Lamarck was Right

The Lymnaaeidae family of freshwater snails are right-handed pond snails. Common in the water hole near you. 

Early workers on freshwater snails distinguished three genera within the Lymnaeidae family: Lymnaea, described by Lamark in 1799; Galba, described by Schrank in 1803; and Stagnicola, described by Jefferys in 1830. A wee bit later, in 1885, the genus Fossaria was described by Westerlund; this is generally accepted to be a synonym of Galba. Hubendick reined things back a bit, putting them all in the same genus, Lymnaea, in his 1951 work, indicating that the differences were so minor that separate genera were unjustified. 

Side Note: I’m ignoring more than a few genera, namely Radix, Bulimnea, Plurolinaea, and Acella. I’ll list even more later, so stay tuned. 

And there it did not stay: Workers on snails have swapped back-and-forth using these genera, or not, over the years. It gets confusing as the first designations were separated primarily by the size of snails: Lymnaea was the largest, Galba was the smallest, with Stagnicola in between. That may help distinguish them quickly and easily, but it is not biologically sound. With the advent of molecular evidence, this would all be cleared up; maybe it has helped. The molecular data has shown that many of the nominal species within this family are not so, particularly the number of tiny snails: In one case, 10 named species have been condensed into a single species. Indeed, in one recent paper by a slew of authors led by Alda and published in 2021, shows that there are only 2 species of small Lymnaeids in North America. Phew, it was hard to tell these snails apart, mainly because the differences were not apparent (or real), and many morphological differences are due to phenotypic plasticity. Also, species descriptions in the good ole days of yore sucked: As an example, let me use the description of Lymnaea bulimoides by Lea in 1841: 

Here is my translation:

Shell ovate-conical, thin, smooth, clean, transparent, dark-yellow, minute holes in them; base rather short; small sutures; whorls five subconvex; aperture oval.

That’s it.

In Baker’s 1911 work on the Lymnaieds, at least the descriptions were enhanced, and a tiny image was provided. 

Baker’s description of Galba humilis:

Small, ovate-conic; periostracum light yellowish horn; surface shining, sometimes polished; lines of growth crowded, prominent ; spiral sculpture absent or but slightly indicated; apex as in Galba humilis modicella; whorls 5-5^, convex, rather rapidly increasing in diameter, the body whorl quite obese; spire conic, turreted, about as long as the aperture; sutures well impressed; aperture ovate or roundly ovate; peristome lip thin; inner lip reflected to form a narrow, somewhat triangular expansion which may be rolled in toward the umbilical chink or stand more or less erect; umbilical chink small and narrow, emarginated by the inner lip; parietal callus well marked; axis smooth, forming a column as in Galba cubensis. 

And even though he suggested some aspects appeared like Glaba cubensis, he considered this a separate species. These species are still considered distinct.

Some molecular work by Correa and colleagues in 2010 noted (I’ll bring up this study again later):

“Our results indicate that genera in Lymnaeidae do not reflect phylogenetic relationships, to the notable exception of Radix…” 

This suggests, again, that we should not use size to assign the genus and that the number of genera is smaller than hypothesized. The Freshwater Gastropods of North America project (FWGNA) recommends using the genus Lymnaea for all members of this family except the aforementioned Radix (FWGNA.org). This seems a safe suggestion until we can work this out.

Let me back up a little. In 2002, a paper came out suggesting that a new genus—yes, you heard me—a new genus—be assigned to a few species of snail then designated under either the genus Stagnicola or Lymnaea. The new genus they proposed was Catascopia. They based their hypothesis on the vast difference in the length of a segment of DNA known as ITS-2.

Now you may be thinking, why come up with a new genus when at least 4 very used genera, Lymnaea, Stagnicola, Galba, and Fossaria, are available? The reason is the same reason old Millionaires and Billionaires give money to colleges to put up a building with their name on it; they are trying to put their mark on the world. 

This ramble does not end here; there is another big step. If you can handle it, read on.

In 2013, a snail worker (Vinarski) suggested that those snails placed in Catascopia by the 2002 paper should be placed in the genus Ladislavella because this name was designated in 1913 by B. Dybowski, and 1913 being much before 2002 would take precedence following the rules of nomenclature (yes there are rules even if they are ignored at times).

