Abstract：
The marine microturbellarian Macrostomum lignano (Platyhelminthes, Rhabditophora) is an emerging laboratory model used by a growing community of researchers because it is easy to cultivate, has a fully sequenced genome, and offers multiple molecular tools for its study. M. lignano has a compartmentalized brain that receives sensory information from receptors integrated in the epidermis. Receptors of the head, as well as accompanying glands and specialized epidermal cells, form a compound sensory structure called the frontal glandular complex. In this study, we used semi-serial transmission electron microscopy (TEM) to document the types, ultrastructure, and three-dimensional architecture of the cells of the frontal glandular complex. We distinguish a ventral compartment formed by clusters of type 1 (multiciliated) sensory receptors from a central domain where type 2 (collar) sensory receptors predominate. Six different types of glands (rhammite glands, mucoid glands, glands with aster-like and perimaculate granula, vacuolated glands, and buckle glands) are closely associated with type 1 sensory receptors. Endings of a seventh type of gland (rhabdite gland) define a dorsal domain of the frontal glandular complex. A pair of ciliary photoreceptors is closely associated with the base of the frontal glandular complex. Bundles of dendrites, connecting the receptor endings with their cell bodies which are located in the brain, form the (frontal) peripheral nerves. Nerve fibers show a varicose structure, with thick segments alternating with thin segments, and are devoid of a glial layer. This distinguishes platyhelminths from larger and/or more complex invertebrates whose nerves are embedded in prominent glial sheaths.
摘要：
海洋微涡轮大型造口木质素（Platyhelminthes，Rhabditophora）是一种新兴的实验室模型，被越来越多的研究人员社区使用，因为它易于培养，有一个完全测序的基因组，并为其研究提供多种分子工具。M.lignano具有分隔的大脑，可从整合在表皮中的受体接收感觉信息。头部的受体，以及伴随的腺体和特殊的表皮细胞，形成一种称为额叶腺体的复合感觉结构。在这项研究中,我们使用半串行透射电子显微镜（TEM）来记录类型，超微结构，和额叶腺体细胞的三维结构。我们将由1型（多纤毛）感觉受体簇形成的腹室与2型（领状）感觉受体占主导地位的中央域区分开。六种不同类型的腺体（莱姆氏腺体，粘液腺，腺体，具星形和周状颗粒，液泡腺体，和扣状腺体）与1型感觉受体密切相关。第七种类型的腺体（横纹肌腺）的末端定义了额叶腺体的背侧。一对睫状光感受器与额叶腺体的基部密切相关。成束的树突，将受体末端与位于大脑中的细胞体连接起来，形成（额叶）周围神经。神经纤维表现为静脉曲张结构,厚段与薄段交替，并且没有神经胶质层。这将扁平蠕虫与较大和/或更复杂的无脊椎动物区分开来，这些无脊椎动物的神经被嵌入突出的神经胶质鞘中。
