Arion fasciatus group: Arion circumscriptus




Arion circumscriptus Johnston, 1828

Common Name

Brown-banded arion, White-soled slug


This slug belongs to a species complex that range in length from 30 to 40 mm as fully mature adults. This species-complex (Arion fasciatus group) contains the following species: Arion silvaticus, A. circumscriptus and A. fasciatus. Species in this group can be separated based on their genitalia. The body of the slugs is grayish centrally and white laterally with a pair of dark-colored stripes that run longitudinally. The stripes are often broken at the posterior edge of the mantle. The body often appears to have a granular texture. There may also be a slight reddish color to the dorsal surface of the animal. The slightly granular mantle is rusty-gray in color and lacks markings (except in Arion circumscriptus). The tentacles and head are black in color. The pneumostome (breathing pore) occurs in the anterior one-third of the slug's mantle on the right side of the body. In contracted individuals the body is bell-shaped. No keel is present in this group; however, an enlarged row of pale colored tubercles may create an impression that one may exist (false keel). As the common name (White-soled slug) suggests, the sole of this species-complex is pale colored, similar to the foot fringe. The mucus secreted by this group is colorless or yellow. Molecular techniques can also be used to identify members of this group.

Genitalic characters used to distinguish the three species:

Arion fasciatus: genitalia with a short atrium, a narrow oviduct and an unpigmented thick epiphallus.

Arion circumscriptus: genitalia with a long narrow atrium, a relatively narrow oviduct and a pigmented epiphallus.

Arion silvaticus: genitalia with a long atrium, a broad oviduct and an unpigmented narrow epiphallus.

Native Range



North America:

  • U.S.: Northern United States
  • Canada: Ontario, Quebec, Newfoundland, British Columbia


The slugs in the Arion fasciatus group are typically found in disturbed habitats; however, they commonly invade natural areas. The brown-banded arion (Arion circumscriptus) is primarily nocturnal. All three species have been reported in greenhouses and may become a serious agricultural pest. Reproduction is primarily through self-fertilization.


  • Arion bourguignati Mabille, 1868


Anderson 2005; Branson 1959; Hutchinson and Heike 2007; Grimm et al. 2009; Kantor et al. 2009; Kerney et al. 1979

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