Ultrastructure of merogonic development of Haemogregarina (sensu lato) myoxocephali (Apicomplexa: Adeleina) in the marine leech Malmiana scorpii and localization of infective stages in the salivary cells.

The post-sporogonic development of Haemogregarina myoxocephali was examined in Malmiana scorpii for 50 days following the removal of these leeches from their fish host, Myoxocephalus octodecemspinosus. Sporozoites released from intestinal oocysts invaded epithelial cells and transformed into large uninucleate meronts. Following the aggregation of small electron dense vesicles into crystalloid inclusions, 4 elongate merozoites were formed. Merozoites, released into the lumen of the intestine, penetrated through to the blood sinus and were found in the salivary cells of leeches 50 days following removal from fish. Crystalloid bodies, accumulations of dense vesicles, may represent reserve material for rhoptries or micronemes. These data represent the first ultrastructural characterization of the infective stages of a fish haemogregarine. The appropriate generic position for the haemogregarines of fish is discussed in relation to these findings.