Musings On A Local Specimen Of Toxolasma paulum (I. Lea, 1840), The Iridescent Lilliput
By Harry G. Lee

    Attached to leaf dredged from the bottom of Big Davis Creek (tributary of Julington Creek) adjacent to U. S. Route 1 just north of  Bayard, southeastern Duval County, Florida. Collected by Bill Frank, 3/11/2006. Six millimeters.
   Identifying tiny clams can be a difficult proposition for even the most experienced collector, and freshwater species are no exception. Although small enough to be an adult Pea Clam, Fingernail Clam, or even a Corbicula, the non-commarginal (not parallel to growth lines) rugged beak sculpture manifest only on the umbones on this specimen is unique to the superfamily Unionoidea, or pearly freshwater mussels. These are the species known to occur in the four Northeast Florida counties:

Anodonta couperiana I. Lea, 1840 Barrel Floater
Elliptio ahenea (I. Lea, 1847) Southern Lance
Elliptio jayensis (I. Lea, 1838) Florida Spike
Elliptio crassidens (Lamarck, 1819) Elephant Ear
Elliptio monroensis (I. Lea, 1843) St. John's Elephant-ear
Elliptio occulta (I. Lea, 1843) Hidden Spike
Elliptio waltoni (B. H. Wright, 1888) Florida Lance
Toxolasma paulum (I. Lea, 1840) Iridescent Lilliput
Uniomerus carolinianus (Bosc, 1801) Florida Pondhorn
Villosa amygdala (I. Lea, 1843) Florida Rainbow
Villosa vibex (Conrad, 1834) Southern Rainbow
Villosa villosa (B. H. Wright, 1898) Downy Rainbow
Utterbackia imbecillis (Say, 1829) Paper Pondshell [non-indigenous]

Based on the "single loop" pattern, the following can be ruled out

Villosa amygdala (I. Lea, 1843) Florida Rainbow
Villosa vibex (Conrad, 1834) Southern Rainbow
Villosa villosa (B. H. Wright, 1898) Downy Rainbow

Leaving:

Anodonta couperiana I. Lea, 1840 Barrel Floater
Elliptio ahenea (I. Lea, 1847) Southern Lance
Elliptio jayensis (I. Lea, 1838) Florida Spike
Elliptio crassidens (Lamarck, 1819) Elephant Ear
Elliptio monroensis (I. Lea, 1843) St. John's Elephant-ear
Elliptio occulta (I. Lea, 1843) Hidden Spike
Elliptio waltoni (B. H. Wright, 1888) Florida Lance
Uniomerus carolinianus (Bosc, 1801) Florida Pondhorn
Toxolasma paulum (I. Lea, 1840) Iridescent Lilliput
Utterbackia imbecillis (Say, 1829) Paper Pondshell

Of these the shell outline, which can change somewhat with growth (allometry), is only consistent with two species:

Uniomerus carolinianus (Bosc, 1801) Florida Pondhorn
Toxolasma paulum (I. Lea, 1840) Iridescent Lilliput

    The habitat is much more consistent with U. carolinianus, which, unlike the Iridescent Lilliput, has been taken in Duval Co., so I examined my adult specimens. Unfortunately, even though they are grand shells, they are eroded at the beaks, and no sculpture is apparent. Thence I went to my library and, after some disappointing false starts, found Johnson (1972). He reported that the beak sculpture of this species consists of " five or six heavy ridges that form a rounded angle on the posterior ridge ..." The juvenile shell's posterior is characterized in very precise lingo (for us musselheads), and it essentially rules out this species.

    Next I read Johnson's description of the beak sculpture of the Iridescent Lilliput. He reported "several ridges parallel to growth lines," which struck me as (1) not what our shell showed (noncom-, as opposed to commarginal) and (2) inconsistent with my accumulated conchological observations on various species and the few illustrations of unionoidean beak sculpture I had seen.

    What to do? Tempted to throw up my hands, I nevertheless went back to the collection and pulled my Iridescent Lilliputs. They have well-preserved beak sculpture! Not only that, the early shell is identical to the specimen in question. The faint rays on the specimen help confirm the Toxolasma paulum diagnosis - as does the bluish suffusion on the posterior region.

    While this species has not previously been documented from Duval County, it has been found in sixteen stations in the St. Johns River system - of which this creek is a part.

    Knowing that “paulus –a –um” was an adjective meaning small, I felt the specter of my high school Latin teacher, Mrs. Ewing, looking over my shoulder. Expecting gender agreement between genus and adjectival species names, I had winced countless times when confronted with the binomen "Toxolasma paulus" as it appears in the vast majority of modern publications on naiads (e. g., Turgeon, Quinn, et al., 1998). My presumption was, since the word ended in an "a," that genus name was likely a feminine noun consistent with Mrs. Ewing's rule regarding "a" terminations. I also recalled that a substitute Latin I teacher, Mr. Cornish, shared a mnemonic "L-A-N-C-E-T" for the terminations of irregular neuter nouns. Further confused by the fact that certain "-a" nouns of the first declension, e.g., agricola (farmer), nauta (sailor), were masculine, I realized that the wincing may have been unnecessary. If I was going to be certain, the only recourse was in a little research, which I began three years ago.

