Transport two horses, astride black animal (8)
I believe the answer is:
bushbaby
'animal' is the definition.
(I've seen this before)
'transport two horses astride black' is the wordplay.
'two horses' can mean two substitutions for 'horse'.
'transport' becomes 'bus' (busing is a kind of transporting).
'horse' becomes 'H' (synonyms).
'horse' becomes 'bay' (bay is a kind of horse).
'astride' indicates putting letters inside.
'black' becomes 'b' (as in pencil classifications).
'bay' going around 'b' is 'baby'.
'bus'+'h'+'baby'='BUSHBABY'
(Other definitions for bushbaby that I've seen before include "Small, nocturnal, tree-dwelling primate of Africa with large eyes" , "Big-eyed, long-tailed African primate" , "Nocturnal African lemur (closely related to one of two US presidents?)" , "Small African nocturnal primate with large eyes" , "Small African lemur, like shrubbery infant" .)