Arion hortensis group: Arion distinctus

Family

Arionidae

Species

Arion distinctus Mabille, 1868

Common name

Dark-face 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 called the Arion hortensis group, which is comprised of Arion hortensis, A. owenii and A. distinctus. The Arion hortensis group is typically 25-35 mm long, and is only distinguished by the morphology of the genitaliaGenitalia:
The reproductive structures of an animal. May refer to either male or female structure.
. These slugs have two color morphs (dark grey or bluish grey ) that are more common than the brownish morph. They possess dark lateral stripes, where the stripe on the right side of the animal encompasses 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). Like the body, 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.
are bluish grey with a contrasting pale yellow or orange sole. The animals have no keelKeel:
Also known as the carina. This is a longitudinal ridge that runs dorsally along the apex of the tail of the animal.
. Contracted specimens are rounded in cross-section. This group has a characteristic yellow-orange mucus. Molecular techniques can also be used to identify members of this group.

Genitalic characters used to distinguish the three species:

Arion distinctus: epiphallic structure conicalConical:
Shell shape: shells with an elongated spire that tapers to a point and are slightly broader at the base.
in cross-section, and covers the entire opening of the epiphallus.

Arion hortensis: epiphallic structure raised with "finger-like" projections, and only partially covers the opening of the epiphallus.

Arion owenii: epiphallic structure flattened and irregularly shaped, and does not cover the opening of the epiphallus.

Native range

Western Europe

Distribution

North America:

• U.S.: California, Pennsylvania
• Canada: Vancouver, Southern Vancouver Island, Halifax, near Ottawa and Kingston

Australasia: New Zealand

Europe

Ecology

This slugSlug:
A snail that either does not possess a shell or has one that is very reduced (no definite coiling) or internal.
consumes agriculturally important crops and often inhabit disturbed sites (e.g., gardens, roadsides). Arion hortensis and A. distinctus reproduce by cross fertilization. The means by which A. owenii reproduces has not been documented. In England, A. hortensis mates in the fall and winter while A. distinctus mates during spring and summer months. They can live up to one year.

Synonyms

• Arion hortensis of authors in part, not Férussac, 1819
• A. hortensis form 'A' of authors.

References

Davies 1977; Davies 1979; Grimm et al. 2009; Horsák 2004; Hunter 1966; Iglesias and Speiser 2001; Kantor et al. 2009; Roth and Sadeghian 2006