Start here: Slug or Snail? 

Slugs have: 

• no visible shell or a small shell that cannot contain their body.

Continue to slugs

Snails have:

• a coiled shell that can contain most or all of their body.

Continue to snails

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Slugs

Parts of a slug

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Common slug identification key

With visible shell

Without visible shell
1. Pneumostome in anterior half of mantle

2. Pneumostome in middle or posterior half of mantle.

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Slugs with anterior pneumostomes

1. No line where tail can be shed. Caudal pore present. Body tubercles uneven, ovoid in shape with no apparent pattern. 

Arion, roundback slugs

2. ​Line where tail can be shed (can be difficult to see). This can be an impressed line or indicated by a change in the skin texture. No caudal pore. Body tubercles typically diamond shaped in diagonal rows. 

Prophysaon, tail droppers