American lab returned single snail (7)
'snail' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'american lab returned single' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'returned' says the letters should be written in reverse.
'single' becomes 'one' (similar in meaning).
'lab' back-to-front is 'bal'.
Can you help me to learn more?
(Other definitions for abalone that I've seen before include "sea mollusc", "Ear-shaped shell", "Mollusc with an oval shell lined with bluish mother-of-pearl", "Mollusc, the sea-ear", "Edible shellfish, sea-ear".)