Spermiogenesis in two species ofNebalia leach (crustacea,malacostraca, phyllocarida)

Summary Spermiogenesis inNebalia pugettensis andN. sp. of the subclass Phyllocarida was investigated by transmission electron microscopy. Spermiogenesis is almost identical in the two species. Early spermatids are found in groups with several nuclei in a common cytoplasm. Specializations of the cell surface appear as small, scattered dense knobs underlying the cell membrane. The spermatids become separated but are kept together by a surrounding vegetative cell, which produces a hyaline secretion. The secretion hardens to a capsule surrounding a number of spermatids. Maturation of the spermatids takes place within the secretion. The cells become dense and compact, the cytoplasm vacuolizes, and the mitochondria show signs of degeneration. The centrioles disappear and the surface of the cell becomes irregular and spiny, as the knobs, present in the early spermatids, develop into small spines. Spermatozoa from a spermatophore are small and compact spiny cells without polarity, with a vacuolized cytoplasm and degenerating mitochondria. Acrosomal structures and axonema or flagellum are absent in all developmental stages of theNebalia sperm.