rob Dillon, Coordinator





Tuesday, February 9, 2021

The Emperor, the Non-child, and the Not-short Duct

In last month’s post [5Jan21] I conducted you, my loyal and long-suffering readership, through the long and agonizing process by which I was personally able to distinguish the Floridian Helisoma duryi from the broadly-North-American Helisoma trivolvis.  The characters that ultimately did the trick for me, after years of abject confusion, were entirely shell morphological.

Nobody has subsequently asked me any of the natural follow-up questions, but I’ll bet a lot of you thought them.  Might there also be some sort of anatomical difference between H. duryi and H. trivolvis?  Did I ever dissect any of those snails?

The quick answers are “maybe” and “Fuhgeddaboudit.”  The rationale behind those answers, however, is far from quick.  So if you’re thirsty for another deep dive into the obscure history of another obscure malacological topic, full of obscure characters summoned from their graves to further muddy the already murky waters, read on.  Otherwise, I’ll see you next month.

Frank Collins Baker is a hero of mine.  That was the opening sentence of my blog post way back in [20Nov06], subsequently becoming the opening sentence in Volume 2, Essays on the Pulmonates published by the FWGNA Project in 2019 [1].  I’ve said it three times now.  I’m serious, I mean it.

Baker's 1902 Helisoma trivolvis [2]

Baker’s work was not modern.  He died in 1942, the year Ernst Mayr proposed the biological species concept.  But I would hold Baker’s work up as the zenith, the pinnacle, the very paragon of late pre-modern systematic malacology.  And as exhibit A, I would direct the jury to Baker’s treatment of one of the most common, widespread, familiar gastropods of North America fresh waters, Helisoma trivolvis.

Baker published his first study of Helisoma trivolvis in the second volume of his groundbreaking “Mollusca of the Chicago Area” [2].  As of 1902, he was still considering Planorbinae a subfamily of the Family Lymnaeidae.  So, after devoting a page of description to the genus Planorbis of Guettard 1756, and a brief treatment of the subgenus Helisoma of Swainson 1840, Baker devoted three pages to Planorbis (Helisoma) trivolvis (Say 1817), including 11 references, an original drawing of the radula and a 12 x 4 table of shell measurements.  And in his plate xxxii, he treated us to 15 photographic shell images, including a growth series.

Baker returned to the subject of Helisoma trivolvis in Part 1 of his landmark “Freshwater Mollusca of Wisconsin” [3].  By 1928 he was considering the Planorbidae a separate family, to which he devoted five pages of description, using H. trivolvis as exemplar for the family, drawing the external morphology of the animal and its stomach.  Then to the genus Helisoma he devoted nearly six additional pages of description, with drawings of a living adult crawling, a living juvenile crawling, the jaw morphology, and a lovely, detailed figure of the H. trivolvis reproductive system, including genitalia.

As of 1928, Baker had transferred H. trivolvis to the subgenus Pierosoma of Dall (1905), to which he devoted another page of description, with the figure of the penial morphology reproduced below.  The blue circle is the penial gland (internal in this view), the red circle is the bump on the exterior [4] of the penis corresponding to where that penial gland is sitting, and the arrow shows the duct leading from the penial gland to the sac around the penis.  Then (finally!) we arrive at the description of Helisoma (Pierosoma) trivolvis, the typical subspecies, which warrants another four pages of text, 14 references, a 9 x 4 table of shell measurements, a radula figure, and 15 shell figures on Baker’s Plate xx.

I will simply mention, in passing, that Baker recognized two subspecies of Helisoma trivolvis other than the typical, including H. trivolvis pilsbryi (Baker 1926), to which he devoted an additional four pages.  And an additional eight pages to three other species in the subgenus Pierosoma, including truncata (Miles 1861), all of which we now understand to be junior synonyms of H. trivolvis.  There is no evolutionarily-significant difference between the two penial complexes Baker drafted below – just accidents of preservation.  By now, you must get the picture.

And I will also remind my readership at this point that Baker was not done with the Planorbidae.  Both his 1902 work and his 1928 work were printed in octavo.  His worldwide “Molluscan Family Planorbidae,” published posthumously in 1945, was a quarto volume of 530 pages [5].

