Mudskippers are amphibious fishes that use their pectoral fins to move on land. Their pectoral fins are specifically modified for terrestrial locomotion. Studies of the anatomy and kinematics of adult mudskippers suggest that modifications of the pectoral fins, such as their protrusion and elongation of the proximal radials, may provide greater control and flexibility in pectoral fin–based locomotion. However, it is unknown when and how the unique features of these pectoral fins form during the development of mudskippers, which begin life as a planktonic organism. Here we examined the developmental process of the pectoral fins of the mudskipper Periophthalmus modestus to address these questions. We also observed other developmental characteristics to provide clarified descriptions, including indicative morphological changes that occur during metamorphosis. Our results show that the localized cell division of the proximal part of the endoskeletal disc—the primordium of the proximal radials—and subsequent cell division along the proximal-distal axis, which is restricted to the distal part of the disc during the larva-to-juvenile transition (metamorphosis), lead to the elongation of the proximal radials.

中文翻译：

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在弹涂鱼（Periophthalmus modetus）的幼虫向幼鱼过渡期间发生胸鳍的修饰

弹涂鱼是两栖鱼类，它们利用胸鳍在陆地上移动。它们的胸鳍专门针对陆地运动进行了改造。对成年弹涂鱼的解剖学和运动学的研究表明，胸鳍的修改，例如它们的近端桡骨的突出和伸长，可以在基于胸鳍的运动中提供更大的控制和灵活性。然而，在弹涂鱼的发育过程中，这些胸鳍的独特特征何时以及如何形成尚不清楚，弹涂鱼是作为浮游生物开始生命的。在这里，我们研究了弹涂鱼 Periophthalmus modetus 胸鳍的发育过程，以解决这些问题。我们还观察了其他发育特征以提供清晰的描述，包括变态过程中发生的指示性形态变化。我们的研究结果表明，内骨骼椎间盘近端部分的局部细胞分裂 - 近端桡骨的原基 - 以及随后沿近端 - 远端轴的细胞分裂，其在幼虫期间仅限于椎间盘的远端部分。 - 幼年过渡（变态），导致近端桡骨伸长。