Arion is a genus of air-breathing land slugs in the family Arionidae, the roundback slugs.MolluscaBase eds. (2025). MolluscaBase. Arion A. Férussac, 1819. Accessed through: World Register of Marine * At: https://www.marinespecies.org/aphia.php?p=taxdetails&id=818149 on 2025-10-25

Most species of this Palearctic genus are native to the Iberian Peninsula.

Species can be difficult to distinguish from one another upon cursory examination, because individuals of a species can vary in color and there are few obvious differences between taxa.Skujienė, G. and M. Soroka. (2003). A comparison of different DNA extraction methods for slugs (Mollusca: Pulmonata). Ekologija 1, 12–16. The color of an individual can be influenced by its diet.

Some Arion are known as pests, such as A. lusitanicus auct. non Mabille (= A. vulgaris), which damages agricultural crops and ornamental plants, and A. rufus, a familiar garden pest.Soroka, M., et al. (2008). Distribution and genetic diversity of the terrestrial slugs Arion lusitanicus Mabille, 1868 and Arion rufus (Linnaeus, 1758) in Poland based on mitochondrial DNA. Folia Biologica 57(1–2), 1–2. Arion slugs are often transported internationally in shipments of plant products and mushrooms. Arion slugs have been identified in North America and Australia as invasive species, altering the plants of ecosystems through seed predation and competing with native slugs.

Species There are over 40 species in the genus.

Species include:

Arion amygdaliformis Castillejo, Baselga, Lorenzo-Carballa, Iglesias & Gomez-Rodriguez, 2024 Arion anthracius Bourguignat, 1866 Arion ater (Linnaeus, 1758) – black slug Arion ater rufus (Linnaeus, 1758) – red slug Arion atripunctatus Dumont & Mortillet, 1853 Arion baeticus Garrido, Castillejo & Iglesias, 1994 Arion circumscriptus Johnston, 1828 – brown-banded arion Arion distinctus Mabille, 1868 – darkface arion Arion euthymeanus Florence, 1886 Arion fagophilus de Winter, 1986 Arion fasciatus (Nilsson, 1823) – orange-banded arion Arion flagellus Collinge, 1893 Arion fuligineus Morelet, 1845 Arion fuscus (O.F.Müller, 1774) Arion gilvus Torres Mínguez, 1925 Arion hispanicus Simroth, 1886 Arion hortensis Férussac, 1819 – small striped slug Arion intermedius Normand, 1852 (syn. Arion alpinus Pollonera, 1887Manganelli, G., et al. (2010). The status of Arion alpinus Pollonera 1887, and re-description of Arion obesoductus Reischütz 1973 (Gastropoda, Arionidae). Journal of Conchology 40, 269–76.) – hedgehog slug Arion iratii Garrido, Castillejo & Iglesias, 1995 Arion lizarrustii Garrido, Castillejo & Iglesias, 1995 Arion luisae Borrèda & Martínez-Ortí, 2014 Arion lusitanicus Mabille, 1868 Arion magnus Torres Mínguez, 1923 Arion molinae Garrido, Castillejo & Iglesias, 1995 Arion nobrei Pollonera, 1889 Arion obesoductus (syn. Arion alpinus auctt. non Pollonera, 1887) Arion occultus R.Anderson, 2004 Arion owenii Davies, 1979 – warty arion Arion paularensis Wiktor & Parejo, 1989 Arion ponsi Quintana, 2007 Arion sibiricus Simroth, 1902 Arion simrothi Künkel, 1909: synonym of Arion (Mesarion) simrothi Künkel, 1909 (uncertain > taxon inquirendum, subgeneric affiliation unclear) Arion subfuscus (Draparnaud, 1805) – dusky arion Arion timidus Morelet, 1845 Arion torquiformis Castillejo, Baselga, Lorenzo-Carballa, Iglesias & Gomez-Rodriguez, 2024 Arion transsylvanus Simroth, 1885 Arion urbiae de Winter, 1986 Arion vulgaris Moquin-Tandon, 1855 (also referred to as Arion lusitanicus auct. non Mabille) – Spanish slug Arion wiktori Parejo & R. Martín, 1990

Synonyms Arion alpinus Pollonera, 1887: synonym of Arion intermedius Normand, 1852 (junior subjective synonym) Arion andersonii J. G. Cooper, 1872: synonym of Prophysaon andersonii (J. G. Cooper, 1872) (superseded combination) Arion anguloi Martín & B. Gómez, 1988: synonym of Arion urbiae de Winter, 1986 (a suggested synonym) Arion aterrimus L. Pfeiffer & J. E. Gray, 1855: synonym of Oopelta aterrima (L. Pfeiffer & J. E. Gray, 1855) (original combination) Arion austeniana G. Nevill, 1880 (nomen nudum) Arion coerulens Collinge, 1897: synonym of Arion distinctus Mabille, 1868 Arion cottianus Pollonera, 1889: synonym of Arion distinctus Mabille, 1868 Arion elongatus Collinge, 1894: synonym of Arion hortensis A. Férussac, 1819 Arion empiricorum A. Férussac, 1819: synonym of Arion ater (Linnaeus, 1758) (junior subjective synonym) Arion foliolatus A. Gould, 1851: synonym of Prophysaon foliolatum (A. Gould, 1851) (original combination) Arion hessei Simroth, 1894: synonym of Arion distinctus Mabille, 1868 † Arion hochheimensis Wenz, 1911 (apparently no gastropod but calcareous excretions of Lumbricidae) † Arion kinkelini Wenz, 1911 (apparently no gastropod but calcareous excretions of Lumbricidae) Arion minimus Simroth, 1885: synonym of Arion distinctus Mabille, 1868 Arion mollerii Pollonera, 1889: synonym of Arion distinctus Mabille, 1868 Arion rubellus Sterki, 1911: synonym of Arion hortensis A. Férussac, 1819 (junior synonym) Arion rufus (Linnaeus, 1758): synonym of Arion ater rufus (Linnaeus, 1758) (superseded rank) Arion silvaticus Lohmander, 1937: synonym of Arion circumscriptus silvaticus Lohmander, 1937 (superseded rank) Arion sulcatus Morelet, 1845: synonym of Arion ater (Linnaeus, 1758) (junior subjective synonym) Arion vejdovskyi Babor & Koštál, 1893 : synonym of Arion distinctus Mabille, 1868 Arion vejdowskyi Babor & Koštál, 1893 : synonym of Arion distinctus Mabille, 1868 Arion vejdorskyi : synonym of Arion (Microarion) vejdowskyi Babor & Koštál, 1893: synonym of Arion distinctus Mabille, 1868 Arion verrucosus Brevière, 1881: synonym of Arion intermedius Normand, 1852

Etymology The name Arion is in reference to Aelion's De Natura Animalium, which features a story about areíones - snails which leave their shells behind to feed, thus outsmarting predators who attack the empty shells.

Mentioning in literature and folklore Larger Arion slugs frequently appear in various forms of traditional culture, including folk traditions, children's rhymes, and historical documentation of their practical uses. In pre-industrial Sweden, there are historical accounts, like the one in Lorens Wolter Rothof's 1762 book, detailing the unusual practice of using the black slug (Arion ater) as a source of grease to lubricate wooden wagon axles.

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