Aix-Marseille Université, Marseille, France.
Biological Faculty, Moscow State University, Moscow, Russia.
J Morphol. 2022 Jun;283(6):771-782. doi: 10.1002/jmor.21470. Epub 2022 Apr 14.
Many data on echiurid anatomy and ultrastructure are obtained for Bonellia viridis and extrapolated to other species. The ultrastructure of the axial blood vessels, which has been described as an "osmotic pump," is regarded as one of the unusual features of echiurids. In this study, the ultrastructure of the proboscis blood vessels in females of B. viridis is described, illustrated by accurate schemes, and a new reconstruction of the axial blood vessel is suggested. The walls of the axial and lateral vessels of the proboscis are formed by myoepithelial cells, which are connected to each other via adherence junctions, underlined by basal lamina, and therefore form a true epithelium. Apical, middle, and basal parts of the myoepithelial cells form long, thin projections, which extend to the connective tissue (in axial vessel) or coelomic canals (in lateral vessels) and to the lumen of the vessels. The presence of such projections may evidence active cellular transport. Similarity in the fine structure of the myoepithelial cells of axial and lateral blood vessels evidence their common origin from myoepithelial cells of the coelomic lining. However, in evolution, the coelomic canals were retained around the lateral vessels and disappeared around the axial vessel. The reduction of a hypothetical ancestral axial coelom may be caused by the extensive development of the connective tissue and muscles in the central part of the proboscis, where the axial vessel extends.
许多关于帚虫解剖结构和超微结构的数据是通过对绿帚虫（Bonellia viridis）进行研究获得的，并被推断应用于其他物种。帚虫轴向血管的超微结构被描述为一种“渗透泵”，被认为是帚虫的一个不寻常特征。本研究描述了绿帚虫雌性个体吻部血管的超微结构，并用准确的示意图进行了说明，并提出了一种轴向血管的新重建方法。吻部的轴向和侧血管的壁由肌上皮细胞形成，它们通过粘着连接相互连接，基底膜下面有连接，因此形成真正的上皮。肌上皮细胞的顶端、中部和基部分别形成长而细的突起，这些突起延伸到结缔组织（在轴向血管中）或体腔管（在侧血管中）和血管的腔中。这种突起的存在可能表明存在活跃的细胞运输。轴向和侧血管的肌上皮细胞的超微结构相似，表明它们具有共同的起源，来自体腔衬里的肌上皮细胞。然而，在进化过程中，侧血管周围的体腔管被保留下来，而轴向血管周围的体腔管则消失了。假设祖先轴向体腔的减少可能是由于吻部中央部分的结缔组织和肌肉的广泛发育，轴向血管在此处延伸。
