First report on histology and ultrastructure of an intrahemocytic paramyxean parasite (IPP) from tunicate Halocynthia roretzi in Korea

In 2004, epizootiological studies were conducted on mass mortalities of tunicates Halocynthia roretzi in Goje, Korea. The clinical characteristics of infected H. roretzi were weakness of the tunic, loss of elasticity, and finally death involving a rupture of the tunic. Histological studies revealed severe hemocyte infiltration in the connective tissue surrounding the intestine and mantle of infected H. roretzi. Hypertrophied eosinophilic hemocytes containing several cytoplasmic vacuoles were observed in the connective tissue surrounding the intestine, gill and mantle. Ultrastructural examination revealed the presence of a parasite in the cytoplasm of hemocytes. Secondary cells were observed in the primary cell of the parasite. Spore formation within primary cells suggests that the parasite may be an intrahemocytic paramyxean parasite (IPP) and may cause mass mortality of H. roretzi.