Invertebrate rook oddly found in new hardtop (9)
I believe the answer is:
arthropod
'invertebrate' is the definition.
(arthropod is a kind of invertebrate)
'rook oddly found in new hardtop' is the wordplay.
'oddly' means one should take alternating letters.
'found in' means one lot of letters goes inside another.
'new' indicates an anagram.
The alternating letters of 'rook' are 'ro'.
'hardtop' anagrammed gives 'arthpod'.
'ro' put within 'arthpod' is 'ARTHROPOD'.
(Other definitions for arthropod that I've seen before include "Invertebrate" , "One has external skeleton" , "Such as a crustacean or spider" , "Creature such as insect or crustacean" , "worker, perhaps" .)