The Oweniidae are marine annelids with many unusual features of organ system, development, morphology, and ultrastructure. Together with magelonids, oweniids have been placed within the Palaeoannelida, a sister group to all remaining annelids. The study of this group may increase our understanding of the early evolution of annelids (including their radiation and diversification). In the current research, the morphology and ulta-anatomy of the head region of Owenia borealis is studied by scanning electron microscopy (SEM), 3D reconstructions, transmission electron microscopy (TEM), and whole-mount immunostaining with confocal laser scanning microscopy. According to SEM, the tentacle apparatus consists of 8–14 branched arms, which are covered by monociliary cells that form a ciliary groove extending along the oral side of the arm base. Each tentacle contains a coelomic cavity with a network of blood capillaries. Monociliary myoepithelial cells of the tentacle coelomic cavity form both the longitudinal and the transverse muscles. The structure of this myoepithelium is intermediate between a simple and pseudo-stratified myoepithelium. Overall, tentacles lack prominent zonality, i.e., co-localization of ciliary zones, neurite bundles, and muscles. This organization, which indicates a non-specialized tentacle crown in O. borealis and other oweniids with tentacles, may be ancestral for annelids. TEM, light, and confocal laser scanning microscopy revealed that the head region contains the anterior nerve center comprising of outer and inner (=circumoral) nerve rings. Both nerve rings are organized as concentrated nerve plexus, which contains perikarya and neurites extending between basal projections of epithelial cells (radial glia). The outer nerve ring gives rise to several thick neurite bundles, which branch and extend along aboral side of each tentacle. Accordingly to their immunoreactivity, both rings of the anterior nerve center could be homologized with the dorsal roots of circumesophageal connectives of the typical annelids. Accordingly to its ultrastructure, the outer nerve ring of O. borealis and so-called brain of other oweniids can not be regarded as a typical brain, i.e. the most anterior ganglion, because it lacks ganglionic structure.

中文翻译：

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Owenia borealis (Annelida, Oweniidae) 触手器官和中枢神经系统的详细形态

Oweniidae 是海洋环节动物，具有许多不同寻常的器官系统、发育、形态和超微结构特征。与 magelonids 一起，oweniids 被放置在 Palaeoannelida 中，这是所有剩余环节动物的姊妹组。对这个群体的研究可能会增加我们对环节动物早期进化（包括它们的辐射和多样化）的理解。在目前的研究中，通过扫描电子显微镜 (SEM)、3D 重建、透射电子显微镜 (TEM) 和共聚焦激光扫描显微镜的整体免疫染色研究了 Owenia borealis 头部区域的形态和 ulta-anatomy。根据 SEM，触手装置由 8-14 个分支臂组成，这些臂被单纤毛细胞覆盖，形成沿臂基口侧延伸的睫状沟。每个触手都包含一个带有毛细血管网络的体腔。触手体腔的单纤毛肌上皮细胞形成纵向和横向肌肉。这种肌上皮的结构介于简单和假复层肌上皮之间。总体而言，触手缺乏突出的地带性，即睫状区、神经突束和肌肉的共定位。这个组织表明 O.borealis 和其他有触手的 oweniids 有一个非特化的触手冠，可能是环节动物的祖先。TEM、光和共聚焦激光扫描显微镜显示头部区域包含前神经中枢，包括外神经环和内神经环（=周围）。两个神经环都组织成集中的神经丛，它包含在上皮细胞（径向神经胶质）的基底突起之间延伸的核膜和轴突。外神经环产生几个厚的神经突束，它们沿着每个触手的背侧分支和延伸。根据它们的免疫反应性，前神经中枢的两个环可以与典型环节动物的食管周围结缔组织的背根同源。根据其超微结构，O.borealis 的外神经环和其他牛脑的所谓大脑不能被视为典型的大脑，即最前神经节，因为它缺乏神经节结构。前神经中枢的两个环可以与典型环节动物的食管周围结缔组织的背根同源。根据其超微结构，O.borealis 的外神经环和其他牛脑的所谓大脑不能被视为典型的大脑，即最前神经节，因为它缺乏神经节结构。前神经中枢的两个环可以与典型环节动物的食管周围结缔组织的背根同源。根据其超微结构，O.borealis 的外神经环和其他牛脑的所谓大脑不能被视为典型的大脑，即最前神经节，因为它缺乏神经节结构。