Five-armed sea creature (8)
I believe the answer is:
starfish
'five-armed sea creature' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for starfish that I've seen before include "Asteroid (in the sea)" , "Marine creature with five arms" , "Astral aquatic animal" , "One found at sea" , "Sea creature with five arms coming from central disk" .)