The Orculella species of the South Aegean island arc, a neglected radiation (Gastropoda, Pulmonata, Orculidae)

The genera Orcula Held, 1837, and Orculella Steenberg, 1925, can clearly be diagnosed anatomically (Hausdorf, 1996). In addition there are slight conchological differences. In Orcula, the apex of the shell is more or less depressed conical, whereas it is more domed in Orculella. More useful as a diagnostic character is a difference in sculpture of the protoconch whorls. In Orculella these whorls have prominent spiral striae, whereas in Orcula they are devoid of any distinct sculpture. Orculella cannot be separated conchologically from Sphyradium Charpentier, 1837, and Schileykula Gittenberger, 1983, however. The genus Orculella is particularly speciose in the Cyrenaica in N. Libya (Brandt, 1956) and Asia Minor (Hausdorf, 1996). More isolated species are known from elsewhere in the Mediterranean area, e.g. Sicily (Hausdorf, 1988) and N. Morocco (Gittenberger, 1983: 334). Exceptionally widespread is or was O. bulgarica (Hesse, 1915), which is not known from Greece, but has been reported, partly from Holocene deposits only, from Spain, Bulgaria, Turkey, Caucasian Russia, Armenia and Azerbaijan (Bank, 1986; Gittenberger, 1983: 329; Hausdorf, 1996: 15). Such a disjunct pattern is exceptional in western Palaearctic gastropod species.