基皮新胚层类（扁形动物门）排泄导管的超微结构模式和基生绦虫的新原肾特征。

Ultrastructural patterns of the excretory ducts of basal neodermatan groups (Platyhelminthes) and new protonephridial characters of basal cestodes.

机构信息

Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl Region, 152742, Russia.

Institute of Parasitology, Biology Centre, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic.

出版信息

Parasit Vectors. 2020 Sep 4;13(1):442. doi: 10.1186/s13071-020-04307-8.

DOI:10.1186/s13071-020-04307-8

PMID:32887664

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC7472586/

Abstract

BACKGROUND

The flatworms (Lophotrochozoa: Platyhelminthes) are one of the major phyla of invertebrates but their interrelationships are still not well understood including unravelling the most closely related taxon of the Neodermata, which includes exclusively obligate parasites of all main groups of vertebrates with some 60,000 estimated species. Recent phylogenomic studies indicate that the freshwater 'microturbellarian' Bothrioplana semperi may be the closest ancestor to the Neodermata, but this hypothesis receives little morphological support. Therefore, additional morphological and ultrastructural characters that might help understand interrelations within the Neodermata are needed.

METHODS

Ultrastructure of the excretory ducts of representatives of the most basal parasitic flatworms (Neodermata), namely monocotylid (Monopisthocotylea) and chimaericolid (Polyopisthocotylea) monogeneans, aspidogastreans (Trematoda), as well as gyrocotylidean and amphilinidean tapeworms (Cestoda), were studied using transmission electron microscopy (TEM).

RESULTS

The present study revealed the same pattern of the cytoarchitecture of excretory ducts in all studied species of the basal neodermatans. This pattern is characterised by the presence of septate junctions between the adjacent epithelial cells and lateral ciliary flames along different levels of the excretory ducts. Additionally, a new character was observed in the protonephridial terminal cell of Gyrocotyle urna, namely a septate junction between terminal and adjacent duct cells at the level of the distal extremity of the flame tuft. In Amphilina foliacea, a new type of protonephridial cell with multiple flame bulbs and unique character of its weir, which consists of a single row of the ribs, is described. A remarkable difference has been observed between the structure of the luminal surface of the excretory ducts of the studied basal neodermatan groups and B. semperi.

CONCLUSIONS

The present study does not provide ultrastructural support for a close relationship between the Neodermata and B. semperi.

摘要

背景

扁形动物门（Lophotrochozoa：扁形动物门）是无脊椎动物的主要门之一，但它们的相互关系仍未得到很好的理解，包括揭示新皮动物中最密切相关的分类群，新皮动物仅包括所有主要脊椎动物群体的专性寄生虫，估计约有 6 万种。最近的系统基因组学研究表明，淡水“微涡虫”Bothrioplana semperi 可能是新皮动物的最接近祖先，但这一假设几乎没有形态学支持。因此，需要额外的形态和超微结构特征来帮助理解新皮动物内部的关系。

方法

使用透射电子显微镜（TEM）研究了最基础的寄生扁形动物（新皮动物）的代表，即单叶吸虫（Monopisthocotylea）和嵌合体吸虫（Polyopisthocotylea）单殖吸虫、吸虫（Trematoda），以及旋毛虫和 Amphilinidean 绦虫（Cestoda）的排泄导管的超微结构。

结果

本研究揭示了所有研究的基础新皮动物物种中排泄导管的细胞结构相同。这种模式的特点是相邻上皮细胞之间存在有隔连接，以及沿着排泄导管的不同水平存在侧向纤毛火焰。此外，在 Gyrocotyle urna 的原肾终端细胞中观察到一个新的特征，即在火焰丛的远端末梢水平，终端细胞和相邻导管细胞之间存在有隔连接。在 Amphilina foliacea 中，描述了一种具有多个火焰球和独特的堰特征的原肾细胞，其堰由一排肋骨组成。在研究的基础新皮动物群和 B. semperi 的排泄导管的腔表面结构之间观察到显著差异。