When last we left our fearless jpeg naturalist, he had just
received several images of hydrobiid snails from Ms. Rachel Vinsel, the
curatorial assistant at the Illinois Natural History Survey. One image depicted cotypic Marstonia ozarkensis,
collected by A. A. Hinkley in 1914 from the White River drainage in northern
Arkansas [1], declared extinct by the US Fish & Wildlife Service in late
2018 [2]. That’s the first image in the
photomontage below, reprinted from last month’s essay.
Ah, but there were “several images” attached to Rachel’s late
February email. She went on to add:
“While I have you, I was wondering if you'd mind taking a look at image 0097 as well? This one was collected in the Kishwaukee River (Rock River Dr.) Winnebago Co., IL. It's not quite 3mm tall.”
 |
| All four approx 3 mm std length |
Holy crap, we have seen those little snails before. At this point, could I ask you all to indulge
me? Would you mind opening up my essay
of 19Jan16 in a new window? Here’s the
link:
In that charmingly-befuddled essay, you may remember my
fumbling with a mysterious population of 3 mm hydrobiid snails collected from
the muck of Lake St. Clair, 25 miles east of Detroit. Check out the photos in that essay, one of
which has been clipped and inserted third in the montage above. And now could I ask you to refer to my
follow-up essay of 5Feb16:
The matches between cotypic M. ozarkensis, Rachel’s
Kishwaukee unknown and the Lake St Clair Marstonia letsoni is pretty darn near
perfect, am I right? And let me add yet
another observation.
In January of 2017 I was combing through a remarkable set of
collections made by our good friend Ryan Evans up in Kentucky, when my eyes
fell on a single, tiny shell from Elkhorn Creek, about 10 km north of
Frankfort. That shell is depicted at the
far right of the montage above [3]. That’s
pretty good match as well, am I right?
So we have now established two things. In 2016, we demonstrated that populations of
Marstonia letsoni are quite literally obscure – tiny snails, inhabiting dark
recesses, sometimes in deep water. To
find one, you’d need to be more persistent or more lucky than I, your humble
correspondent, who has never seen one in his entire 45-year career combing the
lakes and rivers of America, overtly and deliberately committing premeditated
acts of freshwater malacology in the first degree.
And we have now documented that tiny, obscure hydrobiids of this general sort can have strikingly broad ranges. Lake St Clair is
500 km north of Frankfort, KY, and 500 km east of the Kishwaukee River at
Rockford, IL. Could Marstonia letsoni
range another 700 km to the Ozarks? Might Marstonia ozarkensis (Hinkley 1915) be
a junior synonym of Marstonia letsoni (Walker 1901)?
Let me make one final point in closing. All authors who have any first-hand experience
in this arcane little corner of malacology – Hinkley, Bob Hershler [4], and Shi-Kuei
Wu [5] – have been unanimous that in overall morphology and life habit, both
Marstonia ozarkensis and M. letsoni are very similar to a third species, Marstonia scalariformis. The primary distinction
is a carina or keel on the shell of scalariformis, which Wu and colleagues [4]
observe “may be absent or only vaguely apparent” in some natural
populations. See Wu’s Figures 26 – 29
below.
 |
| M. ozarkensis (26, 27) and M. scalariformis (28, 29) from Wu [5]. |
Marstonia scalariformis rivals M. letsoni in both obscurity
of life habit and vastness of range. Wolf
[6] described “Pyrgula” scalariformis in 1869 from a single shell found by the
banks of the Illinois River. Hinkley [7]
described wabashensis from the Wabash River at the Illinois/Indiana border in
1908, which Hershler [4] synonymized under scalariformis in 1994, noting “variable
carina development.” Hershler’s figure
of the penial morphology of scalariformis sampled from the Meramec River in
Missouri shows bifurcation reminiscent of the letsoni penis figured by Berry [8].
And the “very incompletely known” range of scalariformis
ranges all the way from central Illinois south down to tributaries of the
Tennessee River in north Alabama [9].
Hinkley thought that the previously-described species most similar
to his ozarkensis was wabashensis.
Hershler agreed, suggesting that wabashensis was a junior synonym of
scalariformis and adding further that letsoni was also most similar to
scalariformis, without directly comparing ozarkensis to letsoni. I am not sure here today whether Marstonia
ozarkensis (Hinkley 1915) is actually extinct, or if it was simply a local
population of what has been called elsewhere letsoni (Walker 1901), or wabashensis
(Hinkley 1908) or possibly even scalariformis (Wolf 1869), now here in the 21st
century misunderstood into oblivion.
Notes:
[1] Hinkley, A.A. (1915) New Fresh-water Shells from the
Ozark Mountains. Proceedings of the United States National Museum,
49:587-589. This is actually the 1916
volume of the PUSNM, but Hinkley’s date of publication is given as “December
23, 1915” in the index.
[2] USFWS 2018. Ozark
snail species presumed extinct following science-based surveys.
[3] Note subsequently added: The image at far right was originally labeled "Kentucky letsoni" in my post of 2020. After comparison with Marstonia populations in North Alabama, however, in 2022 I reidentified that little shell as Marstonia pachyta angulobasis.
[4] Hershler, R. (1994) A review of the North American
freshwater snail genus Pyrgulopsis (Hydrobiidae). Smithsonian Contributions to Zoology 554:
1-115.
[5] Wu, S-K, R. D. Oesch & M. E. Gordon (1997) Missouri
Aquatic Snails. Missouri Department of
Conservation, Jefferson City. 97 pp.
[6] Wolf, J. (1869)
Descriptions of three new species of shells.
American Journal of Conchology 5: 198.
[7] Hinkley, A. A. 1908. A new species of Pyrgulopsis. Nautilus 21: 117-118.
[8] Berry, E. G. (1943)
The Amnicolidae of Michigan: Distribution, ecology, and taxonomy. Misc. Publ. Mus. Zool. Univ. Mich. 57: 1 –
68.
[8] Walker, B. 1906. New and Little Known Species of
Amnicolidae. Nautilus, 19:114-117.
Walker identified the population collected by Mr. Hinkley near Florence,
Alabama, as “Pyrgulopsis mississippiensis (Pilsbry),” which is a junior synonym
of M. scalariformis, according to Hershler [4]. There are also museum records
of M. scalariformis from the Flint River near Huntsville that need
confirmation.
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