Hodová Iveta, Sonnek Radim, Gelnar Milan, Valigurová Andrea
Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, Brno, Czech Republic.
PLoS One. 2018 Feb 7;13(2):e0192285. doi: 10.1371/journal.pone.0192285. eCollection 2018.
Diplozoidae (Monogenea) are blood-feeding freshwater fish gill ectoparasites with extraordinary body architecture and a unique sexual behaviour in which two larval worms fuse and transform into one functioning individual. In this study, we describe the body organisation of Paradiplozoon homoion adult stage using a combined approach of confocal laser scanning and electron microscopy, with emphasis on the forebody and hindbody. Special attention is given to structures involved in functional adaptation to ectoparasitism, i.e. host searching, attachment and feeding/metabolism. Our observations indicate clear adaptations for blood sucking, with a well-innervated mouth opening surrounded by sensory structures, prominent muscular buccal suckers and a pharynx. The buccal cavity surface is covered with numerous tegumentary digitations that increase the area in contact with host tissue and, subsequently, with its blood. The buccal suckers and the well-innervated haptor (with sclerotised clamps controlled by noticeable musculature) cooperate in attaching to and moving over the host. Putative gland cells accumulate in the region of apical circular structures, pharynx area and in the haptor middle region. Paired club-shaped sacs lying laterally to the pharynx might serve as secretory reservoirs. Furthermore, we were able to visualise the body wall musculature, including peripheral innervation, the distribution of uniciliated sensory structures essential for reception of external environmental information, and flame cells involved in excretion. Our results confirm in detail that P. homoion displays a range of sophisticated adaptations to an ectoparasitic life style, characteristic for diplozoid monogeneans.
双身虫科（单殖吸虫纲）是吸食血液的淡水鱼鳃外寄生虫，具有独特的身体结构和性行为，即两个幼虫融合并转变为一个功能个体。在本研究中，我们采用共聚焦激光扫描和电子显微镜相结合的方法描述了同双身虫成虫阶段的身体结构，重点关注前体和后体。特别关注了与外寄生功能适应相关的结构，即宿主搜索、附着和摄食/代谢。我们的观察结果表明，同双身虫对吸血有明显的适应性，其有神经支配良好的开口，周围环绕着感觉结构，有突出的肌肉性口腔吸盘和咽。口腔表面覆盖着许多表皮指状突起，增加了与宿主组织以及随后与宿主血液接触的面积。口腔吸盘和神经支配良好的钩（带有由明显肌肉组织控制的硬化夹子）协同作用，以附着在宿主上并在宿主上移动。推测的腺细胞聚集在顶端圆形结构区域、咽区域和钩的中间区域。位于咽两侧的成对棒状囊可能作为分泌储存器。此外，我们能够观察到体壁肌肉组织，包括外周神经支配、接收外部环境信息所必需的单纤毛感觉结构的分布以及参与排泄的焰细胞。我们的结果详细证实，同双身虫对体外寄生生活方式表现出一系列复杂的适应性，这是双身虫科单殖吸虫的特征。
