It lives in wet, tree-lined places (3)
I believe the answer is:
eel
'it lives' is the definition.
The definition suggests a singular noun which matches the answer.
'wet tree-lined places' is the wordplay.
'EEL' is hidden within the letters.
But, I am not sure how this is indicated.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for eel that I've seen before include "Creature like conger or moray" , "Moray or electric, for instance" , "Slippery type" , "Slender fish" , "A sea snake" .)