Two new symbiotic species of Hesionidae, Oxydromus cemacs sp. nov. and Podarkeopsis balanoglossi sp. nov., are described from the West Pacific, expanding our understanding of symbiotic diversity among polychaetes. Oxydromus cemacs sp. nov. was collected in Malaysian shallow waters in association with the sea urchin Temnopleurus toreumaticus and is distinguished by its unique dorsal pigmentation showing white transverse bands lacking central spots. Podarkeopsis balanoglossi sp. nov., found in the burrows of the acorn worm Balanoglossus carnosus in Japan, is characterized by ten papillae on the proboscis margin and serrated notochaetae from segment 10 onwards, which are absent on segments 5–9. Notably, this represents the ninth polychaete species reported in association with an acorn worm, the third such case within Hesionidae (the first outside the genus Oxydromus ), the first known symbiotic species within Podarkeopsis , and the second report for the genus in the Indo-Pacific. These findings shed light on the diverse evolutionary pathways of symbiotic relationships in polychaetes and underscore the targeted sampling value in uncovering cryptic symbiotic taxa.
Jimi et al. (Wed,) studied this question.