Apes resent bats and monster (3,7)
I believe the answer is:
sea serpent
'monster' is the definition.
(sea serpent is a kind of monster)
'apes resent bats' is the wordplay.
'bats' indicates an anagram (slang for mad).
'apes'+'resent'='apesresent'
'apesresent' is an anagram of 'SEA SERPENT'.
'and' acts as a link.
(Other definitions for sea serpent that I've seen before include "Legendary creature" , "monster of the deep" .)