Helicosporidium

To date, there is only one named species of Helicosporidia: Helicosporidium parasiticum. It was initially described and named by Keilin in 1921, who detected this protist in larvae of Dasyhelea obscura Winnertz (Diptera: Ceratopogonidae) collected in England. He examined the new parasite thoroughly and attempted to infer its life history from his observations. He described a vegetative growth characterized by very active multiplications of helicosporidial cells inside the body cavity of the host, and noticed that these “schizogonic multiplications” were followed by the formation of what he called spores. Keilin noted that the spores are very easily recognized; they consist of the assembly, inside an external membrane, of three ovoid cells (named by Keilin “sporozoites”) and one peripheral, spiral, filamentous cell. These features, especially the highly characteristic filamentous cell, have since remained the principal diagnostic for identification of a Helicosporidiumsp. Keilin was...