Worm that is wrapped around in anorak (6)
I believe the answer is:
nereid
'worm' is the definition.
(I've seen this before)
'that is wrapped around in anorak' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'wrapped around' is a reversal indicator.
'in' is an insertion indicator.
'anorak' becomes 'nerd' (I've seen this before).
'ie' reversed gives 'ei'.
'ei' going within 'nerd' is 'NEREID'.
(Other definitions for nereid that I've seen before include "Mythological sea nymph" , "Sea-nymph" , "End ire (anag) - sea nymph" , "Bristle worm" , "Sea nymph in greek mythology (6)" .)