Poor hart sadly died as an insect, say (9)
I believe the answer is:
arthropod
'an insect say' is the definition.
(insect is a kind of arthropod)
'poor hart sadly died' is the wordplay.
'sadly' indicates anagramming the letters.
'died' becomes 'd' (abbreviation next to the year of someone's death).
'poor'+'hart'='poorhart'
'poorhart' anagrammed gives 'arthropo'.
'arthropo'+'d'='ARTHROPOD'
'as' acts as a link.
(Other definitions for arthropod that I've seen before include "worker, perhaps" , "One has external skeleton" , "Creature such as insect or crustacean" , "Such as a crustacean or spider" , "Invertebrate" .)