Haplosporidium

Haplosporidium is a genus in the order Haplosporida.

They are a group of eukaryotes that are parasites of marine invertebrates, causing multiple disease which has high mortality to its host, including the notorious disease MSX, which caused massive oyster mortalities in Delaware Bay in 1957 and two years later in Chesapeake Bay.

There are four genera under order Haplosporida, according to the Hand book of the Protists(2017), The principal characteristics of this genus are spores with an apical-hinged operculum and a variety of extensions externally (tails, filaments, extensions, wrapping, folds, and epispore extensions) formed by the same material of the spore wall. The number of ornaments is variable according to the different species. The internal uninucleated endosporoplasm contains a spherulosome (structure formerly designated by the name “spherule”), generally located at the apical region of the spore, several haplosporosomes, and mitochondria.