The fine structure of the conical-headed sperm of the crinoidAntedon bifida

Summary Scanning- and transmission electron microscopy show that the sperm head ofAntedon bifida is conical and thus different from the spherical sperm head that is typical of crinoids. The head consists of the acrosome and the nucleus. The posterior fibrogranular component of the acrosome is housed in a tubular, axial invagination running from the anterior pole almost to the posterior pole of the nucleus. The middle piece includes a mitochondrion and a pair of centrioles. One of the centrioles is a basal body, which gives rise to the tail flagellum.