Lomonosov Moscow State University, Biological Faculty, Dept. of Invertebrate Zoology, Leninskie Gory 1-12, 119991, Moscow, Russia.
Lomonosov Moscow State University, Biological Faculty, Dept. of Invertebrate Zoology, Leninskie Gory 1-12, 119991, Moscow, Russia; National Research University Higher School of Economics, Faculty of Biology and Biotechnology, Myasnitskaya 20, 101000, Moscow, Russia.
Zoology (Jena). 2021 Feb;144:125884. doi: 10.1016/j.zool.2020.125884. Epub 2020 Nov 21.
Brachiopoda is a relict phylum of marine benthic animals that have not been adequately studied with modern microscopy methods. Microscopic study may provide useful information on the evolution of the brachiopod body plan and brachiopod phylogeny. Understanding the organisation of the coelomic system is important because of its role in body form and compartmentalisation. Most brachiopods are considered to have a bipartite coelomic system; the only known exception is Lingulida, which have a tripartite coelomic system. In the present study, we provide the first complete 3D reconstruction of the coelomic system in the craniide brachiopod Novocrania anomala (Müller, 1776). Its coelomic system consists of the following five main parts, which are entirely separated from each other: 1) a pair of large brachial canals; 2) a complex system of paired small brachial canals and a perioesophageal coelom; 3) frontal coelomic chambers; 4) a main trunk coelom, which includes several semi-detached muscular chambers and mantle sinuses; and 5) a pair of posterior adductors chambers. These results indicate that the coelomic system of N. anomala (and perhaps of other craniides) is complex and cannot be considered to be bipartite or tripartite. The frontmost part of the coelomic system is represented by a pair of frontal chambers, which are considered to be a part of the lophophore but which are derived from dorsal mantle fold extensions and thus may be a part of the trunk coelomic system. A number of similarities were discovered between craniiformean and rhynchonelliformean coelomic systems, including the prominent dorsal projections of the large brachial canals and the morphological features of the perioesophageal coelom. The complex subdivision of the N. anomala trunk coelom is explained by the location and function of muscles, and by the location of several mesenteries.
腕足动物是一类海洋底栖动物的遗迹门，它们尚未通过现代显微镜方法得到充分研究。微观研究可能为腕足动物身体结构的进化和腕足动物系统发育提供有用的信息。了解体腔系统的组织对于身体形态和分隔至关重要。大多数腕足动物被认为具有二分体腔系统；唯一已知的例外是舌形贝目，它们具有三分体腔系统。在本研究中，我们首次提供了腕足动物 Novocrania anomala（Müller，1776）体腔系统的完整三维重建。它的体腔系统由以下五个主要部分组成，彼此完全分开：1）一对大腕臂管；2）一个复杂的成对小腕臂管和围食管体腔系统；3）额腔室；4）一个主干体腔，其中包括几个半分离的肌肉腔室和套膜窦；5）一对后收肌腔室。这些结果表明，N. anomala（也许还有其他腕足动物）的体腔系统复杂，不能被认为是二分体腔或三分体腔。体腔系统的最前端由一对额腔室组成，这些额腔室被认为是担轮的一部分，但它们是由背套膜褶皱延伸而来的，因此可能是干体腔系统的一部分。我们发现腕足形目和舌形贝形目的体腔系统之间存在一些相似之处，包括大腕臂管的显著背突和围食管体腔的形态特征。N. anomala 干体腔的复杂细分是由肌肉的位置和功能以及几个系膜的位置决定的。
