Arion subfuscus (Draparnaud, 1805) is considered by some authors to be a partial synonym for Arion fuscus. Arion subfuscus (Draparnaud, 1805) and A. fuscus (Müller, 1774) have very similar morphology and have overlapping distributional ranges in northwestern Europe. Arion fuscus is widespread throughout Central, North and East Europe whereas A. subfuscus is restricted to West Europe. (For practical purposes the two are synonyms in Germany and in the Czech Republic.) The two taxa are referred to as the species complexArion subfuscus/fuscus both members having several evolutionary lineages. They are only separable by alloenzyme analysis and gonad type.
Description
A 50–70mm roundback slug. It is brown in colour, ranging from black-brown through olive-brown to orange and bright reddish-orange. Darker lateral bands are present. Dark pigment reaches under the pneumostome from back to front. The foot fringe is pale with thin lines. The sole is uniformly pale/translucent.The tentacles are pale or dark. It does not contract into a bell shape when stimulated. The Dusky Arion differs from other Arion species in its yellow-orange body mucus. Genitalia:Atrium about half diameter of spermatheca, spermatheca spherical, oviduct large and swollen like in Arion lusitanicus[3]
Distribution
This species occurs in European and Asian countries and islands including:
This slug lives on the ground, under fallen logs, rocks and under bark in woodland areas, but it can also take advantage of hedges, gardens, pastures, open fields, drier jack pine stands[12], yards, wetlands, forests and dunes. It is not as arboreal as the larger philomycid slugs.[11] It's habitat varies by season, in fall it forages in moist plant matter, in winter it burrows into the soil, in Spring it returns to the surface, In summer it seeks shelter to avoid desiccation.[13]
Diet
This slug is omnivorous and detritivorous. It will eat animal excrement, dead insects, fungi, yellowing foilage, dying plants, dead or dying worms, and fruit.[13][11]
Reproduction and Life Cycle
Like most land gastropods, Arion Fuscus is hermaphroditic and can both self fertilize and reproduce sexually depending on conditions. They generally live 8-12 months. It takes 4 weeks after fertilization to lay eggs, and they normally lay clusters of dozens of eggs at a time. Arion fuscus/subfuscus are semelparous and most adult arion subfuscus die shortly after reproduction but this can vary based on conditions. Generally eggs hatch sometime between autumn and winter, and adults die in summer. It is one of the species which may engage in Apophallation when penises become stuck together[13]
As Invasive Species
This species is the most widely introduced non-native slug in eastern North America, significantly outnumbering native species. Their flexible habitat requirements allow them to colonize more successfully than other slugs, and they may be able to hatch in autumn and become active in spring before other slugs who hatch in Spring. It may be a threat to the species calypso bulbosa and other early emerging native plant species in the Great Lakes region of the United States, and is the only slug active when it emerges. Further studies are necessary to confirm details[12]
Pinceel J., Joardens K., Van Houtte N., De Winter A.J. & Backeljau T. 2004: Molecular and morphological data reveal cryptic taxonomic diversity in the terrestrial slug complex Arion subfuscus/fuscus (Mollusca, Pulmonata, Arionidae) in continental north-west Europe. Biological Journal of the Linnean Society 83: 23–38. doi:10.1111/j.1095-8312.2004.00368.x
Pinceel J., Joardens K., Pfenninger M. & Backeljau T. 2005: Rangewide phylogeography of a terrestrial slug in Europe: evidence for Alpine refugia and rapid colonization after the Pleistocene glaciations. Molecular Ecology 14: 1133–1150. doi:10.1111/j.1365-294X.2005.02479.x
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