In recent years, methods for investigating the exo-morphology of zoological specimens have seen large improvements. Among new approaches, auto-fluorescence imaging offers possibilities to document specimens under high resolution without introducing additional artifacts as, for example, seen in scanning electron microscopy (SEM) imaging. Additionally, while SEM imaging is restricted to the outer morphology of the current instar, auto-fluorescence imaging can be used to document changes of the outer morphology of the next instar underneath the cuticle of the current instar. Thus, reinvestigating seemingly well known species with these methods may lead to interesting new insights. Here we reinvestigate the late embryonic development of the xiphosuran (“sword tail”) Limulus polyphemus, which is often treated as a proxy for early eucheliceratan evolution. In addition to entire specimens, the appendages of the embryos were dissected off and documented separately with composite-autofluorescence microscopy. Based on these data, we can distinguish six developmental stages. These stages do not match exactly the formerly described stages, as these were largely based on SEM investigation. Our stages appear to represent earlier or later phases within what has in other studies been identified as one stage. This finer subdivision is visible as we can see the developing cuticle under the outer cuticle. In comparison to data from fossil xiphosurans, our results and those of other studies on the ontogeny of L. polyphemus point to a derived mode of development in this species, which argues against the idea of L. polyphemus as a “living fossil.”

中文翻译：

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poly虫（Xiphosura s.str。，Euchelicerata）的个体发生了改变：看起来“在皮肤下”。

近年来，研究动物标本的外在形态的方法有了很大的进步。在新方法中，自动荧光成像提供了在不引入其他伪影的情况下以高分辨率记录标本的可能性，例如在扫描电子显微镜（SEM）成像中所见。此外，尽管SEM成像仅限于当前龄期的外表形态，但自体荧光成像技术可用于记录当前龄期表皮下方下一个龄期表层的外部形态变化。因此，用这些方法重新研究看似众所周知的物种可能会产生有趣的新见解。在这里，我们重新调查xiphosuran（“剑尾”）的后期胚胎发育鲎，通常被视为早期桉木进化的代理。除整个标本外，还将胚胎的附件解剖并用复合自发荧光显微镜单独记录。基于这些数据，我们可以区分六个发展阶段。这些阶段与先前描述的阶段不完全匹配，因为这些阶段主要基于SEM研究。在其他研究中，我们的阶段似乎代表了较早或较晚的阶段。可以看到这个更细的细分，因为我们可以看到外部角质层下面的正在发育的角质层。在从化石xiphosurans，我们的结果与其他研究对个体发育比较数据L.波吕斐摩斯指出了该物种的一种衍生发展模式，这与多角乳杆菌作为“生活化石”的想法背道而驰。