From Baker [3] Circles = penial gland, Arrow = Not short duct

Alas, my hero passed away on May 7, 1942, leaving his planorbid monograph unfinished.  He did, however, write a draft of his preface in January of that year.  And here is the topic sentence of preface paragraph two:

“Unlike the terrestrial pulmonates (Stylommatophora Pulmonata) which have been brought to a high state of precise classification from the anatomical studies of Dr. Henry A. Pilsbry and his co-workers, the Basommatophora are still in a condition of more or less chaos as regards classification, all of the monographs and many of the local studies being based wholly or partly on characteristics of the shell…”

. . . and so forth.  The hero of my hero was Dr. Henry A. Pilsbry.  Pilsbry was Baker’s mentor 1889 - 1890 and wielded immense influence over North American malacology for 70 years.  So, in December [3Dec20] we opened the cover of Pilsbry’s 1934 contribution to the biology of the Planorbidae, focused on Florida but aspiring to worldwide scope [6].  We are now in a position to evaluate Pilsbry’s paper in its historical context – after Baker 1902, after Baker 1928, and before Baker 1945.  How did His Imperial Majesty’s 1934 contribution compare to that of the colleague who idolized him?

Pilsbry’s introductory material is almost entirely acknowledgement, in which he lists a variety of curators, colleagues and correspondents from all over the USA, neglecting Baker.  Then he heads his second page with “Helisoma, Subgenus Pierosoma Dall,” subheads “Helisoma trivolvis intertextum (Sowb),” and lists four references.  These are to Planorbis glabratus Say of Binney (1865), which Pilsbry hastens to stipulate are “not the description; not of Say,” Planorbis intertextus of Sowerby (1878), Planorbis tumidus Pfr of Simpson (1887) which Pilsbry hastens to stipulate is “Not of Pfeiffer,” and “?Planorbis glabratus var. reticulatus Dall” of Bartsch (1916), which Pilsbry notes was “name only.”

Pilsbry then just launches in, assuming that we, his readership, are already familiar with planorbid anatomy.  More even than broad-brush planorbid anatomy, Pilsbry assumes that we are familiar with the detailed anatomy and shell morphology of typical Helisoma trivolvis trivolvis.  So this is how his description begins:

“The southeastern form of the Austroriparian H. (Pierosoma) trivolvis lentum (Say) is distinguished by its smaller size and flatter form.  The inner whorls of the shallowly concave left side are flattened and have an acute keel, normally concealed in the suture, the last whorl normally becoming rounded on that side.  The right side…”

… and so forth.  Pilsbry seems to have measured but a single shell of H. trivolvis lentum, for which he reports, “Diam. 17, alt. 5.5 mm; 5 ½ whorls.”  What, precisely, is this shell smaller and flatter than?  Smaller and flatter than the 12 x 4 table of shell measurements that his disciple F. C. Baker published from the Chicago area H. trivolvis in 1902?  Smaller and flatter than the 9 x 4 table of shell measurements Baker published from Wisconsin H. trivolvis in 1928?  Why didn’t Pilsbry cite any of the work of F. C. Baker?

Not only is Baker’s name entirely absent from Pilsbry’s review of H. trivolvis [7], none of the 14 H. trivolvis references that Baker listed in 1928 were passed along by Pilsbry, including Say’s original description of 1817.  All we were given for comparison is the intertextus of Sowerby, the not-description of glabratus published by Binney, the tumidus not of Pfeiffer, and the name-only reference to glabratus in Bartsch.  Pilsbry admits no antecedents.  Angels have led him to a stone box buried in upstate New York and stood over his shoulder as he has transcribed his description of Helisoma trivolvis lentum from golden plates he has discovered therein.

This is more than an unprofessional slight.  Pilsbry’s cavalier disregard of prior research has scientific consequences for us who labor in his footsteps today.  The main point of the first section of Pilsbry’s 1934 work was not to review Helisoma (Pierosoma) trivolvis, but to describe a new subgenus, Seminolina, into which he would segregate four Floridian species, including H. duryi.  What if some future worker, hypothetically of course, wanted to distinguish H. duryi, or indeed any of those Floridian Helisoma, from H. trivolvis?

Pilsbry described the shell only of H. trivolvis lentum; he apparently had no fresh or preserved material before him.  Nevertheless, on page 2 of his paper he jumped abruptly into the description of his new subgenus.  And here is Pilsbry’s definition of Seminolina, quoted in its entirety:

Helisomas in which the external duct from penial gland to upper sac is short and adnate. Shell shaped like Pierosoma or with the spire produced on the left side and scalar, Physa-shaped. The smooth or malleate surface is not thread-striate, usually glossy. Type Helisoma scalare (Jay).”

