Arion subfuscus (Draparnaud, 1805) and A. fuscus (Müller, 1774) have very similar morphology and have overlapping distributional ranges in northwestern Europe.

The two taxa are referred to as the species complex Arion subfuscus/fuscus both members having several evolutionary lineages.

It is brown in colour, ranging from black-brown through olive-brown to orange and bright reddish-orange.

Genitalia:Atrium about half diameter of spermatheca, spermatheca spherical, oviduct large and swollen like in Arion lusitanicus[1] This species occurs in European and Asian countries and islands including: This slug lives under fallen logs and under bark in woodland areas, but it also lives in hedges, gardens, pastures and dunes.

Media related to Arion subfuscus at Wikimedia Commons