The Bivalvulida is an order of myxosporean parasites which contains a number of species which cause economically significant losses to aquaculture and fisheries, such as Myxobolus cerebralis and Ceratomyxa shasta. The Myxosporean stages of members of the bivalvulida are characterised by their two spore valves (hence the name), which meet in a "suture line" which encircles the spore. They usually contain 2 polar capsules, but species have been reported which contain either 1 or 4.