Arion distinctus

Arion hortensis was described by Férussac in 1819.{{cite book |last1=Férussac |first1=J. B. L. d'Audebard de |title=Histoire naturelle générale et particulière des mollusques terrestres et fluviatiles 2 |date=1819 |page=196}} Only in the 1970s did the amateur malacologist Stella Davies discover that in Britain that name had been applied to three distinct species.{{cite journal |last1=Davies |first1=S.M. |title=The Arion hortensis complex with notes on A. intermedius Normand (Pulmonata: Arionidae) |journal=Journal of Conchology |date=1977 |volume=29 |pages=173–187}} Later the name Arion distinctus was used for the one of these species that Davies had provisionally called "form A".{{cite journal |last1=Davies |first1=S.M. |title=Segregates of the Arion hortensis complex (Pulmonata: Arionidae), with the description of a new species, Arion owenii |journal=Journal of Conchology |date=1979 |volume=30 |pages=123–127}}{{cite journal |last1=Winter |first1=A.J. de |title=The Arion hortensis complex (Pulmonata: Arionidae): designation of types, descriptions, and distributional patterns, with special reference to the Netherlands |journal=Zoologische Mededelingen |date=1984 |volume=59 |issue=1 |pages=1–17}} Mabille's original 1868 description of A. distinctus{{cite book |last1=Mabille |first1=J. |title=Archives malacologiques, Troisième fascicule. Des Limaciens européens. Zonites dutaillyanus| date=1868 |location=Paris |publisher = F. Savy| pages=33–54}} included details (colouration, date of collection) that tended to indicate this species rather than Arion hortensis s.s. No type survived, so a neotype has been designated, collected from the same rough locality (near Sèvres, Paris).

As in other members of the genus Arion, the pneumostome is in the anterior half of the mantle. Arion distinctus never gets bigger than about 4 cm extended.{{cite book |last1=Rowson |first1=Ben |last2=Turner |first2=James |last3=Anderson |first3=Roy |last4=Symondson |first4=Bill |title=Slugs of Britain and Ireland: identification, understanding and control |date=2014 |publisher=Field Studies Council |location=Telford|isbn=978-1-908819-13-0}} In contrast with members of the subgenus Carinarion (e.g. Arion circumscriptus), there is no dorsal line of pale tubercles suggesting a keel and the shape of the body in cross-section is a segment of a circle rather than a bell shape.{{cite book |last1=Kerney |first1=M.P. |last2=Cameron |first2=R.A.D. |title=A Field Guide to the Land Snails of Britain and North-West Europe |date=1979 |publisher=Collins |location=London |isbn=978-0002196765}} Arion distinctus lacks the prickly tubercles of A. intermedius, and is larger and darker with prominent lateral bands. Arion subfuscus and A. fuscus can look similar to A. distinctus when preserved, but these species in life have bright orange mucus on the body and a pale sole, whereas in A. distinctus the sole appears yellow or orange from the sole mucus, but the body mucus is not coloured.

