The kinetid (flagellar/ciliary apparatus) of eukaryotic cells is an important source of phylogenetic information. It was found to be a prospective morphological phylogenetic marker in sponges, since its arrangement in choanocytes is congruent with the topology of the phylogenetic trees. However, investigation of the kinetid of sponge larval cells remains fragmentary. Here, we report the results of an ultrastructural study on the larval kinetids of the freshwater sponges Eunapius fragilis and Lubomirskia baikalensis (Demospongiae: Spongillida). Their kinetids were found to comprise a kinetosome associated with an accessory centriole and linked to the nucleus by a simple fibrillar root. The kinetosome bears a transverse cytoskeleton: filamentous train and microtubules which radiate from a microtubule organising centre (MTOC) shaped as a large hollow foot. In the short transition zone, between the central axonemal microtubules and kinetosome, a transverse plate with an axosome (central thickening) occurs. We have reviewed the kinetids of different sponge larvae to reconstruct the ancestral state of these traits. Thus, we suggest that spongillids retain the plesiomorphic characteristics of roots and an accessory centriole. But they possess the peculiarities of the transition zone, transverse cytoskeleton and MTOC structure.

中文翻译：

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Spongillida (Porifera: Demospongiae) 幼虫细胞中的动虫：追踪祖先特征

真核细胞的动力学（鞭毛/纤毛器）是系统发育信息的重要来源。它被发现是海绵中一种有前景的形态学系统发育标记，因为它在后尾细胞中的排列与系统发育树的拓扑结构一致。然而，对海绵幼虫细胞动体的研究仍然是零碎的。在这里，我们报告了对淡水海绵 Eunapius fragilis 和 Lubomirskia baikalensis (Demospongiae: Spongillida) 的幼虫动力学的超微结构研究结果。发现它们的动体包括一个与辅助中心粒相关的动体，并通过一个简单的原纤维根与细胞核相连。运动体带有横向细胞骨架：从微管组织中心 (MTOC) 向外辐射的丝状链和微管，其形状为一个大的空心足。在短过渡区，在中央轴突微管和运动体之间，出现带有轴突（中央增厚）的横向板。我们回顾了不同海绵幼虫的动能，以重建这些性状的祖先状态。因此，我们建议海绵体保留了根和辅助中心粒的拟形特征。但它们具有过渡区、横向细胞骨架和MTOC结构的特点。我们回顾了不同海绵幼虫的动能，以重建这些性状的祖先状态。因此，我们建议海绵体保留了根和辅助中心粒的拟形特征。但它们具有过渡区、横向细胞骨架和MTOC结构的特点。我们回顾了不同海绵幼虫的动能，以重建这些性状的祖先状态。因此，我们建议海绵体保留了根和辅助中心粒的拟形特征。但它们具有过渡区、横向细胞骨架和MTOC结构的特点。