Landed gentleman bears right, then left, finding arboreal animal (8)
I believe the answer is:
squirrel
'arboreal animal' is the definition.
'landed gentleman bears right then left' is the wordplay.
'landed gentleman' becomes 'squire'.
'bears' indicates putting letters inside (some letters carry or bear others).
'right' becomes 'r' (common abbreviation).
'then' says to put letters next to each other.
'left' becomes 'l' (common abbreviation).
'squire' placed around 'r' is 'squirre'.
'squirre'+'l'='SQUIRREL'
'finding' acts as a link.
(Other definitions for squirrel that I've seen before include "Arboreal rodent with long bushy tail" , "Grey or (rarely) red woodland creature" , "Brown or red rodent" , "hide away" , "Bushy-tailed rodent" .)