The structure of the kinetid (flagellar or ciliary apparatus) is known to be of phylogenetic significance in sponges (Phylum Porifera) and can provide information about evolutionary relationships. Here, we report on the larval kinetid structure of two closely related species, Oscarella lobularis and O. tuberculata (Homoscleromorpha, Oscarellidae). Cells belonging to the four previously recognized morphological regions (anterior pole, lateral zone, paracrystalline belt, and posterior pole) were studied. The cells of the paracrystalline belt have pear‐shaped nuclei with a paracrystalline inclusion connected to the roots of the kinetid. In the cells of other zones, the nucleus is separated from the kinetid, and the roots adjoined the Golgi apparatus only. In kinetids of the studied larval cells, we observed the accessory centriole arranged immediately under the kinetosome, and two unequal fibrillar roots. These features are unique for sponge larvae. Comparing kinetids of the Homoscleromorpha with those in its sister group, the Calcarea, we propose an ancestral composition for the kinetid in the lineage Calcarea + Homoscleromorpha. This proposed kinetid structure includes a kinetosome–nucleus link, striated roots, simple basal foot, orthogonal centriole, and a long transition zone of the flagellum. The position of the centriole under the kinetosome in homoscleromorph larvae and the stout fibrillar or microtubular bundle on the kinetosome in calcarean larvae might be the apomorphies of these groups.

中文翻译：

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两种卵形海绵（类同形海绵）的类褶结构揭示了类同形– are骨沿袭的类形

已知类人动物的结构（鞭毛或睫状体）在海绵（Phylum Porifera）中具有系统发生意义，并可以提供有关进化关系的信息。在这里，我们的两个密切相关的物种幼虫kinetid结构报告，Oscarella lobularis和O. tuberculata（同形异形体，Oscarellidae）。研究了属于四个先前公认的形态学区域（前极，外侧区域，顺晶带和后极）的细胞。准晶带的细胞具有梨形的核，其与准律的根相连。在其他区域的细胞中，细胞核与近端神经节分开，并且其根仅与高尔基体相连。在所研究的幼虫细胞的节肢动物中，我们观察到副中心直接排列在动子体下方，并且有两个不等的须根。这些功能是海绵幼虫特有的。比较同形纲和其同伴群Calcarea的近突，我们提出了Calcarea + Homoscleromorpha谱系中的近祖的祖先组成。拟议的类动植物结构包括一个运动体-核连接，横纹的根，简单的基足，正交的心房和鞭毛的长过渡区。这些同种异型体中，同型变体幼虫在动粒体下方的着丝粒的位置以及在动粒体上的粗纤维或微管束的位置。