title: Development of ciliary bands in larvae of the living isocrinid sea lilyMetacrinus rotundus.
abstract: Embryos and larvae of an isocrinid sea lily,Metacrinus rotundus, are described by scanning electron microscopy. Around hatching (35 h after fertilization), the outer surface of the gastrula becomes ubiquitously covered with short cilia. At 40 h, the hatched swimming embryo develops a cilia-free zone of ectoderm on the ventral side. By 3 days, the very early dipleurula larva develops a cilia-free zone ventrally, densely ciliated regions laterally, and a sparsely ciliated region dorsally. At this stage, the posterior and anterior ciliary bands first appear: the former runs along a low ridge separating the densely from the sparsely ciliated epidermal regions, while the latter is visible, at first discontinuously, along the boundary between the densely ciliated lateral regions and the cilia-free ventral zone. In the late dipleurula larva (5 days after fertilization), the anterior and posterior loops of ciliary bands are well defined. The transition from the dipleurula to the semidoliolaria larva occurs at 6 days as the posterior loop becomes rearranged to form incompletely circumferential ciliary bands. The larva becomes competent to settle at this stage. The arrangement of the ciliary bands on the semidoliolaria is maintained during the second week of development, while the larva retains its competence to settle. The larval ciliary patterns described here are compared with those of stalkless crinoids and eleutherozoan echinoderms. The closest morphological similarities are betweenM. rotundusand the basal eleutherozoan class Asteroidea.
authors: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo Kashiwa, Chiba, 277-8562, Japan ; Marine and Coastal Research Center, Ochanomizu University Ko-yatsu, Tateyama, Chiba, 294-0301, Japan ; Research and Education Center of Natural Sciences, Keio University Yokohama, 223-8521, Japan.
authors: Shonan
authors: S
authors: Amemiya
authors: Faculty of Education, Saitama University, 255 Shimo-Okubo Sakura-ku, Saitama City, 338-8570, Japan.
authors: Taku
authors: T
authors: Hibino
authors: Shimoda Marine Research Center, University of Tsukuba 5-10-1 Shimoda, Shizuoka, 415-0025, Japan.
authors: Hiroaki
authors: H
authors: Nakano
authors: Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University Kakuma, Kanazawa, 920-1192, Japan.
authors: Masaaki
authors: M
authors: Yamaguchi
authors: Research and Education Center of Natural Sciences, Keio University Yokohama, 223-8521, Japan.
authors: Ritsu
authors: R
authors: Kuraishi
authors: Marine and Coastal Research Center, Ochanomizu University Ko-yatsu, Tateyama, Chiba, 294-0301, Japan.
authors: Masato
authors: M
authors: Kiyomoto
keywords: Articulata; Metacrinus rotundus; ciliary band; crinoid; dipleurula; doliolaria; echinoderm; isocrinid; scanning electron microscopy; sea lily
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