Relative mRNA expression of Clock Genes in Nematostella vectensis. Data of a) Clock, b) Cycle, c) Timeout, d) Cry1a, e) Cry1b and f) Cry2 in Nematostella vectensis kept in a light–dark (12:12 h), constant darkness, or constant darkness with melatonin supplementation (0.1 μM). Data normalized by the ribosomal protein P0. Each point represents five individuals. *Statistically different from light–dark with P <0.05.