Structural and cytochemical features of the sperm of the cephalopod Octopus bimaculatus

Abstract

The aboral region of the spermatophore of the cephalopod Octopus bimaculatus consists of three layers which surround a highly coiled sperm mass. Groups of filamentous spermatozoa, oriented head to tail, are embedded within the flocculent matrix of the sperm mass. The screw-shaped acrosome of the spermatozoon is composed of a granular substance, aggregated at periodic intervals to form striations that are situated perpendicular to the long axis of the sperm. Surrounding the acrosome is a granulofibrillar substance (periacrosomal material). The nucleus is a long cylindrical structure surrounding a PAS-positive rod (extranuclear rod) which ends blindly in its anterior region. The extranuclear rod lies in a lumen bounded by the nuclear envelope. At the base of the nucleus is a centriolar fossa containing a centriole embedded in a fibrous matrix. Extending from the centriole is the axial filament complex, surrounded by nine outer fibers that course through the major portion of the sperm tail. The middle piece is composed of a number of columns of mitochondria which are circumferentially positioned around the anterior region of the sperm tail. The posterior limit of the middle piece is marked by an annulus of electron opaque material. Glycogen particles fill the intracellular space between the plasma membrane and the outer fibers of the sperm tail.