Moscow State University, Biological Faculty, Dept. Invertebrate Zoology, Leninskie Gory 1, bld. 12, 119991, Moscow, Russia.
A. V. Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Palchevskogo str. 17, 690041, Vladivostok, Russia.
Zoology (Jena). 2021 Feb;144:125865. doi: 10.1016/j.zool.2020.125865. Epub 2020 Nov 6.
Echiura is small group of unsegmented marine worms that are sometimes abundant in the benthos of all areas of the World Ocean. The study of echiuran morphology and anatomy is important for understanding echiuran biology and the function of benthic communities where echiurans dominate. The current study used paraffin histology, scanning electron microscopy, and 3D reconstruction to describe the anatomy of organ systems in Lissomyema mellita, which is within the tribe Thalassematini of the subfamily Thalassematinae. The body of L. mellita consists of a trunk and a proboscis. The trunk terminates at the anal lobe, which contains many large glands, the secretions of which may be used for processing of the hard substratum where studied animals were found. The proboscis has lateral ciliated grooves that are < 7 μm wide and are probably used for collecting and separating food particles. The coelom is divided into the coelom of the proboscis and the coelom of trunk. The location of proboscis coelom may suggest that the proboscis is derived from the oral segment of the body of a hypothetical segmented echiuran ancestor. The shortness and histological uniformity of the foregut indicates that L. mellita feeds on soft food particles that do not require mechanical processing. The circulatory system has a complex organization and contains several vascular elements that have not been previously described in echiurans: voluminous plexus around the foregut, voluminous dorsal and ventral lacunes, and additional vessels between neurointestinal and circular blood vessels. The dorsal blood vessel is very short; the circumchaetael vessel is absent. Most of the anatomical peculiarities of L. mellita appear to be related to its biology. The newness of the data on the organization of the circulatory system reflects the general scarcity of knowledge on echiuran anatomy. The newly discovered features should be incorporated into general schemes of echiuran organization.
环节动物是一小群无节的海洋蠕虫，有时在世界海洋的所有区域的海底中都很丰富。研究环节动物的形态和解剖结构对于理解环节动物的生物学和环节动物占主导地位的底栖群落的功能非常重要。本研究使用石蜡组织学、扫描电子显微镜和 3D 重建技术来描述 Thalassematinae 亚科 Thalassematini 族中的 Lissomyema mellita 的器官系统解剖结构。L. mellita 的身体由一个躯干部和一个吻部组成。躯干部在肛门叶处终止，肛门叶包含许多大型腺体，其分泌物可能用于处理研究动物所在的硬底质。吻部有侧生的纤毛沟，宽 < 7μm，可能用于收集和分离食物颗粒。体腔分为吻部体腔和躯干部体腔。吻部体腔的位置可能表明吻部是由假想的有节环节动物祖先的口部体节衍生而来的。前肠的短度和组织学均匀性表明，L. mellita 以软食物颗粒为食，这些颗粒不需要机械处理。循环系统具有复杂的组织，包含几个以前在环节动物中未描述过的血管元素：大量围绕前肠的丛，大量的背侧和腹侧腔隙，以及神经肠和环血管之间的额外血管。背血管非常短；无环毛血管。L. mellita 的大多数解剖学特征似乎与其生物学有关。关于循环系统组织的数据的新颖性反映了环节动物解剖学知识的普遍匮乏。新发现的特征应该被纳入环节动物组织的一般方案中。
