Garden molluscs » Slug or snail? » Garden slugs » Position of pneumostome » Behind the mid-line of mantle
The British slugs which have the pneumostome situated behind the mid-point of the mantle belong to one of two families: the family Milacidae or the family Limacidae.
The Milacidae have a small symmmetrical internal shell, and have a "keel" on the back which runs from the tip of the tail right up to the mantle, as on the specimen to the right…
…whilst the Limacidae have a small asymmetrical internal shell, and the "keel" runs from the tip of the tail to only partway up the back, as on the specimen to the left.
Click on the image above which shows features similar to your specimen