"The moon governs reproductive cycles in a broad range of marine animals, including cnidarians, polychaetes, crustaceans, echinoderms and fishes. Even outside the animals, lunar reproductive cycles have been described, such as in brown algae or foraminifers. Despite their fundamental nature, and decades of classical observations, close to nothing is known about the molecular processes that underly these lunar reproductive cycles.We will take advantage of the recent advance in molecular resources and tools in the bristle worm Platynereis dumerilii, which has long served as a key model for classical experimental studies on lunar periodicity. The combination of modern techniques with well-founded classical observations will allow us to decipher, for the first time, the hormonal cues that are regulated by the lunar cycle and are responsible for the orchestration of gonadal maturation and trunk regeneration.The project builds on established methodology, as well as on the first results of a successful pioneer screen and has three major aims:(1) the functional investigation of two hormones we recently identified to be under lunar cycle control.(2) the extension of our successful pioneer screen to understand to which extent other neurohormonal components change over the lunar phase.(3) the identification of the elusive inhibitory brain hormone that directly acts on the gonads to inhibit premature maturation.Together, these experiments will lead us to first significant insights into the molecular nature of the hormonal network that underlies moonlight-dependent periodicity and regeneration."