Beaver-like rodent (8)
'beaver-like rodent' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for coypu that I've seen before include "Large semiaquatic rodent" , "S American rodent inadvertently introduced into Europe" , "Animal -- source of nutria fur" , "Beaver-like creature" , "S. American "beaver"" .)
(Other definitions for musquash that I've seen before include "Beaver-like rodent with dark glossy brown fur" , "Type of fur" , "Aquatic rodent" , "Beaver-like rodent of North America with dark glossy fur" , "Fur of the muskrat" .)