Cilia are widely present in metazoans and have various sensory and motor functions, including collection of particles through feeding currents in suspensivorous animals. Suspended particles occur at low densities and are too small to be captured individually, and therefore must be concentrated. Animals that feed on these particles have developed different mechanisms to encounter and capture their food. These mechanisms occur in three phases: (i) encounter; (ii) capture; and (iii) particle handling, which occurs by means of a cilia-generated current or the movement of capturing structures (e.g. tentacles) that transport the particle to the mouth. Cilia may be involved in any of these phases. Some cnidarians, as do other suspensivorous animals, utilise cilia in their feeding mechanisms. However, few studies have considered ciliary flow when examining the biomechanics of cnidarian feeding. Anthozoans (sessile cnidarians) are known to possess flow-promoting cilia, but these are absent in medusae. The traditional view is that jellyfish capture prey only by means of nematocysts (stinging structures) and mucus, and do not possess cilia that collect suspended particles. Herein, we first provide an overview of suspension feeding in invertebrates, and then critically analyse the presence, distribution, and function of cilia in the Cnidaria (mainly Medusozoa), with a focus on particle collection (suspension feeding). We analyse the different mechanisms of suspension feeding and sort them according to our proposed classification framework. We present a scheme for the phases of pelagic jellyfish suspension feeding based on this classification. There is evidence that cilia create currents but act only in phases 1 and 3 of suspension feeding in medusozoans. Research suggests that some scyphomedusae must exploit other nutritional sources besides prey captured by nematocysts and mucus, since the resources provided by this diet alone are insufficient to meet their energy requirements. Therefore, smaller particles and prey may be captured through other phase-2 mechanisms that could involve ciliary currents. We hypothesise that medusae, besides capturing prey by nematocysts (present in the tentacles and oral arms), also capture small particles with their cilia, therefore expanding their trophic niche and suggesting reinterpretation of the trophic role of medusoid cnidarians as exclusively plankton predators. We suggest further study of particle collection by ciliary action and its influence on the biomechanics of jellyfishes, to expand our understanding of the ecology of this group.

中文翻译：

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纤毛在水生动物摄食机制中的作用综述

纤毛广泛存在于后生动物中，具有各种感觉和运动功能，包括通过悬食动物的摄食流收集颗粒。悬浮颗粒的密度较低且太小而无法单独捕获，因此必须进行浓缩。以这些颗粒为食的动物已经发展出不同的机制来遇到和捕获食物。这些机制分三个阶段发生：（i）相遇； ( ii )捕获； ( iii )颗粒处理，其通过纤毛产生的电流或将颗粒输送至口腔的捕获结构（例如触手）的运动来进行。纤毛可能参与这些阶段的任何一个。一些刺胞动物和其他悬食动物一样，在其进食机制中利用纤毛。然而，很少有研究在检查刺胞动物进食的生物力学时考虑纤毛流动。已知珊瑚动物（无柄刺胞动物）具有促进流动的纤毛，但水母科中不存在这些纤毛。传统观点认为，水母仅通过刺丝囊（刺结构）和粘液捕获猎物，并且不具有收集悬浮颗粒的纤毛。在此，我们首先概述无脊椎动物的悬浮摄食，然后批判性地分析刺胞动物（主要是水母动物）中纤毛的存在、分布和功能，重点是颗粒收集（悬浮摄食）。我们分析了悬浮喂养的不同机制，并根据我们提出的分类框架对它们进行了分类。我们根据这种分类提出了中上层水母悬浮喂养阶段的方案。有证据表明，纤毛会产生电流，但仅在水生动物悬浮摄食的第一阶段和第三阶段起作用。研究表明，除了刺丝囊和粘液捕获的猎物之外，一些镰刀科动物还必须利用其他营养来源，因为仅靠这种饮食提供的资源不足以满足它们的能量需求。因此，较小的颗粒和猎物可以通过其他可能涉及纤毛电流的第二阶段机制来捕获。我们假设水母除了通过线虫囊（存在于触手和口臂中）捕获猎物外，还用纤毛捕获小颗粒，从而扩大其营养生态位，并建议重新解释水母刺胞动物作为专门的浮游生物捕食者的营养作用。我们建议进一步研究纤毛作用的颗粒收集及其对水母生物力学的影响，以扩大我们对该群体生态学的了解。