Animal impression (4)
I believe the answer is:
seal
This clue is a double definition.
'animal' is the first definition.
(I have seen 'Marine animal' mean 'seal' so perhaps 'animal' could also mean 'seal')
'impression' is the second definition.
(I know that seal is a type of impression)
(Other definitions for seal that I've seen before include "Aquatic mammal - close securely" , "See 7" , "Wax stamp" , "Make airtight" , "Amphibious mammal or stamp of authenticity" .)