Symmetry in the arrangement of body parts is a distinctive phylogenetic feature of animals. Cnidarians show both bilateral and radial symmetries in their internal organs, such as gastric pouches and muscles. However, how different symmetries appear during the developmental process remains unknown. Here, we report intraspecific variations in the symmetric arrangement of gastric pouches, muscles, and siphonoglyphs, the Anthozoan-specific organ that drives water into the organism, in D. lineata (Diadumenidae, Actiniaria). We found that the positional arrangement of the internal organs was apparently constrained to either biradial or bilateral symmetries depending on the number of siphonoglyphs. Based on the morphological observations, a mathematical model of internal organ positioning was employed to predict the developmental backgrounds responsible for the biradial and bilateral symmetries. In the model, we assumed that the specification of gastric pouches is orchestrated by lateral inhibition and activation, which results in different symmetries depending on the number of siphonoglyphs. Thus, we propose that a common developmental program can generate either bilateral or biradial symmetries depending on the number of siphonoglyphs formed in the early developmental stages.

中文翻译：

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海葵 D. lineata 胃囊排列对称性的多态性

身体部位排列的对称性是动物独特的系统发育特征。刺胞动物的内部器官，如胃囊和肌肉，显示出双侧和径向对称。然而，在发育过程中如何出现不同的对称性仍然未知。在这里，我们报告了在 D. lineata（Diadumenidae，Actiniaria）中胃袋、肌肉和虹吸符号的对称排列的种内变化，虹吸符号是将水注入生物体的 Anthozoan 特定器官。我们发现内脏的位置排列显然受限于双径向或双侧对称，具体取决于虹吸符号的数量。根据形态学观察，内部器官定位的数学模型被用来预测负责双径向和双侧对称性的发育背景。在模型中，我们假设胃袋的规格是由侧向抑制和激活协调的，这会导致不同的对称性，具体取决于虹吸符号的数量。因此，我们建议一个共同的发育程序可以根据早期发育阶段形成的虹吸符号的数量产生双边或双径向对称。