[Hydromedusae] One of the most important and characteristic features of Hydrozoan development. In the morphogenesis of medusa buds, of fixed gonophores or of eumedusoids, an invagination of the ectoderm of the apical budding zone produces a solid multistratified nodule, the entocodon, which subsequently develops a cavity: the future subumbrellar cavity. As a general rule the entocodon gives rise to ectodermal components only (the manubrial ectoderm; the subumbrellar ectoderm and the internal layer of the velum and their striated muscles); the endodermal components of the buds (manubrium, gastro-vascular canals) being formed by an evagination of the "mother" endoderm (spadix).

Alternative forms for Entocodon : Glockenkern, Medusary nodule.