Observations on the ultrastructure of Haemogregarina simondi in the marine flatfish Solea solea (L.).

Developing stages of Haemogregarina simondi from the marine fish Solea solea (L.) were examined by electron microscopy. Merozoites lay in a parasitophorous vacuole and were bound by a pellicle of three unit membranes beneath which lay a ring of 45--61 microtubules. The cytoplasm contained 4--6 rhoptries, more than 169 micronemes, several mitochondria, and amylopectin granules. A conoid and one polar ring were observed at the anterior end. Intraleucocytic and intraerythrocytic schizonts with up to eight merozoites were described also. Intraerythrocytic and free gametocytes were characterized by distinct refractile bodies and a pellicle consisting of only two unit membranes. The number of micronemes was in excess of 194. The results were discussed in comparison with other members of the Haemogregarinidae.