Start here: Slug or Snail?
Parts of a slug
Common slug identification key
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.
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.