During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral “metamorphoses” to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium’s outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.

在其不同的生命阶段，寄生虫会经历明显的形态，生理和行为“变形”，以满足其不断变化的栖息地的需求。对于外寄生虫，例如单基因的寄生虫，甚至是正确的，它们通常具有一个自由游动的幼虫阶段（尾酸科），该阶段寻找并附着在它们成熟的鱼的外表面上。在任何明显的变化发生之前，在甲氨蝶呤的外表面存在超微结构差异，这为寄生虫的存在做好了准备。目前的发现表明，从表皮开胃到表皮的合胞体结构转换的时机有明显的变化，因此，迄今为止，单基因组中存在三种此类类别：（1）在胚胎发生的后期，纤毛细胞和纤毛间的细胞核都从表层脱落，表皮变成合胞体层；（2）纤毛细胞核和睫状体合胞体的细胞核均保持不同，并且在痛性酸孵化后（如本研究一样）发生转换。（3）在纤毛表皮中细胞核仍然不同，但在胚胎发育过程中，纤毛间表皮的细胞核丢失了。在这里，我们描述了甲胎蛋白的表皮如何 （3）在纤毛表皮中细胞核仍然不同，但在胚胎发育过程中，纤毛间表皮的细胞核丢失了。在这里，我们描述了甲胎蛋白的表皮如何 （3）在纤毛表皮中细胞核仍然不同，但在胚胎发育过程中，纤毛间表皮的细胞核丢失了。在这里，我们描述了甲胎蛋白的表皮如何Discocotyle sagittata分为两个区域，一个纤毛细胞层和一个纤毛间质细胞质，两者都是有核的。睫状体合胞体在纤毛细胞之间和下方延伸，有时覆盖其顶端表面的一部分，可能是脱落过程的开始。表面上存在膜状涡旋和致密性核，表明膜周转，表明在此阶段表皮形态的转换已经开始。人体皮层和亚成体和成年的相关假定的感受器D. sagittata的是类似于在其他单殖吸虫。