WApolemia is a genus of siphonophores. It is the only genus in the monotypic family Apolemiidae.
WAtolla is a genus of crown jellyfish in the order Coronatae. The genus Atolla was originally proposed by Haeckel in 1880 and elevated to the monotypic family level, as Atollidae by Henry Bigelow in 1913. The six known species inhabit the mesopelagic zone. The medusae possess multiple lobes called lappets at the bell margin. Medusae also have eight tentacles, alternating with eight rhopalia, and twice as many lappets occur as tentacles.
WBazinga is a genus of rhizostome jellyfish with only one known species, Bazinga rieki, found off the central eastern coast of Australia.
WCarybdea is a genus of venomous box jellyfish in the family Carybdeidae.
WCassiopea is a genus of true jellyfish and the only members of the family Cassiopeidae. They are found in warmer coastal regions around the world, including shallow mangrove swamps, mudflats, canals, and turtle grass flats in Florida, and the Caribbean and Micronesia. The medusa usually lives upside-down on the bottom, which has earned them the common name. These jellyfish partake in a symbiotic relationship with photosynthetic dinoflagellates and therefore, must lay upside-down in areas with sufficient light penetration to fuel their energy source. Where found, there may be numerous individuals with varying shades of white, blue, green and brown.
WCordylophora is the sole genus of hydrozoans in the monotypic family Cordylophoridae.
WCraterolophus is a genus of jellyfish. It is the only genus in the monotypic family Craterolophidae. Species of this genus are characterized by the absence of primary tentacles as well as the absence of longitudinal muscles running along the peduncle.
WDendrogramma enigmatica is a species of siphonophore, the only species of its genus. It has been first described in 2014 on the basis of its morphology from a collection of specimens gathered in 1986. As its taxonomic affinity among animals was unclear, it has been further identified in 2016 as a siphonophore by barcoding and phylogenomics from RNA material from new specimens. The specimens are presumed to represent parts (bracts) of the entire siphonophore, which has not been identified yet.
WForskalia is a genus of siphonophores. It is the only genus in the monotypic family Forskaliidae.
WCalvadosia is a genus of stalked jellyfish in the order Stauromedusae. It is the only genus in the monotypic family Kishinouyeidae.
WKudoa 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.
WLipkea is a genus of stalked jellyfish. It is the only genus in the monotypic family Lipkeidae. Lipkea species lack tentacles at the end of their bell.
WFire corals (Millepora) are a genus of colonial marine organisms that exhibit physical characteristics similar to that of coral. The name coral is somewhat misleading, as fire corals are not true corals but are instead more closely related to Hydra and other hydrozoans, making them hydrocorals. They make up the only genus in the monotypic family Milleporidae.
WMonobrachium is a genus of hydroids. These marine cnidarians form the only genus of the monotypic family Monobrachiidae.
WPhacellophora camtschatica, commonly known as the fried egg jellyfish or egg-yolk jellyfish, is a very large jellyfish in the family Phacellophoridae. This species can be easily identified by the yellow coloration in the center of its body which closely resembles an egg yolk, hence how it got its common name. Some individuals can have a bell close to 60 cm (2 ft) in diameter, and most individuals have 16 clusters of up to a few dozen tentacles, each up to 6 m (20 ft) long. A smaller jellyfish, Cotylorhiza tuberculata, typically found in warmer water, particularly in the Mediterranean Sea, is also popularly called a fried egg jellyfish. Also, P. camtschatica is sometimes confused with the Lion's mane jellyfish.
WThe Portuguese man o' war, also known as the man-of-war, bluebottle, or floating terror is a marine hydrozoan found in the Atlantic Ocean and Indian Oceans. It is considered to be the same species as the Pacific man o' war, which is found mainly in the Pacific Ocean.
WPlesiastraea is a genus of corals. It is the only genus in the monotypic family Plesiastreidae.
WPolypodium is a genus of parasite attacking the eggs of sturgeon and similar fishes. It is one of the few metazoans (animals) that live inside the cells of other animals.
WSolanderia is the sole genus of hydrozoans in the monotypic family Solanderiidae. They are commonly known as tree hydroids or sea fan hydroids.
WTamoya is a genus of box jellyfish within the monotypic family Tamoyidae. Recently discovered genus Malo was also associated to this family.
WTetraplatia is a genus of hydrozoans in the order Narcomedusae. It is the sole genus in the monotypic family Tetraplatidae.