Most morphological studies focus on adult specimens, or if developmental studies are pursued, especially in Euarthropoda, they focus on embryonic development. Araneae (spiders) is one of these groups, in consequence with understudied post-embryonic development. Here we present aspects of the post-embryonic stages of different species of Mesothelae, sister group to the remaining spiders (when fossil species are not taken into account). We used different imaging methods and measured different external morphological structures to detect possible ontogenetic changes. One structure exhibiting post-embryonic changes is the chelicera. Here the significant change occurs between the last immature stage and the adult, yet only in males. For the spinnerets, we could not detect ontogenetic changes, but instead a high variability in length and width, probably due to their lack of pivot joints between the elements. The strongest morphological change during ontogeny occurred on the sternum, which begins with a rather roundish shape in the first stage and changes to being fairly elongate in shape in the last immature stages and the adult. This specific sternum shape only occurs in adults of mesothelan spiders, while opisthothelan spiders have a broader sternum also in the adult. We discuss our results in an evolutionary context, also taking into account recent finds of fossil spiders.

大多数形态学研究都集中在成年标本上，或者如果进行发育研究，特别是在真节肢动物中，则它们侧重于胚胎发育。Araneae（蜘蛛）是这些群体之一，因此对胚胎后发育的研究不足。在这里，我们展示了不同物种间皮的胚胎后阶段，其余蜘蛛的姐妹群（当不考虑化石物种时）。我们使用不同的成像方法并测量不同的外部形态结构来检测可能的个体遗传变化。一种表现出胚胎后变化的结构是螯肢。此处的显着变化发生在最后未成熟阶段和成年之间，但仅发生在雄性身上。对于喷丝头，我们无法检测到个体发生的变化，而是长度和宽度的高度可变性，可能是由于它们在元件之间缺少枢轴接头。个体发育过程中最强烈的形态变化发生在胸骨，在第一阶段开始呈相当圆的形状，在最后的未成熟阶段和成虫阶段变为相当细长的形状。这种特殊的胸骨形状只发生在间皮蜘蛛的成虫身上，而反面蜘蛛的成虫也有更宽的胸骨。我们在进化背景下讨论我们的结果，同时考虑到最近发现的蜘蛛化石。这种特殊的胸骨形状只发生在间皮蜘蛛的成虫身上，而反面蜘蛛的成虫也有更宽的胸骨。我们在进化背景下讨论我们的结果，同时考虑到最近发现的蜘蛛化石。这种特殊的胸骨形状只发生在间皮蜘蛛的成虫身上，而反面蜘蛛的成虫也有更宽的胸骨。我们在进化背景下讨论我们的结果，同时考虑到最近发现的蜘蛛化石。