Among mollusc pathogens, paramyxeans are an important group of protistan parasites belonging to the genera Marteilia and Marteilioides. Marteilia refringens and M. sydneyi are of particular concern given their potential impact on mollusc aquaculture world-wide. Aber disease and QX disease are currently listed by the OIE, the World Organisation for Animal Health. After more than thirty years of existence in the scientific literature, these organisms still pose questions and research challenges to investigators. This paper reviews current knowledge of the group and key references. The review was focused on taxonomy, epidemiology, pathology and potential control methods for these organisms in order to enhance understanding of paramyxean infection issues in mollusc aquaculture.