Spermiogenesis in the anthozoan Aiptasia pallida

Fine structural aspects of spermiogenesis in the anthozoan Aiptasia pallida have been examined. Nuclear condensation is similar to that reported for other anthozoans. The middle piece is formed by fusion of a few small mitochondria and is doughnut-shaped. A well-developed centriolar complex is attached to the nuclear envelope by fine filamentous material and is surrounded by the mitochondrial collar. Electron-dense vesicles, which correspond to 'proacrosomal vesicles', are scattered in the peripheral cytoplasm at the nuclear-mitochondrial junction. Cytochemical procedures indicate that these vesicles contain carbohydrates and basic proteins, suggesting they may be acrosomal-like.