Kudoa
Kudoa is a genus of Myxozoa and the only genus recognized within the monotypic family Kudoidae. There are approximately 100 species of "Kudoa" all of which parasitize on marine and estuarine fish. "Kudoa" are most commonly known and studied for the negative effects the genus has on commercial fishing and aquaculture industries. Description. The genus "Kudoa" is identified by the possession of four or more shell valves composed of a fragile membrane and arranged in a quadrate or stellate pattern. The maximum number of shell valves in any described "Kudoa" species is 13. Each of these valves has a  polar capsule. The genus "Kudoa" was originally part of the genus "Chloromyxum" because of the distribution of their polar capsules, however, it was later determined to be a separate genus. Each "Kudoa" has two sporoplasm cells, one enclosed by the other. Most "Kudoa" are histozoic parasites, with a few species being described as coelzoic. Some taxonomists question whether these coelzoic organisms belong to a separate genus. There are approximately 100 described species of "Kudoa" which can be found in the Atlantic, Pacific, and Indian oceans. Species. The following species are recognized in the genus "Kudoa": Five additional species have been  proposed, but are not yet widely recognized: Development. In Myxozoan development, the Myxosporean life-stage develops inside a fish host, while the Actinosporean life-stage develops in an annelid host. Fully-developed Myxospores are consumed by annelids and reproduce asexually via schzogony in the gut epithelium of worms. Gametes are formed in the gut of the worm and these gametes fuse together to create eight zygotes. The zygotes become spores with three valves, 3 polar capsules, and a sporoplasm that are released in the worm's feces and attach to the surface of a fish host. Once attached to the  fish, the gamete injects the sporoplasm cell into the fish. The sporoplast divides forming a fully-developed Myxosporean. Diet. "Kudoa" parasitize on marine and estuarine fish. "Kudoa" typically feed on the skeletal muscle tissue, although some may feed on other parts of the body such as the central nervous system, heart, intestines, ovaries, or gills. Most "Kudoa" are histozoic parasites, however, a few species are coelzoic. The genus "Kudoa" attack a wide range of hosts, however, individual species only feed on specific hosts. "Kudoa" feed via pinocytosis across the host-parasite membrane. One species of "Kudoa, K. thyrsites," are distributed  worldwide and are believed to have been reported in over 20 different species of fish but it is possible that the species described as "K. thyrsites" is actually multiple different species. Implications for the fishing industry. "Kudoa" are most well-known for the economic loss they cause for the commercial fishing and aquaculture industries. When "Kudoa" attach to hosts, they leave unsightly cysts that lower the price fish can be sold for at market. "Kudoa" also release proteolytic enzymes that degenerate muscle in fish to aid in their own growth and development, further decreasing the fish's value. Some species  in the genus "Kudoa" with the most notable effects of the commercial fishing and aquaculture industries are: "K. musculoliquefaciens" in Broadbill Swordfish ("Xiphias gladius"), "K. thyrsites" in Atlantic Salmon ("Salmo salar"), "K. clupeidae" in Atlantic Herring ("Clupea harengus"), "K. septempunctata" in Olive Flounder ("Paralichthys olivaceus"), "K. thunni" in Yellowfin Tuna ("Thunnus albacares") and "K. paniformis" in Pacific Hake ("Merluccius productus"). Some studies have found evidence to suggest that some species of "Kudoa" are linked to food-borne illness in humans. References. Encyclopedia of Life