The apical organ of ctenophores is the center of sensory information that controls locomotion. Previous studies have described several types of cilia in this organ. However, detailed ciliary structures, particularly axonemal structures, have not been extensively investigated. Here, we reported that the apical organ of the ctenophore Bolinopsis mikado contains six types of cilia with different axonemal structures. These include the typical “9 + 2” motile axonemes, with both outer and inner dynein arms, only the inner dynein arm, or no dynein arm; axonemes with electron‐dense structures in the A‐tubules; “9 + 0” axonemes lacking the central pair of microtubules; and axonemes with compartmenting lamellae. Considering that “9 + 2” axonemal structures with both dynein arms are thought to be ancestral forms of cilia, the apical organ of ctenophores would comprise an elaborate assembly of modified ciliary forms that sense and transmit extracellular stimuli and generate various fluid flows.

中文翻译：

---

栉水母 Bolinopsis mikado 顶端感觉器官纤毛的结构多样性和分布

栉水母的顶端器官是控制运动的感觉信息的中心。先前的研究描述了该器官中的几种纤毛类型。然而，详细的纤毛结构，特别是轴索结构，尚未得到广泛研究。在这里，我们报道了栉水母Bolinopsis mikado的顶端器官包含六种不同轴索结构的纤毛。这些包括典型的“9 + 2”运动轴丝，具有外部和内部动力蛋白臂，只有内部动力蛋白臂，或没有动力蛋白臂；在 A 小管中具有电子致密结构的轴丝；“9 + 0”轴丝缺乏中央微管对；和轴丝与分隔薄片。考虑到带有两个动力蛋白臂的“9 + 2”轴突结构被认为是纤毛的祖先形式，栉水母的顶端器官将包含一个精心组装的修饰纤毛形式，这些纤毛形式感知和传递细胞外刺激并产生各种流体流动。