Animal in chest a pirate buried (5)
I believe the answer is:
tapir
'animal' is the definition.
(tapir is a type of animal)
'in chest a pirate buried' is the wordplay.
'in' indicates a hidden word.
'TAPIR' can be found hidden inside 'chest a pirate buried'.
(Other definitions for tapir that I've seen before include "I part with the pig-like animal" , "Ungulate" , "Long-nosed, hoofed mammal" , "Nocturnal hoofed animal" , "Animal with elongated snout" .)