    Since the word Toxolasma doesn't appear in Latin dictionaries, I re-read the pages written by Constantine Samuel Rafinesque (1831), the author of Toxolasma. Of the new taxon he wrote: "Differs from Amblema, Plagiola, and Sintoxia, by lamellar tooth not obliqual but arched parallel with the back, axis nearly terminal, general form rounded, back curved." [my underlining; his punctuation and neologism]. As was customary in that era, he didn't directly indicate the gender of his new genus name, but the five species-level taxa he used in combination (fuscata, lutescens, cinerescens, lividus, and flexus) are feminine, collective, collective, masculine, and masculine respectively). Although generally consistent and correct with genus-species gender agreement, it appears that he sometimes failed to change the termination of established species names he transferred from the genus Unio (masculine) to his new genera, He was OK with Eurynia (feminine) but wrong (masculine) with Obliquaria - all within three pages of the description of Toxolasma. Thus Rafinesque fails to unequivocally provide the gender of the genus name Toxolasma.

    I then asked for help on the Internet list-serve Conch-L. My only substantive response came from Greek malacologist, George Sangiouloglou, who emailed me back: "In the Greek toxo means bow, arch. In synthetic words in Greek, when there are two [succesive] vowels, usually we remove [the second], so probably the Toxolasma is a synthetic word from Toxo-elasma. Another meaning of elasma is sheet of metal which has elasticity. I looked to the dictionary for the word lasma or lasmos; also I asked a friend with whom I studied Greek philology in the University, but we didn't find this word. In any case the gender for elasmos is masculine; elasma is feminine, and elasmon is neutral [sic]. There is in [modern] dictionary the word elasma which means write plate, sheet (of metal). Maybe the elasma is the root of this word."

    Thus we had a very plausible construct for the word "Toxolasma" consistent with the intent of its author - a bow (as in archery) plate, referring to the lateral tooth, which is arched (like a tensely-drawn bow). Apparently the elision of the "e" of elasmos/elasma is apparently not limited to the suffix situation. The Appalachian landsnail Ventridens lasmodon (Phillips, 1941) was translated as "lamina tooth." by Henry A. Pilsbry (1946: 457-458). Pilsbry (1939-1948) translated this from the Greek, as he did in very many of his species treatments, including the Cyrillic rendition of the word, as "lamina tooth."  I have collected this snail on a few occasions. The name is apt.

    Feeling I better understood the etymology and meaning of the word "Toxolasma," I entered a phase of gender-complacency and abandoned the probe until Bill Frank collected this little critter and Kurt Auffenberg asked me to review a manuscript. There it was again, the hauntingly incongruous "Toxolasma paulus" - twice. Something had to be done!

    Feeling the need for more gender-evidence, and realizing I hadn't exploited my electronic resources, on May 1, 2006 I Googled the more frequently-cited, but equally gender-bent, congener, Toxolasma parvus, (process and results underlined)! It was a bit like a slot-machine jackpot; there was an expected deluge (hits): Toxolasma parvum (35), Toxolasma parva (115), and Toxolasma parvus (353). So there was still discord in gender, and the (still incongruous) masculine proponents were in the lead. Impelled to push this electronic campaign, I went the work of Gary Rosenberg, who has a scientific name gender dictionary at his Malacolog database at the Academy of Natural Sciences of Philadelphia (ANSP - and coincidentally home to some of Rafinesque's collection). There I got no hits with a "*lasma" inquiry. Next I went to the ANSP Indo-Pacific database, which produced three genera, which I then Googled. Incorporating primary, secondary, tertiary, and quaternary generations of searches, and pretty-much limiting my report to unambiguous adjectival species-level epithets, I got:

Thiaridae: Sermylasma: S. retracta Iredale, 1943, S. venustula (Brot, 1877) [genus consistently treated as feminine]

Polyplacophora: Cryptoconchidae: Glyptelasma Iredale and Hull, 1925 (a junior homonym of Glyptelasma Pilsbry, 1907; regarded as a subgenus of Megalasma [q.v.] presently): G. carinatum (Hoek, 1883), G. hamatum (Calman, 1919) [genus consistently treated as neuter].

Polyplacophora: Ischnochitonidae: Callistelasma Iredale and Hull 1925: C. meridionalis hesperia Iredale and Hull, 1925, C. periousia Iredale and Hull, 1925 [The only clearly adjectival epithet is "meridionalis;" ambiguous masc./fem., but not neuter].