However, reliable discrimination from other members of the subgenus Kobeltia is not always straightforward on external characters. In much of Western Europe the Kobeltia species most likely to be confused is A. hortensis; mixed populations often occur. Authorities differ in their advice on how reliably the two species can be separated using external characters when alive.{{cite book |last1=Barker |first1=G.M. |title=Fauna of New Zealand 38: naturalised terrestrial Stylommatophora |date=1999 |publisher=Manaaki Whenua Press |location=Lincoln, New Zealand |isbn=978-0-478-09322-3}}{{cite journal |last1=Iglesias |first1=J. |last2=Speiser |first2=B. |title=Distribution of Arion hortensis s.s. and Arion distinctus in northern Switzerland |journal=Journal of Molluscan Studies |date=2001 |volume=67 |issue=2 |pages=209–214|doi=10.1093/mollus/67.2.209|doi-access=free }} Useful indications are that A. distinctus has dark tentacles without the red or violet tinge typical of A. hortensis, the general appearance of its back is yellower or browner than in A. hortensis, the row of tubercles directly above the sole is not as white as is typical of A. hortensis, and (least reliably) the lateral bands tend to be lower, running through the pneumostome rather than above. If dissection reveals a two-partite oviduct, one can be sure of A. distinctus, but in most regions a sizeable proportion of individuals have a three-partite oviduct like that of A. hortensis. The definitive character, distinguishing A. distinctus from all other Kobeltia species, is a conical structure inside the atrium that covers the entrance to the epiphallus,{{cite journal |last1=Backeljau |first1=T. |last2=Van Beeck |first2=M. |title=Epiphallus anatomy in the Arion hortensis species aggregate (Mollusca, Pulmonata) |journal=Zoologica Scripta |date=1986 |volume=15 |pages=61–68 |doi=10.1111/j.1463-6409.1986.tb00209.x |s2cid=84574780 }}{{cite journal |last1=Dvořák |first1=L. |last2=Backeljau |first2=T. |last3=Reischütz |first3=P.L. |last4=Horsák |first4=M. |last5=Breugelmans |first5=K. |last6=Jordaens |first6=K. |title=Arion alpinus Pollonera, 1887 in the Czech Republic (Gastropoda: Arionidae) |journal=Malacologica Bohemoslovaca |date=2006 |volume=5 |pages=51–55|doi=10.5817/MaB2006-5-51 |doi-access=free }} but it is not developed in juveniles.{{cite journal |last1=De Wilde |first1=J.J.A. |title=Notes on the Arion hortensis complex in Belgium (Mollusca, Pulmonata: Arionidae) |journal={{lang|fr|Annales de la Société royale zoologique de Belgique|italic=unset|nocat=true}} |date=1983 |volume=113 |issue=1 |pages=87–96}} The structure is involved in receiving the partner's spermatophore.

Arion distinctus occurs in a variety of moist habitats, including gardens, waste ground and woodland, but may be absent in harsh upland habitats.{{cite book |last1=Kerney |first1=M.P. |title=Atlas of Land and Freshwater Molluscs of Britain and Ireland |date=1999 |publisher=Harley Books |location=Harley Books |isbn=9780946589487}} In Switzerland it occurs up to 2000 m.{{cite book |last1=Boschi |first1=C. |title=Die Schneckenfauna der Schweiz: ein umfassendes Bild- und Bestimmungsbuch |date=2011 |publisher=Haupt Verlag |location=Bern |isbn=9783258076973}} It is typically found amongst ground litter or sheltering under wood, stones and soil clods. Studies in agriculture and horticulture have often not distinguished A. distinctus and A. hortensis, but both species are considered to be economically significant pests.{{cite journal |last1=Glen |first1=D.M. |last2=Milsom |first2=N.F. |last3=Wiltshire |first3=C.W. |title=Effects of seed‐bed conditions on slug numbers and damage to winter wheat in a clay soil |journal=Annals of Applied Biology |date=1989 |volume=115 |issue=1 |pages=177–190 |doi=10.1111/j.1744-7348.1989.tb06825.x}}{{cite book |editor1-last=Allen-Stevens |editor1-first=T. |title=Slug control, a grower's guide |date=July 2018 |publisher=Crop Production Magazine |url=http://www.cpm-magazine.co.uk/wp-content/uploads/2018/06/Slug-Control-2018.pdf}}

This species is believed native to Western, Northern and Central Europe, but has spread eastwards, particularly in synanthropic habitats. The Andorran occurrences are the only confirmed records from the Iberian Peninsula.

