Origin of male gametes from choanocytes inSpongia officinalis(Porifera, Demospongiae)

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Abstract
Spermatogenesis in Spongia officinalis takes place within spermatocysts surrounded by follicle cells. Cysts develop asynchronously from choanocyte chambers by transforming choanocytes into gonia. During this process spermatogonia seem to show phagocytic activity by forming pseudopodia surrounding mesohyl bacteria and cytoplasmic vacuoles which contain such microorganisms. Furthermore nuclei shift from the basal zone of the cells to the apical one, while flagella and collars are lost. Thereafter, the nucleus/cytoplasm ratio tends to increase, cytoplasmic inclusions are lost and the flagellum again becomes visible. Primary spermatocytes, identified by the presence of synaptinemal complexes, and the successive stages of spermatogenesis have been followed up to mature spermatozoa. Secondary spermatocytes are often connected by cytoplasmic bridges deriving from incomplete cytodieresis. Such bridges, which are found to connect spermatids too, could play a role in synchronizing sperm maturation.

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