Invertebrate (9)
I believe the answer is:
earthworm
'invertebrate' is the definition.
(earthworm is a kind of invertebrate)
This is all the clue.
(Other definitions for earthworm that I've seen before include "What mole eats" , "Burrowing creature" , "Soil-dwelling invertebrate" , "One burrows" , "Creature that burrows in soil" .)