Small freshwater turtle (8)
I believe the answer is:
terrapin
'small freshwater turtle' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for terrapin that I've seen before include "Chelonian reptile" , "Hardback" , "Partner I found for freshwater tortoise" , "Little turtle" , "A reptile; a printer (anag.)" .)