Life cycle, morphology and medusa ontogenesis of Turritopsis dohrnii (Cnidaria: Hydrozoa)

In spite of considerable research effort on the "immortal jellyfish" Turritopsis dohrnii (Weismann, 1883), a comprehensive account including the ontogenetic stages throughout its normal life cycle is still missing. Here, we report the development of the medusa morph, with description of four consecutive stages distinguished by the morphology of the umbrellar apex and the number of marginal tentacles. Medusae reared at two different temperatures (14 and 25°C) showed identical morphological features, but with shorter developmental time at higher temperature. Additional information on the morphology of the polyp stage is also provided. The implications for an easy morphological identification of T. dohrnii medusae from other congeneric species are discussed.