The Six Euconulus Species Of The Eastern United States

Original digital images by David Kirsh with image editing by Bill Frank

Upper row L to R:  E. praticola (Reinhardt, 1883) Marsh Hive, Bennington Co., VT: max. height (H) 2.1 mm, max. width (W) 2.8 mm, 5.2 whorls; E. fulvus (Müller, 1774), Brown Hive, Bennington Co., VT: H 3.2 mm, W 3.4 mm, 6.5 whorls; E. polygyratus (Pilsbry, 1899), Fat Hive, Bennington Co., VT: H 2.4 mm, W 2.75 mm, 6.8 whorls.
Lower row L to R:  E. chersinus (Say, 1821), Wild Hive, Duval Co., FL: H 2.35 mm, W 2.5 mm, 6.8 whorls; E. dentatus (Sterki, 1893), Toothed Hive,  Jackson Co., FL: H 2.75 mm, W 2.5 mm, 6.9 whorls; E. trochulus (Reinhart, 1885), Silk Hive, Duval Co., FL: H 2.4 mm, W 2.45 mm; 6.6 whorls.

The Six Euconulus Species Of The Eastern United States

The Six Euconulus Species Of The Eastern United States

    The genus Euconulus, known as Hives in the vernacular, has always been an irksome taxon for collectors of eastern American landsnails. There are fewer characters than usual available for analysis as the shells are, at first glance, lacking in sculpture and of a monotonous size and shape as adults. This predicament is aggravated by various degrees of allometric shell growth and a predominance of juvenile shells in most suites. Distinctions among species are subtle and not usually explicit in the literature. Because of these barriers to species-level identification, published identifications and distributions are open to skepticism in many instances.
    On the other hand, limiting observations to adult shells, one may distill characters as species-level indicators: profile in apertural view, tightness of coil (apical view), shell surface (luster/texture/microsculpture/coloration), and the presence of internal "teeth" - the latter albeit in only one species.
   
Nekola (2004: 29, 31) seems to have been the first to recognize a “trichotomy” in northern US Euconulus. Analyzing a phenomenal 242 sites personally collected in NE Wisconsin and the adjacent southern Upper Peninsula of Michigan (slightly overlapping the latitude of Bennington Co., VT), he recognized the European species E. alderi, along with E. fulvus and E. polygyratus. The last of these was for years regarded as a subspecies of E. chersinus.* Reconciliation of Nekola’s descriptions with the figures and text of Pilsbry (1946: 235-242) and the British work by Kerney and Cameron (1979: 148-149) indicates that the same three names were applicable to the Vermont snails figured in the "northern" (upper) row of each panel above. E. alderi is dark, shiny, and has a low profile; E. fulvus (also see page two) is taller, paler, and more matte in texture; and E. polygyratus has a rounder profile and tighter coil than the other two. Although Nekola and others, e.g., Kerney and Cameron 1979 and Grimm 1996, used the name Euconulus alderi (Gray in Turton, 1840) for this Holoarctic species, G. Falkner et al. (2002) recently treated E. alderi as a synonym of E. trochiformis (Montagu, 1803), a European forest-dwelling species, and resurrected the name E. praticola (Reinhardt, 1883) for this dark, flat, glossy wetland species. R.G. Forsyth of the Royal British Columbia Museum, Vancouver, Canada followed Falkner et al. and dubbed it the "Marsh Hive" since it was not  treated in Turgeon, Quinn, et al. (1998). Inasmuch as "praticola" means "dweller in fields," its brand new vernacular name is much more apt than the "scientific" one.
<http://www.livinglandscapes.bc.ca/upperfraserbasin/ufb_snails/family2.html>
    Likewise, among the "southern" species in the lower row of each panel: E. chersinus is more cinnamon-colored than E. trochulus,** which is less tightly-coiled and has a less convex base. E. dentatus*** is tightly coiled like E. chersinus but has a uniquely tapering profile in contrast to the more triangular outlines of the other two taxa. The internal teeth of the aptly-named E. dentatus (as seen at Euconulus dentatus (Sterki, 1893) Toothed Hive) may be absorbed by the adult animal. Similarly these structures may be obscured or eroded in less-than pristine shells of any size, but it appears this feature is not essential for the identification of adult material.
    The extremely fine spiral sculpture of these species is best seen in E. praticola This character may eventually be analyzed in all six taxa with SEM but will not be further discussed at present.
* Hubricht (1965: 5) elevated it to specific rank.

** E. polygyratus was considered subordinate to E. fulvus or E. chersinus for three-quarters of a century until given full species rank by (Grimm, 1971: 53).

***
Like the preceding two captioned taxa, treated as a subspecies (of E. chersinus) from the time of its description until Hubricht (1983: 13) raised it to a full species.

Falkner, G., T.E.J. Ripken, and M. Falkner, 2002. Mollusques  continentaux de France, Liste de référence annotée et bibliographie. Patrimoines Naturels 52 (Muséum National d'Histoire Naturelle, Paris): 1-350.

Grimm, F.W., 1971. Annotated checklist of the land snails of Maryland and the District of Columbia. Sterkiana 41: 51-57.

Grimm, F.W., 1996. Terrestrial molluscs.  in I. M. Smith [ed.], Assessment of species diversity in the mixedwood plains ecosystem. EMAN (Environmental Monitoring and Assessment Network). CDROM <http://www.naturewatch.ca/mixedwood/landsnai/lsnail8.htm>.

Hubricht, L., 1965. Four new land snails from the southeastern United States. The Nautilus 79(1): 4-7.

Hubricht, L., 1983. Five new land snails from the southeastern United States, with notes on other species. Gastropodia 2: 13-19.

Kerney, M.P. and R.A.D. Cameron, 1979.  A field guide to the land snails of Britain and northwest Europe. Collins, London. Pp. 1-288 + 22 color plates.

Nekola, J.C., 2004. Terrestrial gastropod fauna of northeastern Wisconsin and the southern upper peninsula of Michigan. American Malacological Bulletin 18(1-2): 21-44. May 7.

Pilsbry, H. A., 1946. Land Mollusca of North America (north of Mexico) vol. 2 part 1. Academy of Natural Sciences, Philadelphia. vii + pp 1- 520. Dec. 6.

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.

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