The ”shell-shaped-like-Pierosoma” character does not help us at all, and we beat that “not-thread-striate” shell character to death last month [5Jan21].  That leaves us with Pilsbry’s “duct-short-and-adnate” character.  Again, I ask.  Compared to what?

From Pilsbry [8]. Circles = penial gland, Arrows = "short" duct.

Before we go any further, I must emphasize that I am not criticizing Pilsbry for his subjectivity.  Subjective description was the standard of practice in pre-modern systematic biology, and the entire worldwide malacological community wrote stuff like “animal very dark olivaceous” or “duct short” or “penis ample,” including both F. C. Baker and H. A. Pilsbry, and I am not complaining about that.  Far be it from me to judge our esteemed forefathers by modern standards, like some common Democrat.

But I do not think it unreasonable, by 1934 standards, to expect Pilsbry to try to communicate to his posterity, ideally to show us, the difference between a duct that is short and adnate and a duct that is not short and not adnate, especially when he is erecting a higher-level taxon on the basis of that character.

So Pilsbry did offer us one lovely montage illustrating various aspects of the anatomy of his subgenus Seminolina, featuring H. scalare and three subspecies of H. duryi, as reproduced above.  He only labelled the penial gland on one of the ten figures he drafted of the Seminolina penis, but in fact that organ is illustrated six different times, in four different animals, as encircled directly on the figure above.  In almost all these figures, the penis is opened to expose the penial gland, circled in blue.  In four cases, circled in red, the penis has not been opened, so that the penial gland appears as a bump.

He never labelled the “external duct from penial gland to upper sac,” the key character by which the subgenus Seminolina is to be distinguished from the subgenus Pierosoma, in any of his figures.  It is best visible in figures B and J, where I have placed the red arrows, and sort-of visible, obscured by the penis, in figures C and K.  That is the organ which Pilsbry described as “short and adnate.”

So for a third time I ask, compared to what?  Insofar as I am aware, only one figure of the penial gland of Helisoma trivolvis had been published as of 1934, but it was a good one.  The penial gland is encircled in red in that figure from Baker 1928 I have reproduced way up above.  And the “external duct from penial gland to upper sac” of H. trivolvis which, to be precise, is not short and not adnate, is marked with a red arrow.

Baker’s 1928 figure was drafted at a larger scale than Pilsbry’s, it was offered in cross section, and it was semi-diagrammatic.  It cannot be compared to the figures Pilsbry has offered us in 1934 to support the distinction he has drawn between Pierosoma and Seminolina.  In two words, Pilsbry was artistic, Baker was scientific.  How are we, who follow in these great men’s footsteps, to distinguish the short from the not-short?

By the blessings of Divine Providence, however, F. C. Baker was, even at the time Pilsbry published his 1934 paper, working on his 1945 monograph [9].  Here he would compare duryi and trivolvis side-by-side, in some standard fashion.

In the figure below I have patched the top half of Baker’s Plate 24, showing the penial morphology of Helisoma trivolvis, together with the top half of his Plate 33, showing Helisoma duryi.  And again, I have marked the external duct from penial gland to upper sac, which Baker abbreviates “DC” for duct of gland, with red arrows.

From Baker [5]. Circles = penial gland, Arrows = penial gland duct.

OK, first set aside plate 24 figure 3, which depicts a juvenile H. trivolvis.  Then other than that case, I think I do see the phenomenon that Pilsbry was talking about.  The duct from the penial gland does indeed appear longer in Baker’s three adult H. trivolvis figures than in Baker’s eight H. duryi figures.

I have a couple misgivings, however.  First, some of the variance in the duct length is due to swelling in the penial gland to which it attaches, which (for example) is very pronounced in trivolvis figure 1 and duryi figure 9, but negligible in trivolvis figure 5 and duryi figure 1.  The same phenomenon is vivid in Baker's 1928 comparison of the Helisoma trivolvis and Helisoma truncata penial complexes way up above, which we now understand to be identical.

Of much greater concern, however, is that the entire penis appears taller and skinnier in all three trivolvis than in all eight duryi, not just the duct of the gland, but everything.  And in my experience, that usually means a difference in preservation.  It seems likely to me that Baker may have dissected his trivolvis alive, but his duryi preserved [10].

Here in the modern era of systematic biology, we understand that the length of a tube or duct of unreinforced epithelium in some exemplar or set of exemplars, carefully chosen or randomly selected, is not a good character by which to construct evolutionary hypotheses about animal populations.  It is too susceptible to non-heritable variance, too difficult to measure, and too subjective to describe otherwise.

