Duck-billed creature (8)
I believe the answer is:
platypus
'duck-billed creature' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for platypus that I've seen before include "Primitive mammal, duck-billed" , "Duck-billed creature" , "Australian mammal with large bill and webbed feet" , "One's billed in flat manner" , "river creature" .)