It consists of three languages, all of which are distinguished by severe truncation of many inherited roots and the compensatory development of suprasegmentals on vowels: phonemic tone in Yabem and Bukawa (Ross 1993) and nasalization in Kela (Johnson 1994).
Ross, Malcolm (1988). Proto Oceanic and the Austronesian languages of western Melanesia. Canberra: Pacific Linguistics.
Ross, Malcolm (1993). "Tonogenesis in the North Huon Gulf chain." In Jerold A. Edmondson and Kenneth J. Gregerson, eds., Tonality in Austronesian languages, 133–153. Oceanic Linguistics Special Publication No. 24. Honolulu: University of Hawai‘i Press.