Animal raced round it? So unlikely (8)
I believe the answer is:
tortoise
'animal' is the definition.
(I've seen this before)
'raced round it? so unlikely' is the wordplay.
'raced' becomes 'tore' (tearing is a kind of racing).
'round' means one lot of letters goes inside another.
'unlikely' is an anagram indicator.
'it'+'so'='itso'
'itso' anagrammed gives 'tois'.
'tore' enclosing 'tois' is 'TORTOISE'.
(Other definitions for tortoise that I've seen before include "Slow-moving reptile that won race against a hare" , "Tie roots (anag)" , "Shelled reptile" , "Lettuce-munching plodder" , "Land turtle" .)