Towards a new standard in slug species descriptions: the case of Limax sarnensis Heim & Nitz n. sp. (Pulmonata: Limacidae) from the Western Central Alps

Abstract

The terrestrial slug Limax sarnensis Heim & Nitz new species is described from morphological and molecular characters, based on 298 specimens from 64 localities. Detailed descriptions of coloration, reproductive anatomy, distribution and ecology are provided. The new species differs from all other sympatric congeners by a diagnostic combination of characters: variable coloration of body with unicoloured mantle; outer fields of tripartite sole light grey to nearly black, fading from posterior to anterior and from outer edges to unpigmented middle field; penis dimension in preserved specimens about one-third to half of body length; penis interior with small transverse riblets, one longitudinal interior crest, a transverse penial crest and one longitudinal interior cord; copulates on a slime thread. It is restricted to inner alpine habitats in Switzerland and northern Italy. Phylogenetic analysis of 47 Limax specimens and outgroups using 1317 nucleotides of the cytochrome c oxidase subunit I gene supports the recognition of L. sarnensis as a new species. Limax alpinus Ferussac, 1822, becomes a junior synonym of Limax cinereoniger Wolf, 1803, by the designation of a neotype. Genotypic and phenotypic data are concordant with copulation (behavioural observations). The combination of morphological, genetic, ecological and behavioural data should set a new standard in slug species