Creature belonging to religious body (6)
I believe the answer is:
insect
'creature' is the definition.
(insect is a kind of creature)
'belonging to religious body' is the wordplay.
'belonging to' becomes 'in' (in can mean being a member of).
'religious body' becomes 'sect' (I've seen this in another clue).
'in'+'sect'='INSECT'
(Other definitions for insect that I've seen before include "Worthless person" , "Entangle; open fabric" , "Small arthropod creature" , "Praying mantis, say" , "Bee or beetle, for example" .)