Eight-limbed mollusc (7)
I believe the answer is:
octopus
'eight-limbed mollusc' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for octopus that I've seen before include "Tentacled marine mollusc" , "army swimmer" , "Cops out (anag.)" , "Invertebrate sea creature with three hearts" , "person with widespread influence" .)