Gastropod for sailor marooned? (7)
I believe the answer is:
abalone
'gastropod' is the definition.
(abalone is a kind of gastropod)
'sailor marooned?' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'marooned?' becomes 'alone' ('alone' can be similar in meaning to 'marooned').
'ab'+'alone'='ABALONE'
'for' acts as a link.
(Other definitions for abalone that I've seen before include "marine creature" , "Mollusc, the sea-ear" , "Seafood" , "Mollusc also called ormer" , "Would you be able on a US shellfish?" .)