Some aspects of the fine structure of the statocysts of the molluscsPecten andPterotrachea

Summary The statocyst ofPecten is composed of hair cells and supporting cells. The hair cells bear kinocilia and microvilli at their distal ends and the supporting cells bear microvilli. The cilia have a 9+2 internal filament content, and arise from basal bodies that have roots, basal feet and microtubular connections. Two different ciliary arrangements are described, one with a small number of cilia arranged in a ring, and another with many more cilia arranged in rows. Below the hair cells are probable synapses. A ciliated duct connects to the lumen of the static sac and passes through the centre of the static nerve. The hair cells in the statocyst ofPterotrachea bear kinocilia and microvilli. The possible importance of cilia and microvilli in the transduction process is discussed.We would like to thank ProfessorJ. Z. Young for bringing specimens ofPterotrachea from Naples and also the staff of the Stazione Zoologica for the provision of specimens, Dr.M. Land for providing specimens ofPecten, the Science Research Council (U.K.) for providing the electron microscope used in much of the study and also for a grant to one of us (V.C.B.), and Mrs.J. Parkers and Mr.R. Moss and Mrs.J. Hamilton for much photographic and technical assistance.