Yes, another genus. Following the 2013 “suggestion” was an effort to replace the Catascopia name, and then further leaps to usurp other snails in the genera Stagnicola, with Ladislavella. This is bogus. Let me type it out so I can get it into my head because it is daft: The worker (Vinarski) first says Ladislavella must replace Catascopia because it’s an older name (rules are rules, the older name gets precedence in science taxonomy) but then replaces Stagnicola (a much older name being designated in 1830) with Ladislavella as well.

Bogus stuff is happening here. Is B. Dybowski a relative of Vinarski, and does he want to “put his name on a building”?

Let’s look at a list, shall we:

The list below is a subset, I kid you not, of the Lymnaeidae genera proposed: When (in order) and by whom they were named. I placed a gap before the 1900s; there were 11 genera to choose from before then, at least 11 (I did not list them all).

Lymnaea: 1799 by Lamarck.

Galba: 1803 by Schrank.

Radix: 1810 by Montfort. (A unique-looking shell, wide aperture)

Omphiscola: 1819 by Rafinesque.

Stagnicola: 1830 by Jeffreys.

Acella: 1841 by Haldeman.

Bulimnea: 1841 by Haldeman.

Erinna: 1858 by H. Adams & A. Adams. (Two species from a river in Borneo).

Lanx: 1880 by Clessin.

Corvusiana: 1881 by Servain.

Fossaria: 1885 By Westerlund.

(Eleven genera up to this point)

Pseudosuccinea: 1908 by  F.C. Baker.

Pectinidens: 1911 by Pilsbry.

Fisherola: 1912 by Hannibal.

Ladislavella: 1913 by B. Dybowski.

Hinkleyia: 1928 by F.C. Baker.

Aenigmomphiscola: 1981 B. Kruglov & Starobogatov.

Walterigalba: 1985 by Kruglov & Starobogatov.

By 1985, there were at least 18 genera for species of Lymnaeids, yet Meier-Brooks decided we needed another: I know I’ve covered this ground already, but it still blows me away.

The extension to the list would be this:

Catascopia: 2002 by Meier-Brook & Bargues

Correa et al. (2010) detailed molecular analysis that proposed that nearly all of the genera above be called Lymnaea, with a few exceptions: Radix was distinct, for example. Please, please, please, let’s do that. Confusion like this is why biology students flee to other fields (I’m paraphrasing the great Lynn Margulis here).

Let me remind you that the first genus, the one that nearly all of the snails should be placed under, was described by our friend, the much-maligned in biology textbooks Lamark. It turns out he was right.

Sources and Further Readings:

Adams, A. 1855. Description of two new genera and several new species of Mollusca, from the collection of Hugh Cuming, Esq. Proceedings of the Zoological Society of London. (1855) 23: 119-124. Available online at http://biodiversitylibrary.org/page/30748012 

Correa et al. 2010. Bridging gaps in the molecular phylogeny of the Lymnaeidae (Gastropoda: Pulmonata), vectors of Fascioliasis. BMC Evolutionary Biology 10:381. 

Dillon, R.T., Jr. and colleagues 2019.  The Freshwater Gastropods of North America.

Internet address: http://www.fwgna.org

Lamarck, J.B.M. (1799). Prodrome d'une nouvelle classification des coquilles, comprenant une rédaction appropriée des caractères géneriques, et l'établissement d'un grand nombre de genres nouveaux. Mémoires de la Société d'Histoire Naturelle de Paris. 1: 63-91., available online at http://biodiversitylibrary.org/page/13585626

Meier-Brook, C.,and Bargues M.D. 2002. Catascopia, a new genus for three nearctic and one palaearctic stagnicoline species (Gastropoda: Lymnaeidae). Folia Malacologica. 10(2): 83-84.

Vinarski M.V. 2012. The Lymnaeid genus Catascopia Meier-Brook et Bargues, 2002 (Mollusca: Gastropoda: Lymnaeidae), its synonymy and species composition. Invertebrate Zoology 9 (2):  P.91–104.