Ape on another planet — second to feature in picture (8)
I believe the answer is:
marmoset
'ape' is the definition.
(thesaurus)
'another planet second to feature in picture' is the wordplay.
I cannot really see how this works, but
'another' could be 'r' (I've seen this in other clues) and 'r' is found within the answer.
'second' could be 'mo' (both are short periods of time) and 'mo' is located in the answer.
This explanation may well be incorrect...
'on' acts as a link.
Can you help me to learn more?
(Other definitions for marmoset that I've seen before include "Primate" , "Somme rat? (anag)" , "Arms me to (anag) - animal" , "Turn morse mat over for the monkey" , "Little monkey" .)