Lemur behind riverside houses (5)
I believe the answer is:
indri
'lemur' is the definition.
(indri is a kind of lemur)
'behind riverside houses' is the wordplay.
'houses' says the answer is hidden in the clue (part of the clue houses the answer).
'INDRI' is hidden within 'behind riverside'.
(Other definitions for indri that I've seen before include "Animal" , "Big Madagascan lemur" , "native of Madagascar" , "Short-tailed lemur of Madagascar" , "large primate" .)