Creature a tailless sort — positive about that? (8)
I believe the answer is:
platypus
'creature' is the definition.
(platypus is a kind of creature)
'a tailless sort positive about that?' is the wordplay.
'tailless' means to remove the last letter (the tail of the word is removed).
'sort' becomes 'type' (type is a kind of sort).
'positive' becomes 'plus' (similar in meaning).
'about that?' means one lot of letters goes inside another.
'type' with its last letter taken away is 'typ'.
'a'+'typ'='atyp'
'atyp' placed within 'plus' is 'PLATYPUS'.
(Other definitions for platypus that I've seen before include "Aussie creature" , "Australian mammal with large bill and webbed feet" , "Australian egg-producer" , "Aquatic creature" , "Primitive mammal, duck-billed" .)