Ultrastructure and functional morphology of spermatozoa of Rossia pacifica (Cephalopoda, Decapoda)

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Abstract
The mature spermatozoan of Rossia pacifica consists of acrosome, nucleus, mitochondrial spur, and tail. Anteriorly, the complex acrosome has a cup-shaped depression containing membrane-bound vacuoles. The acrosome is enclosed by a meshwork of longitudinal and circumferential filaments; its invaginated posterior end surrounds juxtanuclear periacrosomal material. The elongated nucleus, of condensed chromatin filaments, encloses lateroposteriorly the proximal and distal centrioles within a centriolar fossa. Mitochondria lie in a separate, spurlike appendage; proximally its lateral margins are continuous with a collarlike annulus. Nine coarse outer fibres surround the 9 + 2 axoneme. They originate from a centriolar ring and diminish in diameter distally. Staining with periodic acid – Schiff demonstrates some glycogen in the mitochondrial spur near its junction with the nucleus.Structural significance and possible functional roles of the various elements are discussed relevant to fertilization. Although this sperm appears intermediate between the more primitive invertebrate sperm type and highly specialized vertebrate sperm, its morphology seems more related to fertilization biology than to phylogenetic position. The singular separateness of areas of energy production and use in R. pacifica sperm and the lengthy energy-transport path may provide unique opportunities for analysis of metabolic processes common to but indecipherable in other sperm.