About Arion hortensis A.Férussac, 1819
For slugs, it is often difficult to establish reliable criteria to identify species using either external or internal features. Coloration can be quite variable, and relatively plastic anatomy makes it hard to define clear diagnostic anatomical features. To distinguish this species from Arion distinctus, see the article on Arion distinctus. The clearest identifying character for Arion hortensis is the structure at the entrance to the epiphallus. Arion hortensis is a roundback slug that grows 30–40 mm long, and can reach up to 50 mm exceptionally. Its base color ranges from grey to bluish black, with dark lateral bands; the right band usually runs entirely above the pneumostome. Its tentacles are bluish or reddish, and the tail tip is bluish or orange. The first row of tubercles above the foot-fringe is white. When contracted, its body has a semicircular transverse section, and is not bell-shaped. Its foot sole is orange or yellow, and its body mucus is yellow-orange. Juveniles are bluish grey with a darker dorsum and a yellow sole. This species is native to European countries and islands, including Great Britain and Ireland. It has also been introduced to other regions across the world, including Tasmania. It inhabits gardens, fields, pastures, and similar open habitats, and acts as an intermediate host for Muellerius capillaris.
