Observations on an apicomplexan microparasite from the pericardic body of Ciona intestinalis L. (Protochordata)

Specimens of the ascidia Ciona intestinalis L. collected in the Gulf of Nap les showed the occurrence within the pericardic body of a microorganism cha racterized by sporogonial plasmodia and complex sporulation stages. An ultr astructural study revealed several sporonts and plasmodia. The latter showe d asynchronous merogonic stages, characterized by merozoites budding at the ir periphery. These stages were abundant and aggregated at the periphery of the pericardic body among haematic cells, cell debris and other host degen erative material. The merogonic plasmodia had a coccidian-like structure an d were the most frequent stages observed in the C. intestinalis pericardic bodies. The microorganism was considered as parasitic and represents a poss ible re-discovery of Cardiosporidium cionae, a sporozoan described early th is century from the same host. Infection by the microparasite appeared impl icated in the origin of the pericardic body, considered as an host response to infection.