List includes a respiratory organ set back in a reptile (9)
I believe the answer is:
alligator
'a reptile' is the definition.
(alligator is a kind of reptile)
'list includes a respiratory organ set back' is the wordplay.
'list' becomes 'rota' (rota is a kind of list**).
'includes' means one lot of letters goes inside another.
'respiratory organ' becomes 'gill' (gill is a kind of respiratory organ).
'set back' says the letters should be written in reverse.
'a'+'gill'='agill'
'rota' placed around 'agill' is 'rotagilla'.
'rotagilla' in reverse letter order is 'ALLIGATOR'.
'in' is the link.
(Other definitions for alligator that I've seen before include "that is scaled" , "Cold-blooded killer, maybe" , "predator" , "Reptile like a crocodile" , "Predatory cold-blooded killer" .)