Salty pup, mixed-up creature (8)
I believe the answer is:
platypus
'creature' is the definition.
(platypus is a kind of animal)
'salty pup mixed-up' is the wordplay.
'mixed up' indicates an anagram.
'salty'+'pup'='saltypup'
'saltypup' with letters rearranged gives 'PLATYPUS'.
(Other definitions for platypus that I've seen before include "Australian resident" , "Aussie creature" , "Unusual Australian" , "Australian mammal with large bill and webbed feet" , "Australian mammal with duckbill" .)