After being infected by Marteilia, bivalves lose pigmentation in their visceral tissue, and become emaciated (Carrasco, Green, & Itoh, 2015).

In the late 1960s and early 1970s, there was a huge decline in European flat oyster (Ostrea edulis) population in Brittany, France.

Around the same time, Marteilia sydneyi was also found to be causing mortalities in Sydney rock oyster (Saccostrea glomerate) in Australia (Perkins & Wolf, 1976).

There has been some success in breeding strains of Sydney rock oyster that are resistant to Marteilia ('QX disease').

[3] Selective breeding has recently incorporated lines of wild oysters from the Richmond River, an estuary long ago affected by QX disease, which have a naturally developed QX-resistance.

At the gills, it undergoes sporogony where it replicates endogenously, producing secondary cells.