Sea creature caught by mouth (5)
I believe the answer is:
coral
'sea creature' is the definition.
(organism that lives in the sea)
'caught by mouth' is the wordplay.
I cannot quite see how this works, but
'caught' could be 'c' (cricket abbreviation) and 'c' is located in the answer.
'by mouth' could be 'oral' (oral can mean relating to the mouth) and 'oral' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for coral that I've seen before include "Deep pink 11 across" , "Hard substance on the seabed" , "Basis of reefs" , "Pinkish-red colour" , "Hard pink substance formed by skeletons of tiny sea creatures" .)