Simple life (6)
I believe the answer is:
amoeba
'simple life' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amoeba that I've seen before include "little creature" , "Simple creature" , "Microscopic, single-cell creature" , "Protozoon" , "Tiny one-celled animal in water" .)