Three new species of glow-in-dark worms discovered in shallow waters of Japan

Surprisingly, they bear a striking resemblance to some Japanese folklore characters. "We used the names of Japanese yokai, such as onibi and aoandon, for the new species because the hazy violet-blue bioluminescence emitted by the Polycirrus species is strikingly similar to the descriptions of these creatures found in folklore,” said Naoto Jimi, one of the authors of this new study, in a statement.

On the other hand, Polycirrus ikeguchii is named after Shinichiro Ikeguchi, the former director of the Notojima Aquarium.

Studying bioluminescence nature 

These newfound species belong to the class of Polychaetes marine worms. These are said to be creatures that have survived five mass extinctions and have been on the planet since the Cambrian period 505 million years ago. 

Polycirrus worms are known for their elongated tentacles that grow from their mouths. This feature allows them to find food while moving slowly through river sediment. According to the authors, these creatures are a valuable subject for studying the bioluminescence nature in animals.

There are over 7,000 luminescent organisms known worldwide, however, experts have been able to study only a small number of them in-depth. 

"Understanding these luminescence mechanisms contributes to medical and life science research. Bioluminescence is a treasure trove of interesting and unusual chemistry. We intend to use our findings to deepen our understanding of the molecular nature of this phenomenon and apply this knowledge to the development of new life sciences technologies," said Jimi. 

The results can be accessed in the journal Royal Society Open Science.

Study abstract:

Bioluminescence, a phenomenon observed widely in organisms ranging from bacteria to metazoans, has a significant impact on the behaviour and ecology of organisms. Among bioluminescent organisms, Polycirrus, which has unique emission wavelengths, has received attention, and advanced studies such as RNA-Seq have been conducted, but they are limited to a few cases. In addition, accurate species identification is difficult due to lack of taxonomic organization. In this study, we conducted comprehensive taxonomic survey of Japanese Polycirrus based on multiple specimens from different locations and described as three new species: Polycirrus onibi sp. nov., P. ikeguchii sp. nov. and P. aoandon sp. nov. The three species can be distinguished from the known species based on the following characters: (i) arrangement of mid-ventral groove, (ii) arrangement of notochaetigerous segments, (iii) type of neurochaetae uncini, and (iv) arrangement of nephridial papillae. By linking the bioluminescence phenomenon with taxonomic knowledge, we established a foundation for future bioluminescent research development. We also provide a brief phylogenetic tree based on cytochrome c oxidase subunit I (COI) sequences to discuss the evolution of bioluminescence and the direction of future research.