Development of the nervous system of sea urchin embryos : formation of ciliary bands and the appearance of two types of ectoneural cells in the pluteus

摘要: An ultrastructural study of the larval integument sea urchin, Hemicentrotus pulcherrimus, was conducted with special emphasis on development nervous system in relation to formation ciliary bands. In 4-armed pluteus larvae, cells associated band, which have 200 nm-thick projections at their apices, and squamous epithelium, a cilium long, fine radiating processes apical region, were observed. Both cell types axons basal ends that form nerve bundles beneath bands, where make contact ectodermal effector motile cilia. The cilia other these ectoneural run parallel surface cells, are under hyaline layer. axoneme has typical “9 + 2” microtubular arrangement, but generally no dynein arms. These more frequent oral than antioral surface.