**_Arion transsylvanus** (Mollusca, Pulmonata, Arionidae): rediscovery of a cryptic species
Faculty of Sciences. Biology
Zoologica scripta: an international journal of evolutionary zoology. - Stockholm
, p. 343-362
University of Antwerp
Cryptic species are abundant among invertebrates and are often hard to recognise. Molecular markers are an extremely useful tool to delineate cryptic taxa, although they should be applied with caution because different genes and techniques may yield different outcomes. We illustrate how cross-validation by molecular and morphological data can be applied to optimise taxonomic interpretations when cryptic species are involved. This is performed for the terrestrial slug Arion subfuscus species complex which represents a historical 'taxonomic garbage can'. Gonad morphology, allozymes and mtDNA data consistently showed that slugs from Romania and a location in E Poland represent a strongly differentiated taxon within this complex. These slugs are therefore formally redescribed and assigned to A. transsylvanusSimroth 1885; a forgotten nominal taxon from Transylvania. Diagnostic characters, including DNA sequences for the mitochondrial 16S rDNA are presented. Animals with the morphology of A. brunneusLehmann 1862, a nominal taxon which has also been reported from Romania, have the gonad type, allozyme alleles and 16S rDNA haplotypes of either A. fuscus, A. subfuscus or A. transsylvanus. Therefore, A. brunneus is regarded as a colour morph shared by several species and hence, A. transsylvanus is probably the only A. subfuscus-like species in the Romanian Carpathians.