The Arion hortensis complex, with notes on A. intermedius normand (Pulmonata: Arionidae)

A general study has revealed three distinct species commonly known as Arion hortensis Férussac, here referred to as A, R and B. After observation in natural habitats and in captivity for more than eight years, their essential differences are described, including differences in their external morphology and pigmentation, genital anatomy, shape of spermasophores, and mating behaviour. There is no evidence of interbreeding. In both seasonal and geographical distribution, A is the least restricted, and B the most restricted of the three species in the British Isles. A. intermedius Normand shares the main characters of the group, but critical differences are described.
Evidence is presented that the name hortensis Férussac, 1819 should be restricted to species R. The correct names for species A and B remain uncertain pending further research by the author.