Copepoda is one of the crustacean taxa with still unresolved phylogenetic relationships within Tetraconata. Recent phylogenomic studies place them close to Malacostraca and Cirripedia. Little is known about the morphological details of the copepod nervous system, and the available data are sometimes contradictory. We investigated several representatives of the subgroup Calanoida using immunohistochemical labeling against alpha-tubulin and various neuroactive substances, combining this with confocal laser scanning analysis and 3D reconstruction. Our results show that the studied copepods exhibit only a single anterior protocerebral neuropil which is connected to the nerves of two protocerebral sense organs: the frontal filament organ and a photoreceptor known as the Gicklhorn's organ. We suggest, on the basis of its position and the innervation it provides, that Gicklhorn's organ is homologous to the compound eye in arthropods. With regard to the frontal filament organ, we reveal detailed innervation to the lateral protocerebrum and the appearance of spherical bodies that stain intensely against alpha tubulin. A potential homology of these bodies to the onion bodies in malacostacan crustaceans and in Mystacocarida is suggested. The nauplius eye in all the examined calanoids shows the same basic pattern of innervation with the middle cup sending its neurites into the median nerve, while the axons of the lateral cups proceed into both the median and the lateral nerves. The early development of the axonal scaffold of the nauplius eye neuropil from the proximal parts of the nauplius eye nerves follows the same pattern as in other crustaceans. In our view, this specific innervation pattern is a further feature supporting the homology of the nauplius eye in crustaceans.

中文翻译：

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颅骨co足类动物的大脑和相应的感觉器官-复眼痕迹的证据。

pe足类是甲壳纲类群之一，在四齿纲内仍未解决系统发育关系。最近的植物遗传学研究使它们靠近马拉科斯特拉和Cirripedia。关于co足类神经系统的形态学细节知之甚少，可用数据有时是矛盾的。我们使用针对α-微管蛋白和各种神经活性物质的免疫组织化学标记，结合共焦激光扫描分析和3D重建，研究了Calanoida亚组的几个代表。我们的结果表明，所研究的co足类动物仅表现出一个与两个前脑感觉器官（额叶细丝器官和一个称为Gicklhorn器官）的神经连接的神经元。我们建议，根据其位置和提供的支配，吉克霍恩的器官与节肢动物的复眼同源。关于额叶细丝器官，我们揭示了对侧前脑的详细神经支配以及对α微管蛋白强烈染色的球形体的外观。建议在马拉古斯塔康甲壳类动物和Mycarcocarida中这些体与洋葱体的潜在同源性。在所有检查过的类颅神经中，无节幼体的眼睛显示出相同的基本神经支配模式，其中中杯将其神经突送入正中神经，而侧杯的轴突则同时进入正中神经和侧神经。从无节眼睛神经的近端开始，无节眼睛神经纤维的轴突支架的早期发育与其他甲壳类动物相同。我们认为，这种特定的神经支配方式是支持甲壳纲中无节幼体眼睛同源性的又一特征。