Crew, not top grade, bring in one sea creature … (5)

I believe the answer is:

squid

'one sea creature' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for squid that I've seen before include "Large cephalopod" , "Sea creature" , "Ten-armed mollusc" , "Edible eight-arm mollusc" , "Item of seafood" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app