Occurrence of somatic cells within the spermatic cysts of demosponges: A discussion of their role

Abstract During ultrastructural studies on the spermatogenesis of two demosponges, Raspaciona aculeata and Petrosia ficiformis , somatic cells were detected within their spermatic cysts. In R. aculeata large, amoeboid somatic cells, presumably derived from follicle cells, were found inside cysts filled with secondary spermatocytes. These cells were actively phagocytosing spermatocytes. Such phagocytosis could be directed to eliminate aberrant spermatogenic cells, maintain appropriate cell number within the cysts, or recapture energetic reserves originally allocated to the reproductive process via phagocytosis of spermatocytes. In P. ficiformis , somatic round cells were observed only after the spawning event, phagocytosing unspawned sperm in nearly emptied spermatic cysts. Unlike in R. aculeata , these cells were more similar to archaeocytes (common cells of the demosponge mesohyl with phagocytic activity) than to follicle cells. Phagocytosis of spermatogenic cells and unspawned spermatozoa by somatic cells from the wall of the testes is a well-known process in vertebrates and many invertebrates. Occurrence of somatic cells in the spermatic cysts of sponges, whose function appears to be partially analogous to that of Sertoli cells, reveals that sponges possess cellular mechanisms to regulate testis functioning that are equivalent to those in higher metazoans.