Playful marine mammal (5)
I believe the answer is:
otter
'playful marine mammal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for otter that I've seen before include "Something furry" , "fish-eater displayed" , "furry creature" , "river in Honiton" , "Mammal, 'Tarka'" .)