Scyphozoan jellyfish, or scyphomedusae, are conspicuous members of many ocean ecosystems, and have large impacts on human health and industry. Most scyphomedusae are the final stage in a complex life cycle that also includes two intermediate stages: the larval planula and benthic polyp. In species with all three life‐cycle stages, the metamorphosis of a polyp into a juvenile scyphomedusa (ephyra) is termed strobilation, and polyps can produce one ephyra (termed monodisc strobilation) or many ephyrae (termed polydisc strobilation). In contrast to species with planula, polyp and medusa stages, a handful of scyphozoan species possess modified life cycles with reduced or absent stages. The evolutionary patterns associated with strobilation and life‐cycle type have not been thoroughly investigated, and many studies of ephyra development and strobilation induction are not yet synthesized. Herein, I place the development of scyphomedusae in an evolutionary context. I first review the current evolutionary hypotheses for Scyphozoa. Next, I review what is known about scyphomedusa development across a broad diversity of species, including the first signs of strobilation, the formation of strobila segments, and the morphogenesis of ephyrae. I then review cases where the canonical scyphozoan life cycle has been modified, and take advantage of phylogenetic hypotheses to place these observations in an evolutionary context. I show that the evolution of monodisc strobilation occurred at least twice, and that the loss of intermediate life‐cycle stages occurred several times independently; by contrast, the reduction of the medusa stage appears to have occurred within a single clade. I then briefly review the major natural cues of strobilation induction. Finally, I summarize what is currently known about the molecular mechanisms of strobilation induction and ephyra development. I conclude with suggestions for future directions in the field.

中文翻译：

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水母水母的进化与发育

Scyphozoan 水母，或 scyphomedusae，是许多海洋生态系统的重要成员，对人类健康和工业产生巨大影响。大多数 scyphomedusae 是复杂生命周期的最后阶段，其中还包括两个中间阶段：幼虫浮游生物和底栖息肉。在具有所有三个生命周期阶段的物种中，息肉变态为幼鱼（ephyra）称为 strobilation，息肉可以产生一个 ephyra（称为单盘 strobilation）或许多 ephyrae（称为 polydisc strobilation）。与具有浮游生物、息肉和水母阶段的物种相比，少数水生动物物种的生命周期有所改变，阶段减少或不存在。与频闪和生命周期类型相关的进化模式尚未得到彻底研究，许多关于 ephyra 发育和 strobilation 诱导的研究尚未合成。在此，我将 scyphomedusae 的发展置于进化背景中。我首先回顾了 Scyphozoa 的当前进化假设。接下来，我回顾了关于 scyphomedusa 在广泛的物种多样性中的发展，包括 strobilation 的最初迹象、strobila 节段的形成和 ephyrae 的形态发生。然后，我回顾了典型的水生动物生命周期被修改的案例，并利用系统发育假设将这些观察结果置于进化环境中。我表明，单盘 strobilation 的进化至少发生了两次，并且中间生命周期阶段的损失独立发生了几次；相比之下，美杜莎阶段的减少似乎发生在单个进化枝中。然后我简要回顾了频闪感应的主要自然线索。最后，我总结了目前已知的关于 strobilation 诱导和 ephyra 发育的分子机制。最后，我提出了对该领域未来方向的建议。