Oocyte maturation is a crucial feature of animal biology and is tightly regulated to optimise reproductive success. However, the nature of the maturation-inducing hormones (MIHs) that trigger this process is unclear and, to date, only a few such MIHs have been identified. Here, Noriyo Takeda and colleagues identify and characterise neuropeptides that act directly as MIHs in jellyfish (dev156786). Using two species of jellyfish, Clytia hemisphaerica and Cladonema pacificum, which are induced to spawn by dark-light and light-dark transitions, respectively, the authors first show that MIH activity is produced by isolated jellyfish gonads in response to light transitions, in particular by gonad ectoderm tissue. Using transcriptomic analyses, the researchers identify short amidated neuropeptides that are expressed preferentially in the gonad ectoderm. They further show that these peptides can induce oocyte maturation, while specific antibodies against them can neutralise native MIH activity. Finally, they show that the peptides are produced by neurosecretory cells in the gonad ectoderm of female and male jellyfish, and can trigger both egg and sperm release, suggesting that they act to coordinate spawning. Together, these findings reveal that amidated neuropeptides act as bona fide MIHs in jellyfish and provide clues into the evolution of neuroendocrine-mediated regulation of reproduction.