Morphological and molecular analysis of the status and relationships of the land snail “Cernuella” usticensis (Calcara, 1845) (Stylommatophora: Helicoidea)

The revision of 'Cernuella' usticensis, an helicelline hygromiid, was based on the analysis of morphological characters and on the genetic study of allozyme patterns. The morphological study demonstrates that C. usticensis can be distinguished from all the other Cernuella species by the presence of a dart sac complex with basal vaginal outgrowth, inner sac with thin walls and large lumen, and a less-developed 'dart-gun'. Analysis of allozyme polymorphisms. performed to test its relationships to other Cernuella species, namely C. virgata, C. cisalpina, C. caruanae, C. amanda and C neglecta confirms that 'C' usticensis is distinct from all those examined. Parsimony analysis of the morphological characters of all taxa included in the helicelline hygromiids (hygromiids with pedal innervation of penis) suggests that it forms a monophyletic group with Ichnusomunda based on the inner sac structure (with thin walls and large lumen). Unfortunately, material of the only species of Ichnusomunda. I. sacchii, was not available for allozyme analysis, and consequently it has not been possible to test this hypothesis genetically. Since homoplasies cannot be ruled out (inner sac with thin walls and wide lumen are known in other hygromiids), its inclusion in Ichnusomunda must await further evidence.