Violet-emitting Polycirrus sp. ISK (Polychaeta: Terebellidae) from Sea of Japan

The worm belonging to Terebellidae usually lives in a small hole or crack in a rock under coastal Sea area. The worm exhibits characteristic morphology with a large number of tentacles stretching out of the body part embedded in the rock to collect detritus and various small zooplanktons. Luminous species from Terebeliidae has been described since the 19th Century including the genus Polycirrus. Luminous Polycirrus spp. are widespread over the world despite the light emission modes are different. This genus includes species emit violet light, which is the shortest wavelength range of known luminous animals. However, molecular basis for these worms are lacking and light emission mechanism is remaining to be enigmatic. In the present study, we collected violet-emitting Polycirrus sp. ISK in Japan and performed RNA-Seq analysis separately for the tentacle and body part from a single specimen. Although we were unable to identify light emission molecules either enzyme nor substrate, we found that some genes probably involved in the innate immunity specifically expressed in the tentacle part. Also, cytochrome oxidase I gene sequence obtained by RNA-Seq analysis enabled us to perform molecular phylogenetic analysis to confirm this worm belonging to the genus polycirrus.