Web-toed mammal (5)
I believe the answer is:
otter
'web-toed 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 "river in Honiton" , "eg Tarka" , "Freshwater brown carnivore" , "Fish-eater of the weasel family" , "Semi-aquatic creature" .)