Legendary ruler giving away universal ring case for scarab, say (9)
I believe the answer is:
arthropod
'scarab say' is the definition.
(scarab is a kind of arthropod)
'legendary ruler giving away universal ring case' is the wordplay.
'legendary ruler' becomes 'arthur' (King Arthur).
'giving away' suggests deleting specific letters.
'universal' becomes 'u'.
'ring' becomes 'o'.
'case' becomes 'pod' (pod is a kind of case).
'arthur' with 'u' taken out is 'arthr'.
'arthr'+'o'+'pod'='ARTHROPOD'
'for' is the link.
(Other definitions for arthropod that I've seen before include "Invertebrate" , "Creature such as insect or crustacean" , "spider, for example" , "worker, perhaps" , "One has external skeleton" .)