Systematics of the onchidiid slug Onchidina australis (Mollusca: Gastropoda: Pulmonata)

In an effort to clarify the species diversity of onchidiid slugs, the taxonomy of Onchidina australis (Semper, 1880) is revised using both molecular data and comparative anatomy. All data un ambiguously demonstrate that there is a single Onchidina species along the coast of eastern Australia. The anatomy is redescribed as well as the color variation, based on first-hand observations of live animals in the field. The natural history of O. australis is unique within the Onchidiidae; it lives above the tidal zone, in a fully terrestrial habitat. Important nomenclatural issues are addressed based on the examination of all type material available and careful analysis of all original descriptions. In particular, Paraoncidium chameleon (Brazier, 1886) is shown to be a junior synonym of O. australis. Because P. chameleon is the type species of Paraoncidium Labbé, 1934, the latter name becomes a junior synonym of Onchidina Semper, 1882. The diversity and distribution of Onchidina, which so far includes only 1 valid species, is discussed.