Crustacea: Cirripedia: Megalasma Hoek, 1883: M. subcarinatum Pilsbry, 1907, M. caudata, M. striatum Hoek, 1883, M. gracile (mentioned only in reference to a subspecies gracilus [noun] Pilsbry, 1907 in Clench and Turner, 1962), M. minus Annandale, 1906. [genus consistently treated as neuter].

    Although a heterogeneous lot, the usage by Pilsbry for his barnacle, Megalasma subcarinatum, brought to mind his elaborate land snail etymologies. It looked like neuter, trailing badly in the 35-115-353 sweepstakes, was due a lot more respect.

    Somewhat stunned at the outcome, I felt the need to return from cyberspace to the basic print literature. I again looked at the "bible," Brown's Composition of scientific words. On page 297 was "elasma; elasmos, Gr. metal plate; see plate," just as I recall it did on several previous passes - uninformative on gender. However, on this pass I went, as suggested to "plate" (p. 616) for the first time and found: "Gr. elasma, -tos, n.; elasmos m. metal plate: ..... Streptalasma profundum (a fossil coral)." The text and example clearly indicated -lasma was neuter. Brown and Pilsbry agreed!

    I think the case for neutering Toxolasma Rafinesque, 1831 is now powerful enough impel a rewrite on my labels. Let it be Toxolasma parvum (Barnes, 1823) and T. paulum (I. Lea, 1840) - hopefully putting an end to a Blefuscuan palaver over the Lilliputs, an apt name for the genus containing the very smallest naiads on Earth. **

    In this analysis there are several instances which demonstrate malacology to be, like all of science, a dynamic, self-correcting process, one which is built on the labors of our worthy predecessors, yet, through new discoveries, borrowed disciplines, and plain curiosity, inexorably advances - more often than not in unanticipated directions. Among the lessons learned in such a travail is to avoid reliance on any "fact," in the literature or on the Internet, unless it is accompanied by compelling evidence. Googling is like riding a locomotive, you go fast and can get almost anywhere, but you'd better be certain you have the right ticket lest you get off-track and debark at the wrong station.

Binney, W. G. and G. W. Tryon, Jr., 1864. The complete writings of Constantine Smaltz [sic] Rafinesque on Recent and fossil conchology.  Bailliere Bros., New York. pp. 1-96 + index pp. 1-6 + pls. lxx-lxxii. [see Rafinesque; a facsimile was published in 1984].

Brown, R. W., 1956.  Composition of scientific words. Smithsonian, Washington and London. pp. 1-882.

Clench, W. J. and R. D. Turner, 1962.  New names introduced by H. A. Pilsbry in the Mollusca and Crustacea. Acad. Nat Sci. Phila. Special Publication 4: 1-218.

Johnson, R. I., 1972.  The Unionidae (Mollusca: Bivalvia) of peninsular Florida. Bull. Florida State Museum Biol. Sci. 16(4): 181-249 June 5

Pilsbry, H. A., 1907. The barnacles (Cirripedia) contained in the collections of the United States National Museum. U. S. Nat. Mus. Bull 60: i-x, 1-122, figs. 1-35, pls. 1-11. [not seen].

Pilsbry, H. A., 1939 Land Mollusca of North America north of Mexico vol. I part 1. Academy of Natural Sciences, Philadelphia. xvii + 1-573 + ix. Dec. 6.

Pilsbry, H. A., 1940. Land Mollusca of North America north of Mexico vol. I part 2. Academy of Natural Sciences, Philadelphia. vi + 575-994 + ix. Aug. 1.

Pilsbry, H. A., 1946. Land Mollusca of North America north of Mexico vol. II part 1. Academy of Natural Sciences, Philadelphia. vi + 1-520. Dec. 6.

Pilsbry, H. A., 1948. Land Mollusca of North America north of Mexico vol. II part 2. Academy of Natural Sciences, Philadelphia. xlvii + 521-1113. Mar. 19.

Rafinesque, C. C., 1831. Continuation of a monograph of the bivalve shells of the River Ohio and other rivers of the western states. Privately published, Philadelphia. 8 pp. [not seen; see Binney and Tryon].

Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams, 1998.  Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks, 2nd edition. American Fisheries Society, Special Publication 26, Bethesda, Maryland. ix + pp. 1-509 + 16 pls. (unpaginated).

Appendix:

These are the species of Toxolasma parsed according to the new gender analysis:

T. corvunculus (noun in apposition; no change from current usage)
T. cyllindrellus (noun in apposition; no change from current usage)
T. lividum
T. mearnsi
(genitive; no change from current usage)
T. parvum
T. paulum
T. pullus
(noun in apposition; no change from current usage)
T. texasense

**Epilogue: Completing the loop two and a half months after Bill's find, Dr. Patrick Baker of the Institute for Food and Agricultural Studies, University of Florida collected near Bill's find and took several inch-long adult animals for the first time in Duval Co. See: http://www.jaxshells.org/parvumg.htm

Back