Remarks: (1) The illustration of the parapodium in the original description of O. platykephale (BLAKE 1985: Fig. 14C) was shown upside down and misinterpreted. This error was later noted by BLAKE & HILBIG (1990) and corrected by SOLÍSWEISS & HILBIG (1992). The original figure has been corrected here. (2) A closely related morphotype of O. platykephale is present in the same samples from the Guaymas basin hydrothermal mounds. It differs externally from O. platykephale having a peristomium with two achaetous rings and a globose dorsal cirrus (see Fig. 2-6). Its mandibles differ also from O. platykephale being more spindly and curved. Its specific status remains to be discussed (likely morphological variants or different stages of O. platykephale).