Ultrastructure of the macrogamont of Eimeria funduli, a coccidium parasitizing killifishes

Abstract. The ultrastructurc of the macrogamont of Eimeria funduli was studied in hepatocytcs of the killifish Funldulus grandis and F. similis. The macrogamont developed in a parasitophorous vacuole (PV) that was bounded by two unit membranes probably derived from an envelope of modified host rough cndoplasmic reticulum (RER). The membrane adjacent to the host-cell cytoplasm was lined with ribosomes. whereas the membrane facing the PV was smooth and blebbed into the PV. Intravacuolar tubules were not observed in the PV. The macrogamonts had a single limiting membrane with lew micropores. Developing macrogamonts had abundant RER. few Golgi bodies, and a few small polysaccharide granules. Nuclei of developing macrogamonts had dispersed chromatin and compact nucleoli. Polysaccharide granules in developing and mature macrogamonts were identified with the periodic acid-thiocarbohydrazide-silver proteinate technique. In mature macrogamonts, polysaccharide granules as large as 1 –2 μm in diameter nearly filled the cytoplasm. The cytoplasm contained three kinds of inclusions that were associated with either the RER or Golgi apparatus. Inclusions identified as type I wall-forming (WF) bodies were small, dense, membrane-bound granules that developed from the Golgi apparatus. Inclusions identified as type II WF bodies were usually dense, irregularly shaped bodies that occupied RER cisternae. Some type II WF bodies had a heterogeneous content but most were homogeneous. A third type of inclusion was related to the cytoplasmic aspect of RER cisternae and consisted of tubules and vacuoles enclosed in a membrane.