Mollusc culture, particularly the cultivation of pearl oysters, is an important component of the aquaculture industry in Western Australia. As a result, there has been a long-term investment in surveys of commercial mollusc species for potential diseases of concern. A number of pathogens, particularly haplosporidans, identified within wild-stock shellfish have the potential to adversely affect mollusc populations. Others pose risks for translocations associated with aquaculture. The microsporidan Steinhausia mytilovum (Field), found in ova of the blue mussel Mytilus galloprovincialis (Lamarck), poses intriguing questions about the origin and dispersal of its host.