In my mind’s eye, I see my hero, F. C. Baker, rising from the lab bench where he has just completed drafting his Plate 33, turning to the glittering malacological host assembled, and exclaiming,

 “There is no evidence that variance in the length of the penial gland duct is evolutionarily significant in Helisoma, but even if such evidence were to present itself, you can’t base a subgenus-level distinction on that single ridiculous character, for Chrissake!”

But Baker was not a na├»ve child standing in the crowd as The Emperor passed.  He was a courtier, following in retinue behind.  So, in the end, Baker’s observations confirmed those of his Emperor.  Here is the lead sentences in his remarks under the subgenus Pierosoma (pg 149):

Pierosoma is a very distinct group of Helisoma, distinguished from the subgenera Helisoma and Seminolina by peculiarities of genitalia and radula.  The duct of the penial gland is always longer in adult animals than in the other groups mentioned.”

I will conclude this month’s post with yet another confession of error, my third in three months.   In the brief biography of F. C. Baker I posted on [20Nov06], I referred to my hero as “the freshwater Pilsbry.”  Over the last several months, however, I have found many opportunities to compare the work of these two giants of late-premodern American malacology side by side.  And my earlier assessment was an insult to Baker.  Henry Pilsbry couldn’t carry F. C. Baker’s malacological jock strap.

Note added in postscript.  As I wrote the essay above I tried to maintain a professional distance from the subject matter, aiming for a strictly objective and dispassionate review of previous research on certain obscure details of planorbid reproductive anatomy, failing.  In the essay that follows, posted [26Jan21], I have explored the personal relationship between Pilsbry and Baker, making no pretense of professionalism whatsoever.


Notes

[1] For a bit of biography and a quick review of his contributions, see either:

  • Dillon, R. T., Jr. (2019b)  The legacy of Frank Collins Baker.  pp 1-5 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston. [FWGNA Publications]
  • The Legacy of Frank Collins Baker [20Nov06]

[2] Baker, F.C. (1902)  The Mollusca of the Chicago Area, Part II, The Gastropoda.  The Natural History Society Bulletin 3: 131 – 410.  Chicago Academy of Sciences.

[3] Baker, F.C. (1928) Freshwater Mollusca of Wisconsin, Part I, Gastropoda. Bull. Wisc. Geol. Natur. Hist. Survey, no. 70. Madison: University of Wisconsin Press.

[4]  Actually, during copulation this entire organ is everted like you’d turn out a sock.  So whatever is internal in this image would be external during copulation, and vice versa.  All those ducts and tubes are, of course, inside the penis when it is doing its job.   But the convention (at least in the late premodern tradition) is to call things “internal” in their dissected view, such as we have here.

[5] Baker, F.C. (1945) The Molluscan Family Planorbidae. Urbana: University of Illinois Press.  530 pp.

[6] Pilsbry, H. A. (1934)  Review of the Planorbidae of Florida, with notes on other members of the family.  Proceedings of the Academy of Natural Sciences of Philadelphia 86: 29 – 66.

[7] Pilsbry only referred to Baker’s 1928 work four times, all in his second section, almost entirely to dismiss it.  In his discussion of the reproductive anatomy of Planorbula, for example, Pilsbry footnoted: “Baker's figures seem to be somewhat diagrammatic, and do not agree fully with those I prepared for the unpublished New York monograph, especially in the form of the prostate gland and various details of penial structure.”  What, exactly, doesn’t agree with observations you haven’t published?  And never will?  Jackass.

[8]  Here is the full caption of Pilsbry’s [6] Figure 1: Fig. la, teeth of Helisoma scalare; b, genitalia; c, d, the penis opened, in d the penial gland of same specimen pulled downward; e, jaw. f, g, Helisoma duryi intercalare, penis and penial gland. h-h1-h2, genitalia of Helisoma duryi normale, at h1, the penis opened. i, j. k, H. d. seminole, penes. pg, penial gland; pr, prostate gland; v, verge.

[9] In his preface of January 1942, Baker said, “The present volume on the Planorbidae was begun some twenty-five years ago and has been in active preparation for the past ten years.”  Pilsbry almost certainly knew that Baker was already hard at work on the Planorbidae in 1934.

[10]  Indeed, problems of this same sort were noted by Pilsbry.  Under H. scalaris (p 35), he wrote: “The stouter shape of the verge in H. d. seminole may be due to greater contraction, as the specimens had evidently been killed in strong alcohol.”