Arion fasciatus group: Arion silvaticus

Family

Arionidae

Species

Arion silvaticus Lohmander, 1937

Common name

Forest arion

Description

This slugSlug:
A snail that either does not possess a shell or has one that is very reduced (no definite coiling) or internal.
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 genitaliaGenitalia:
The reproductive structures of an animal. May refer to either male or female structure.
. 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 posteriorPosterior:
Directional term: the rear or tail end of an animal.
edge of the mantleMantle:
A fleshy, membranous covering of the anterior portion of the body of a mollusc. It secretes the materials that form the shell.
. The body often appears to have a granularGranular:
Bearing granules on the surface or having a rough appearance.
texture. There may also be a slight reddish color to the dorsal surface of the animal. The slightly granularGranular:
Bearing granules on the surface or having a rough appearance.
mantleMantle:
A fleshy, membranous covering of the anterior portion of the body of a mollusc. It secretes the materials that form the shell.
is rusty-gray in color and lacks markings (except in Arion circumscriptus). The tentaclesTentacles:
Sensory projections on the head end of a mollusc. There are generally two pairs; upper (posterior) and smaller, lower (anterior). The upper pair bears the eyes. In many snails the eyes are located at the tips of this structure; however, in Basommatophoran snail species, the eyes are located at the base of the tentacles.
and headHead:
The area of a mollusc's body that has the tentacles, eyes and mouth.
are black in color. The pneumostomePneumostome:
This is the breathing hole on the right side of the mantle of molluscs. This allows air to pass through to the lung for gas exchange.(See also breathing pore).
(breathing pore) occurs in the anteriorAnterior:
Directional term: located in front. Nearer the head or front end of a shell.
one-third of the slug's mantleMantle:
A fleshy, membranous covering of the anterior portion of the body of a mollusc. It secretes the materials that form the shell.
on the right side of the body. In contracted individuals the body is bell-shaped. No keelKeel:
Also known as the carina. This is a longitudinal ridge that runs dorsally along the apex of the tail of the animal.
is present in this group; however, an enlarged row of pale colored tuberclesTubercles:
An enlarged or raised region on the body of a slug. The shape of this structure is very variable. (See also tubercle)
may create an impression that one may exist (false keelKeel:
Also known as the carina. This is a longitudinal ridge that runs dorsally along the apex of the tail of the animal.
). The sole of this species-complex is pale colored, similar to the footFoot:
The muscular organ on the undersurface of the body of a mollusc upon which the animal rests or uses to crawl.
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 Genitalia:
The reproductive structures of an animal. May refer to either male or female structure.
with a short atriumAtrium:
Opening or passage of the genitalia. OR Region for the reception of gametes.
, a narrow oviduct and an unpigmented thick epiphallus.

Arion circumscriptus: genitalia Genitalia:
The reproductive structures of an animal. May refer to either male or female structure.
with a long narrow atriumAtrium:
Opening or passage of the genitalia. OR Region for the reception of gametes.
, a relatively narrow oviduct and a pigmented epiphallus.

Arion silvaticus: genitalia Genitalia:
The reproductive structures of an animal. May refer to either male or female structure.
with a long atriumAtrium:
Opening or passage of the genitalia. OR Region for the reception of gametes.
, a broad oviduct and an unpigmented narrow epiphallus.

Native range

Europe

Distribution

North America:

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

Ecology

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 nocturnalNocturnal:
Occurring or becoming active at night.
. All three species have been reported in greenhouses and may become a serious agricultural pest. Reproduction is primarily through self-fertilizationSelf-fertilization:
This is an event where an organism is produced by the fertilization of an egg by sperm from the same organism. (See also hermaphrodite)
.

Synonyms

• Arion fasciatus of authors, in part, not Nilsson, 1823
• Arion circumscriptus var. silvaticus Lohmander, 1937

References

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