HAPLOSPORIDIUM SP. (HAPLOSPORIDIA) IN HATCHERY-REARED PEARL OYSTERS, PINCTADA-MAXIMA (JAMESON, 1901), IN NORTH-WESTERN AUSTRALIA

A species of Haplosporidium is described from 6 of 105 pearl oyster (P inctada maxima) spat from a hatchery at Carnarvon in north Western Aus tralia. Presporulation and sporulation stages occurred in the connecti ve tissue surrounding the digestive gland and were common in mantle co nnective tissue, but only light to moderate infections were observed i n the heart, gills, foot, and adductor muscle. No stages were observed in epithelia, and the gut and diverticulae remained intact. Ultrastru cturally, sporoblasts were binucleate with the two nuclei either close ly apposed to form a diplokaryon or separated, with the cytoplasm cont aining round to pyriform haplosporosomes. In spores the sporoplasm con tained a basal, or sometimes equatorial, nucleus, dense ovoid vesicles that appeared to develop to ovoid haplosporosomes with an internal ax ehead-shaped membrane, and spherical haplosporosomes. Apparently senes cent spores with a dense content were also present and they, and norma l spores, were ornamented with filaments placing the parasite in the g enus Haplosporidium. (C) 1998 Academic Press.