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• Andorra{{cite book |last1=Borredà |first1=V. |last2=Martínez-Ortí |first2=A. |last3=Nicolau |first3=J. |title=Guia de camp dels Molluscs d'Andorra |date=2010 |publisher=Centre d'Estudis de la Neu i de la Muntanya de l'Institut d'Estudis Andorrans |location=Sant Julià de la Lòria, Andorra |isbn=978-99920-2-055-5}}
• Austria{{cite journal |last1=Reischütz |first1=P.L. |title=Die Verbreitung der Nacktschnecken Österreichs (Arionidae, Milacidae, Limacidae, Agriolimacidae, Boettgerillidae) (Supplement 2 des Catalogus Faunae Austriae) |journal={{lang|de|Sitzungsberichte, Österreichische Akademie der Wissenschaften, mathematisch-naturwissenschaftliche Klasse, Abteilung I|italic=unset|nocat=true}} |date=1986 |volume=195 |issue=5 |pages=67–190 |url=https://www.zobodat.at/pdf/SBAWW_195_0067-0190.pdf}}
• Belgium{{cite journal |last1=De Wilde |first1=J.J. |title=Further notes on the species of the Arion hortensis complex in Belgium (Mollusca, Pulmonata: Arionidae) |journal={{lang|fr|Annales de la Société royale zoologique de Belgique|italic=unset|nocat=true}} |date=1986 |volume=116 |issue=1 |pages=71–74}}
• Bulgaria
• Croatia{{cite journal |last1=Wiktor |first1=A. |title=The slugs of the former Yugoslavia (Gastropoda terrestria nuda--Arionidae, Milacidae, Limacidae, Agriolimacidae) |journal=Annales Zoologici |date=1996 |volume=46 |pages=1–110}}
• Czech Republic{{cite book |last1=Horsáak |first1=M. |last2=Juřičková |first2=L. |last3=Picka |first3=J. |title=Molluscs of the Czech and Slovak Republics |date=2013 |publisher=Kabourek |location=Zlín |isbn=978-80-86447-15-5}}
• Denmark{{cite journal |last1=Backeljau |first1=T. |last2=De Bruyn |first2=L. |title=Notes on Arion hortensis s.l. and Arion fasciatus s.l. in Denmark (Gastropoda: Pulmonata) |journal=Apex |date=1988 |volume=4 |issue=3 |pages=41–48}}
• Faroe Islands{{cite journal |last1=Solhøy |first1=T. |title=Terrestrial invertebrates of the Faroe Islands: IV. Slugs and snails (Gastropoda): Checklist, distribution, and habitats |journal=Fauna Norv. Ser. A |date=1981 |volume=2 |pages=14–27}}
• Finland{{cite book |last1=Koivunen |first1=A. |last2=Malinen |first2=P. |last3=Ormio |first3=H. |last4=Terhivuo |first4=J. |last5=Valovirta |first5=I. |title=Suomen kotilot ja etanat: opas maanilviästen maailmaan |date=2014 |publisher=Hyönteistarvike Tibale Oy |location=Helsinki |isbn=978-952-67544-6-8}}
• France
• Germany[https://www.mollbase.de/list/deunam.htm Deutsche Namen für einheimische Schnecken und Muscheln]
• Great Britain
• Hungary
• Iceland
• Ireland
• Italy (north only){{cite book |last1=Manganelli |first1=G. |last2=Bodon |first2=M. |last3=Favilli |first3=L. |last4=Giusti |first4=F. |editor1-last=Minelli |editor1-first=A. |editor2-last=Ruffo |editor2-first=S. |editor3-last=La Posta |editor3-first=S. |title=Checklist delle specie della fauna italiana |date=1995 |publisher=Calderini |location=Bologna |pages=1–60 |chapter=16. Gastropoda Pulmonata}}
• Latvia{{cite journal |last1=Greke |first1=C. |title=Die Arionidae (Gastropoda: Pulmonata) Lettlands |journal={{lang|de|Nachrichtenblatt der Ersten Vorarlberger Malakologischen Gesellschaft|italic=unset|nocat=true}} |date=1999 |volume=7 |pages=6–8|url=https://www.zobodat.at/pdf/NachErstMalaGes_7_0006-0008.pdf}}
• Lithuania{{cite journal |last1=Skujienė |first1=G. |title=Arion distinctus Mabille, 1868 (Gastropoda: Pilmonata: Arionidae) in Lithuania |journal=Acta Zoologica Lituanica |date=2004 |volume=14 |issue=2 |pages=71–76 |doi=10.1080/13921657.2004.10512582}}
• The Netherlands
• Norway (up to 69.6°N){{cite journal |last1=Backeljau |first1=T. |last2=De Meyer |first2=M. |last3=Janssens |first3=L. |last4=Proesmans |first4=R. |title=Some interesting records of land molluscs in northern Norway |journal={{lang|no|Fauna norvegica. Serie A|italic=unset|nocat=true}} |date=1983 |volume=4 |pages=7–10}}
• Poland{{cite book |last1=Wiktor |first1=A |title=Ślimaki lądowe Polski |date=2004 |publisher=Mantis |location=Olsztyn |isbn=978-83-918125-1-8}}
• Russia (Moscow){{cite journal |last1=Tappert |first1=A. |title=Die Molluskenfauna von Moskau und Moskauer Oblast, Russland |journal=Schriften zur Malakozooogie |date=2009 |volume=24 |pages=5–62}}
• Serbia
• Slovakia
• Slovenia{{cite journal |last1=Vaupotič |first1=M. |last2=Velkovrh |first2=F. |title=Slugs (Gastropoda: Pulmonata: Milacidae, Limacidae, Boettgerillidae, Agriolimacidae, Arionidae) of Slovenia |journal=Acta Biologica Slovenica |date=1 December 2002 |volume=45 |issue=2 |pages=35–52 |doi=10.14720/abs.45.2.16630|doi-access=free }}
• Sweden (below 61° N){{cite web |last1=von Proschwitz |first1=T. |title=Arion distinctus: Trädgårdssnigel |url=https://artfakta.artdatabanken.se/taxon/106672 |website=Artfakta |publisher=SLU |accessdate=19 September 2018}}
• Switzerland
• Ukraine{{cite journal |last1=Gural-Sverlova |first1=N.V. |last2=Gural |first2=R.I. |title=New findings of the slugs Arion distinctus and Arion circumscriptus (Arionidae) in the territory of Ukraine [in Russian] |journal=Ruthenica |date=2016 |volume=26 |issue=1 |pages=17–23 |url=https://biotaxa.org/Ruthenica/article/view/20102}}

