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.

中文翻译：

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Echiuran 解剖学和组织学的新数据：以 Lissomyema mellita（Annelida：Thalassematidae）为例

Echiura 是一小群未分节的海洋蠕虫，有时在世界海洋所有区域的底栖动物中都很丰富。echiuran 形态学和解剖学的研究对于了解 echiuran 生物学和 echiurans 占主导地位的底栖群落的功能很重要。目前的研究使用石蜡组织学、扫描电子显微镜和 3D 重建来描述 Lissomyema mellita 器官系统的解剖结构，它属于 Thalassematinae 亚科的 Thalassematini 部落。L. mellita 的身体由一个躯干和一个长鼻组成。躯干终止于肛门叶，其中包含许多大腺体，其分泌物可用于处理发现研究动物的坚硬基质。长鼻有横向纤毛沟< 7 μm 宽，可能用于收集和分离食物颗粒。体腔分为长鼻体腔和躯干体腔。长鼻体腔的位置可能表明长鼻来自一个假设的分段的 Echiuran 祖先身体的口腔部分。前肠的短小和组织学均匀性表明 L. mellita 以不需要机械加工的软食物颗粒为食。循环系统具有复杂的组织结构，并包含一些以前在 echiurans 中没有描述过的血管成分：前肠周围的大量神经丛、大量的背侧和腹侧腔隙，以及神经肠和循环血管之间的额外血管。背侧血管很短；环毛血管不存在。L. mellita 的大部分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关于 echiuran 解剖学知识的普遍稀缺性。新发现的特征应纳入echiuran组织的总体方案。