Clytia hemisphaerica is a hydrozoan of the Campanulariidae family. This species was chosen some years ago as a promising model for molecular and cellular studies in development and evolution thanks to its phylogenetic position, the ease of culturing all life cycle stages under laboratory condition and its accessibility to different experimental techniques. Furthermore, this tiny jellyfish represents an important potential contribution to the understanding of fundamental scientific questions about animal complexity possessing significant features such as a complex nervous system, sensory organs and striated muscle which characterize the medusa form.
Clytia hemisphaerica has a typical hydrozoan life cycle: the free-swimming medusa is the sexual form and can grow up to 1 cm in diameter. Fertilization is external and follows the simultaneous release of gametes from males and females medusae. The fertilized eggs develop into “planula” larvae which swim directionally thanks to ectodermal cilia. Around three days after the fertilization the planula is ready to undergo metamorphosis and to give rise to a primary feeding polyp. The polyp propagates on the sea bed forming a colony within two polyp types coexist: the gonozooid, specialized for medusa budding and the feeding form, gastrozooid. Newly released baby medusa reach maturity after 2-3 weeks and the entire life cycle can be completed in a minimum of 6-8 weeks.
E. Houliston, T.Momose and M.Manuel (2010). Clytia hemisphaerica: a jellyfish cousin joins the laboratory. Trends Genetics