The few structural specializations in (adult lampreys) pharynx include complex valves on the external gill openings that direct the tidal flow, and the division of the ancestral pharynx into an oesophagus and a respiratory pharynx.[well established][VHOG]
DOI:10.1111/j.1096-3642.1996.tb01658.x Mallatt J, Ventilation and the origin of jawed vertebrates: a new mouth. Zoological Journal of the Linnean Society (1996)