Salients in distinguishing a pair of similar syntopic doorsnails

    In each panel below there is a pair of apparently left-handed (the familial norm) clausiliid snail shells. In each case the image on the left is an unaltered Albinaria (Isabellaria) lophauchena (Sturany, 1894), and the one on the right is a mirror image of a (normally-dextral) Nymphogena dextrosa (O. Boettger, 1877).

    The two were collected together, along with several other conspecifics, by Maria Demertzis in Greece: Voras Range, Mount Paiko, Pella Prefecture ca. 29 km SSW Giannitsa, 100 to 200 m. above end of access road, among limestone rocks along the trail to the peak.
A later sample from this station by Maria totaled 321 specimens. Of these 259 (80.4%) were sinistral and 62 (19.6%) were dextral.

    In apertural view A. lophauchena (L) and N. dextrosa (R) appear quite similar, but the acutely-tapered apex and small nuclear whorl of the latter is distinctive. Likewise the more callous peristome and larger, more horizontal "inferior lamella" [columellar fold; see arrows] of the former seem consistent rather than an ontogenetic (developmental) artifact of greater maturity.

   The dorsal view reveals substantial differences. The axial fold (lunella) A. lophauchena (L) is weakly sigmoid, whereas that of the mirror-imaged N. dextrosa (R) appears to have a rectangular flexure (actually due to fusion with a spiral lamella) making a pattern like the number "7" [horizontal arrows]. The spiral lamellae [vertical arrows] are poorly developed in A. l. while the "principal plica" of N. d. is extremely long, actually spanning half the body whorl and being clearly visible within the aperture. The ridge (crista) on the body whorl of A. l. is much more well-developed, is somewhat sinuous, and lies oblique to the shell axis (opisthocline) vs. the straighter coaxially-oriented crista of S. d. [oblique arrows].

    In these lateral views [left-lateral for the sinistral A. lophauchena (L) and right-lateral (mirrored to appear in the same orientation) for the dextral N. dextrosa (R)], the differences in placement of the lunellae (see oblique arrows and panel immediately above) is evident, but an equally conspicuous difference is the C-shaped [a backwards-C after mirroring] subcolumellar lamella [horizontal arrow] just inside the aperture of N. dextrosa. There is a homologous structure in A. lophauchena, but it is narrower, straight, and so close to the aperture that it cannot be seen in this view.

    The above conchological terminology conforms to that of Nordsieck (2007), and the taxonomic treatment follows Schileyko (2000).

Nordsieck, H., 2007. Worldwide Door Snails (Clausiliidae), Recent and fossil. ConchBooks, Hackenheim, Germany. Pp. 1-214. Oct.
Schileyko, A. A., 2000. Treatise on Recent terrestrial pulmonate molluscs 5. Clausiliidae. Ruthenica supplement 2: (ii) + 565-729 incl. numerous text figs. May.