Lead search for marine creature (8)
I believe the answer is:
starfish
'marine creature' is the definition.
(I know that starfish is a type of marine creature)
'lead search' is the wordplay.
'lead' becomes 'star' (synonyms).
'search' becomes 'fish' (fishing is a kind of searching).
'star'+'fish'='STARFISH'
'for' is the link.
(Other definitions for starfish that I've seen before include "Heavenly marine animal?" , "Asteroid (in the sea)" , "Astral aquatic animal" , "Has rifts (anag)" , "Rock pool creature with five arms" .)