Crustacean scrabbles around (4)
I believe the answer is:
crab
'crustacean' is the definition.
(I know that crab is a type of decapod)
'scrabbles around' is the wordplay.
'around' says the answer is hidden in the clue.
'CRAB' is hidden in the letters of 'scrabbles'.
(Other definitions for crab that I've seen before include "A crustacean; type of apple" , "The constellation Cancer" , "One may be caught" , "Sideways scuttler" , "terrible row" .)