Spermatogenesis in Octomacrum lanceatum (Monogenoidea, oligonchoinea, mazocraeidea).

Ultrastructural aspects of spermatozoon development and morphology in Octomacrum lanceatum are presented. Spermiogenesis involves development of zones of differentiation from the surface of cytophores followed by formation of a middle cytoplasmic process and 2 free flagella whose axonemes form from basal bodies located within each zone of differentiation. The mitochondrion and nucleus penetrate through the zone of differentiation into the middle cytoplasmic process. An intercentriolar body is present. Initially the axes of the basal bodies are perpendicular to that of the intercentriolar body but subsequently rotate about 90 degrees to parallel positions as the flagella develop. Flagella are initially free, but eventually fuse with the middle cytoplasmic process from the proximal to distal end (proximodistal fusion). Subsurface microtubules occur within the zone of differentiation but are lacking from the lateral regions of the middle cytoplasmic process. The mature sperm possesses two axonemes, one mitochondrion, and a complete ring of cortical microtubules (sperm pattern 1). The finding of sperm pattern 1 in the Octomacridae suggests that many features of the spermatozoon of the Diplozoidae are autapomorphic.