Possible Clues:

• When on board, the primate has to obey like this
• 'I understand, sir!'
• Rare primate from thirty eight down
• Primate's main way of expressing agreement
• Yes, it's on board for one to monkey with
• Salty assent
• ... and their selfish-sounding compliance
• Nocturnal primate - agreement to obey
• Mate's reply
• Madagascan lemur-like primate