Reconciling comparative anatomy and mitochondrial phylogenetics in revising species limits in the Australian semislug Helicarion Férussac, 1821 (Gastropoda: Stylommatophora)

Helicarion Férussac, 1821 currently comprises four semislug species from south-eastern Australia (Tasmania to New South Wales). We comprehensively revise the taxonomy of this group based on comparative morphology and on the mitochondrial genes COI and 16S, provide a new generic diagnosis and revise species descriptions. Contrary to the previous classification, we found that Helicarion encompasses only two species, differentiated by anatomy and mitochondrial genetics. Both contain several divergent mitochondrial DNA lineages. Based on their rather inconsistent morphological differentiation and their allopatric to parapatric distribution, we suggest that these intraspecific lineages may be in a transient stage of speciation. The type species, Helicarion cuvieri (Férussac, 1821), is redefined to include populations from Tasmania, Victoria and southern New South Wales, as far north as Wyong. Helicarion niger (Quoy & Gaimard, 1832), Helicarion leopardinus Iredale, 1941 and Helicarion mastersi callidus Iredale, 1941 are now recognized as synonyms of H. cuvieri. Helicarion mastersi (Cox, 1868) is restricted to an area from north of Nowra to southern Sydney in New South Wales.