Description of Nematopsis mytella n. sp. (Apicomplexa), parasite of the mussel Mytella guyanensis (Mytelidae) from the Amazon estuary and description of its oocysts

Abstract

Summary Numerous uninucleated phagocytes with several parasitophorous vacuoles (PV) each containing a single oocyst of an apicomplexan gregarine parasite of the mussel Mytella guyanensis (Mytelidae) from the Amazon estuary were described. The phagocytes were in close contact with the gill tissue. Each phagocyte was surrounded by a thin layer composed of electron-lucent material. The plasmalemma of the phagocyte presented numerous microvilli irregularly projected to the surrounding thin layer. The phagocyte cytoplasm was occupied by large light areas, numerous small vesicles and among them a variable number of PV each containing a single oocyst. The oocysts were 11.5 μm long and 8.2 μm wide and the wall was 0.7 μm thick. The apical zone of the wall contained a circular micropyle covered by an operculum attached to the PV membrane by a dense cord. Externally, the oocyst wall was surrounded by numerous, long and anastomosed microfibrils attached to the wall and connected to the PV membrane. Several dense bodies within the PV were observed. Each oocyst contained a single vermiform uninucleated sporozoite. This gregarine was named Nematopsis mytella n. sp. and the morphological characteristics of its oocysts were described. This parasite became the first record of Nematopsis sp. and the first gregarine from the Amazonian mussel.