How do i distinguish different members of the Arion genus

Nature Talk
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Im fascinated by the slugs from genus Arion and want to be able to identify them as accurately as possible. Im not just talking about the most popular species, i mean every single one if possible

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Welcome to the forum! Like many terrestrial gastropods, differentiating Arion spp. typically requires dissection. It’s probable that some species are only found in certain regions, but if you want to be sure, you will need to dissect them. This is especially true where they have been introduced, as typically they can only be IDed to subgenus externally. This page is a helpful starting point for learning dissections and differentiating many introduced species, but if you want to know how to ID all of them you will likely need to search the primary literature. You may also be interested in observations from this project:

https://www.inaturalist.org/projects/terrestrial-gastropod-dissections

Someone more familiar with the European fauna may be able to provide more advice.

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That makes sense. I don’t like killing animals unless necessary, but thank you for the links, i think those will come handy in the future.

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Other features such back color, foot color, mucus color, and shape when contracted are also helpful. But to be absolutely sure, dissection and DNA are best.

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Every single one would probably need DNA analysis for the immatures. And if you mean every single species worldwide, then that is a very big task. You would need a decade or so of experience and lots of discussion with other Arion taxonomists. Where are you based? This is good for Britain and Ireland:

Slugs of Britain and Ireland Identification, Understanding and Control

Field / Identification Guide Identification Key

Series: Field Studies Council AIDGAP Guides Volume: OP160

By: Ben Rowson(Author), James Turner(Author), Roy Anderson(Author), Bill Symondson(Author)

136 pages, colour photos, colour illustrations, colour distribution maps

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I’m based in Poland and often travel throughout central and eastern Europe, thats the region i want to focus on

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Im specifically talking about Arion hortensis, Arion fasciatus, Arion distinctus, Arion fuscus, Arion intermedius and the young of Arion vulgaris and Arion ater. Ive been having trouble with identifying some of these for a while. I also dont euthanise the animals, so dissection and dna analysis won’t work.

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Sounds like you are continuing this thread:

https://forum.inaturalist.org/t/how-do-i-distinguish-different-members-of-the-arion-genus/75914

Things like foot color, skirt color, mantle color, and mucus color can help distinguish subgenera. I don’t think there are reliable ways to distinguish species within the same subgenus without dissection or DNA. There may be for certain areas (A. intermedius I think has a distinct shape when contracted), but in my experience it’s not really possible. You can try using this interactive key:

https://idtools.org/mollusk/index.cfm?pageID=3376

This one is also helpful:

https://www.carnegiemnh.org/science/mollusks/pa_key.html

And this one:

https://anrcatalog.ucanr.edu/pdf/8336.pdf

I have heard there is a good book on British land snails/slugs that might be more helpful for European fauna, but I don’t remember which one. The species you mention are invasive lots of places so there are a decent number of sources.

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I moved the above two posts to this thread to keep all the discussion in one place.

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