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File:Arion-distinctus-map-eur-nm-moll.jpg

Arion distinctus has also been introduced beyond Europe. The following include only records in which A. distinctus has explicitly been distinguished from A. hortensis.

• Azores{{cite book |last1=Cunha |first1=R. |last2=Rodrigues |first2=P. |last3=Martins |first3=A. Frias |chapter=List of molluscs (Mollusca) |editor1-last=Borges |editor1-first=P.A.V. |display-editors=etal|title=A list of the terrestrial and marine biota from the Azores |date=2010 |publisher=Princípia |location=Cascais |pages=165–177|isbn=978-989-8131-75-1}}
• Madeira{{cite book |last1=Seddon |first1=M.B. |title=BIOTIR2: the landsnails of Madeira |date=2008 |publisher=Amgeddfa Cymru—National Museum Wales |location=Cardiff |isbn=978-0-7200-0585-1}}
• South Africa (probable identification){{cite book |last1=Herbert |first1=D.G. |title=The introduced terrestrial Mollusca of South Africa |date=2010 |publisher=South African Biodiversity Institute |location=Pretoria |isbn=978-1-919976-56-3}}
• Canada (British Columbia, Ontario, Nova Scotia){{cite book |last1=Grimm |first1=F.W. |last2=Forsyth |first2=R.G. |last3=Schueler |first3=F.W. |last4=Karstad |first4=A. |title=Identifying land snails and slugs in Canada: introduced species and native genera |date=2009 |publisher=Canadian Food Inspection Agency |isbn=978-1-100-12439-1}}
• USA (California,{{cite book |last1=Mc Donnell |first1=R.J. |last2=Paine |first2=T.D. |last3=Gormally |first3=M.J. |title=Slugs: a guide to the invasive and native fauna of California |date=2009 |publisher=University of California |isbn=978-1-60107-564-2 |url=https://anrcatalog.ucanr.edu/pdf/8336.pdf}} Pennsylvania,{{cite journal |last1=Pearce |first1=T.A. |last2=Bayne |first2=E.G. |title=Arion hortensis Férussac, 1819, species complex in Delaware and Pennsylvania, eastern USA (Gastropoda: Arionidae) |journal=Veliger |date=2003 |volume=46 |issue=4 |pages=362–363}} Hawai'i{{cite web |last1=Mc Donnell |first1=R. |last2=Richart |first2=C. |title=Surveying for Oregonian slugs in Hawai’i with the goal of removing their quarantine status |url=https://www.realchristmastreeboard.org/wp-content/uploads/2024/10/19-05-OSU-Final-Report.pdf |publisher=Real Christmas Tree Board |access-date=10 May 2025 |date=2024}})
• Taiwan{{cite journal |last1=Tsai |first1=C.-L. |last2=Wu |first2=S.-K. |title=A new Meghimatium slug (Pulmonata: Philomycidae) from Taiwan |journal=Zoological Studies |date=2008 |volume=47 |issue=6 |pages=759–766 |url=http://zoolstud.sinica.edu.tw/Journals/47.6/759.pdf |access-date=2010-09-15 |archive-date=2020-11-28 |archive-url=https://web.archive.org/web/20201128074156/http://zoolstud.sinica.edu.tw/Journals/47.6/759.pdf |url-status=dead }}
• New Zealand

