Table 4.

Ciliary mechanosensory cells in proprioception.

animal group	species	stage	cell name (s)	evidence of mechanosensory modality	molecular dataa	sensory neuron (SN) or secondary sensory cell (SSC)b	cilium features	actin or other structures	location of cells
Cnidaria	Hydra spp. [350–352]	polyp	sensorimotor interneuron	—	—	SN	— uniciliated — recessed cilium — cilium partially exposed to the muscle-epithelial cells — thick rootlets — acellular cavity at the ciliary necklace region — 9 doublets plus 6 singlets microtubule-membrane connections (MMCs)	— three concentric rings of microvilli arise opposite to the cilium — fibrous connections between cilium and microvilli	— tentacles — hypostome
Cnidaria	Ceriantheopsis americanus [349]	polyp	bipolar mechanoreceptor	—	—	SN	— uniciliated — 9+2 axoneme — >16 µm long cilium embedded in muscle- epithelial cell — MMCs — long-thick rootlet	— collar of 6–8 stereovilli — sensory apparatus and dendrite interdigitates with the epitheliomuscular cell	— body wall
Nematoda	Deontostoma californicum [353]	—	proprioceptor metaneme [353]	—	—	SSC	— uniciliated — 9+0 axoneme — 3.5 µm long cilium — thick long rootlet, sometimes extending into the cilium	— 6–7 fibrous lobes surrounding cilium and arising opposite the cilium — ridges fuse near base of cilia — filaments connecting lobes and cilium	— hypodermal lateral nerve cords

^aOnly molecular data related to the expression of mechanotransduction-related components is included.

^bSecondary sensory cells lack a neurite projection (e.g. vertebrate hair cells).