Sperm morphology in the black coral Cirrhipathes sp. (Anthozoa, Antipatharia)

Male polyps of the antipatharian Cirrhipathes sp., collected along the coral reef of Siladen Island (Sulawesi, Indonesia), were studied in order to gain an insight into the reproductive biology. Spermatocysts (maximum size 120 mm) are located within the primary gametogenic mesenteries and are separated by mesenteric cell cytoplasmic extensions. Sperm, maturing along radial rows, have a fairly round shape and contain a series of electron-dense vesicles in the apical nuclear region. A single mitochondrion flanks the nucleus. A peculiar cup-like electron-dense body, edged with regularly spaced electron-dense granules, is interposed between the nucleus and the tail, and delimits a central region that includes two centrioles. Cross-sections of the cup-like body reveal that the distal centriole has a pericentriolar system, consisting of nine arms arranged in a radial pattern. Each arm branches into three processes that are connected to the electron-dense granules. Indirect evidence of spawning is derived fromthe accumulation of sperm in the gastric cavity. This process takes place through the lysis of the cells bordering the mesenteries. Intact cells of this bordering layer appear to be involved in the phagocytosis of non-expelled gametes.