Unfortunately with most relevant studies it is unclear to what extent the authors were dealing with populations of the sibling species A. hortensis or with mixed populations. However, a more recent study of a pure A. distinctus population in southern England reports results comparable with most others{{cite journal |last1=Hutchinson |first1=J.M.C. |last2=Reise |first2=H. |last3=Skujienė |first3=G |title=Life cycles and adult sizes of five co-occurring species of Arion slugs. |journal=Journal of Molluscan Studies |date=2017 |volume=83 |pages=88–105 |doi=10.1093/mollus/eyw042|doi-access=free }} (but not with Hunter 1968,{{cite journal |last1=Hunter |first1=P.J. |title=Studies of slugs of arable ground II. Life cycles |journal=Malacologia |date=1968 |volume=6 |pages=379–389}} so that study might have concerned A. hortensis). The majority of individuals matured in early winter and adults persisted until summer. Eggs laid at the beginning of this period produced animals of adult size already by the start of summer, but these disappeared underground over summer and did not mature reproductively until the end of the year. This is an annual life cycle. The development of slugs hatching from eggs laid later in spring appeared to be delayed by the dry summer conditions, generating a bimodal size distribution in autumn, and these slugs only matured in spring, with possibly some delaying further. Hence, most studies have reported a full range of sizes of this species throughout the year, although reproducing adults are largely absent over summer and autumn. Arion distinctus matures several weeks or more later than the sibling species A. hortensis. In captivity eggs took about 27 days to hatch at 12–15 °C.

Genetic evidence implies that A. distinctus is at least predominantly an outbreeder.{{cite journal |last1=Foltz |first1=D.W. |last2=Ochman |first2=H. |last3=Jones |first3=J.S. |last4=Evangeli |first4=S.M. |last5=Selander |first5=R.K. |title=Genetic population structure and breeding systems in arionid slugs (Mollusca: Pulmonata) |journal=Biological Journal of the Linnean Society |date=1982 |volume=17 |issue=3 |pages=225–241 |doi=10.1111/j.1095-8312.1982.tb02018.x}} In captivity it only produced offspring when it had had the company of a conspecific. The two oviduct morphs of A. distinctus mate with each other freely, even though only the tripartite form is able to evert its oviduct over the back of the partner. Coitus lasts 20–30 min, considerably shorter than in A. hortensis. Arion distinctus has been observed mating with A. hortensis in the wild, but no hybrids have been observed.

{{Reflist}}

{{commons category|Arion distinctus}}

• [http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/species?id=2540 Arion distinctus] at Animalbase: taxonomy, short description, distribution, biology,status (threats), images
• [http://eol.org/pages/455164/media Arion distinctus] images at the Encyclopedia of Life

{{Taxonbar|from=Q1405900}}

Category:Arion (gastropod)

Category:Gastropods described in 1868

Category:Taxa named by Jules François Mabille