The mysterious purple mountain slug: first record of Deroceras juranum Wüthrich, 1993 (Gastropoda, Agriolimacidae) in France from the High Vosges mountains

The terrestrial slug Deroceras juranum Wüthrich, 1993, originally described as endemic to the Swiss Jura, was delineated primarily on the basis of its distinctive dark purple colouration and subtle penial-complex characters, which distinguished it from the closely related species Deroceras rodnae Grossu & Lupu, 1965, but the taxonomic status of D. juranum has since been revised, initially as a synonym and rare dark morph of the cream-coloured D. rodnae, and later as a distinct, colour-varying species based on sarcobelum characters and mating behaviour. Fieldwork in 2022 and 2024 around Lac de la Lauch in the High Vosges, France, allowed sampling of seven specimens with morphological and anatomical characters fully matching the original description of D. juranum. Comparative anatomical studies with topotypes from the Swiss Jura confirmed this nominal assignment, particularly with regard to reproductive anatomy, including sarcobelum characters consistent with those reported in subsequent literature. The recent discovery of the juranum morphotype in the Vosges mountains, possibly the dominant homozygous genotype, extends its range westwards and raises the question of the validity of the previous records of D. rodnae s.l. from eastern France. The High Vosges mountains currently represent the extreme north-western limit of the distribution of D. juranum, which is documented at its eastern edge as far as Austria and the Czech Republic. Further research is needed to determine the true taxonomic identity of the cream-coloured morph in the Vosges and French Jura which has been called D. rodnae.