Unexpected diversity of bioluminescence in planktonic worms

The vast majority of pelagic bioluminescent organisms emit a blue light with emission maxima (λ_max ) ranging from 450 to 490 nm. Among the known outliers, the tomopterids (Annelida: Polychaeta) are usually described as yellow-emitters (λ_max  = 565-570 nm) for which bioluminescence functions as a specific recognition signal. Here, we report the first data regarding the colours emitted by four different tomopterid species, Tomopteris pacifica, T. carpenteri, T. septentrionalis and T. planktonis. Surprisingly, T. planktonis is a blue-emitter (λ_max  = 450 nm). Our pharmacological results on T. planktonis support cholinergic control, as recently demonstrated in the yellow-emitter, T. helgolandica. Moreover, as revealed by epifluorescence microscopy, the light seems to be produced in both species from the same yellow-pigmented parapodial glands. Despite these similarities, tomopterids express an unexpected diversity of bioluminescent colour patterns. This leads us to reassess the ecological value of bioluminescence within this group.