Marine animal’s unpleasant smell pervading most of ocean (6)
I believe the answer is:
sponge
'marine animal's' is the definition.
(thesaurus)
'unpleasant smell pervading most of ocean' is the wordplay.
I cannot quite understand how this works, but
'smell' could be 'pong' (I've seen this before) and 'pong' is located in the answer.
The remaining letters 'se' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sponge that I've seen before include "Madeira, say" , "Cadge - porous object used for washing" , "mop" , "Scrounge; wiper" , "Soft, absorbent material used for washing" .)