Novel bridge of axon-like processes of epithelial cells in the aboral sense organ of ctenophores.

摘要: We describe by light and electron microscopy a novel structure in the aboral sense organ (apical organ) of cydippid (Pleurobrachia) lobate (Mnemiopsis) ctenophores. An elevated bundle long, thin, microtubule-filled processes arises from apical ends two groups epithelial cells located on opposite sides along tentacular plane body. This axon-like arches over floor like bridge, with branches at both running toward opposing pairs ciliary balancers that are motile pacemakers for rows locomotory comb plates. The bridge Pleurobrachia is ∼40 μm long 3–4 wide consists ∼60 closely packed processes, 0.2–0.8 thick, containing vesicles numerous microtubules parallel to their axes. There ∼30 each giving rise cell forms single process, so roughly half must originate one side diverge into pair organ. 150–200 cilia balancer arise morphologically complex cellular projections asymmetric lateral extensions directed towards fork bridge. Presynaptic triad structures found this region but clear examples synaptic contacts between have not yet been traced. Cydippid larvae Mnemiopsis conspicuous Beroid ctenophores lack tentacles all stages do discuss possibility an electrical conduction pathway coordinates tentacle-evoked swimming responses ctenophores, such as global excitation. J. Morphol. 254:99–120, 2002. © 2002 Wiley-Liss, Inc.