Phylogenetic relationships inferred from the sequence and secondary structure of ITS1 rRNA in Albinaria and putative Isabellaria species (Gastropoda, Pulmonata, Clausiliidae).

An analysis of the ITS1 sequence variation among five species of terrestrial pulmonate snails was performed to decide between two conflicting hypotheses concerning the phylogeny of these anatomically similar gastropods. It turned out that the so-called genus Isabellaria is a polyphyletic entity; the diagnostic, apomorphic structure of its clausilial apparatus, enabling a nearly complete obstruction of the shell aperture with the animal at rest, apparently evolved more than once from ancestors currently classified with the speciose genus Albinaria. The classification based on general shell shape and sculpture, and distributional patterns, turns out to be the natural one. This study also provides the first data on ITS1 sequences in gastropods. The recently published ITS1 sequence of another molluscan species, a bivalve, is quite different but similar in length to that of the snails.