Hydrozoa are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most living in salt water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in fresh water. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
Rhacostoma is a genus of aequoreid hydrozoans. It is monotypic with a single species, Rhacostoma atlanticum. It has been reported from the Atlantic coastline of North America, Colombia, western and central Africa. The polyp stage is unknown.
Solmissus, or dinner plate jellyfish, is a genus of hydrozoans. Its species are unique among cnidarians in that they actively hunt for prey as opposed to passively waiting for plankton to pass by. They are found in the deep waters of Monterey Bay, California. They are most likely to be found in the deep sea, mid water. They grow to be 20 cm (7.9 in) in diameter. These hydrozoans feed on gelatinous zooplankton, including salps and doliolids, ctenophores, jellyfish, and copepods.. However, Solmissus may be limited to feeding on soft-bodied prey by the type of nematocysts on their tentacles (Mills).
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnoblastea and, Anthomedusa,Athecata, Hydromedusa, and Stylasterina. There are about 1,200 species worldwide.
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with usually a gastric pouch above each. There are no bulbs on the tentacles and no radial canals. Narcomedusans are mostly inhabitants of the open sea and deep waters. They can be found in the Mediterranean in large numbers.
Bolinopsidae is a family of ctenophores.
Pandeidae is a family of hydroids in the class Hydrozoa. Like other jellyfish there is usually a mature medusa form which is pelagic and reproduces sexually and a hydroid or polyp form which is often benthic and reproduces asexually by budding.
Aeginidae is a family of hydrozoans in the order Narcomedusae. The family comprises 6 genera and 8 species.
Solmarisidae is a family of hydrozoans in the order Narcomedusae. The name is sometimes spelled "Solmaridae".
Tetraplatia is a genus of hydrozoans in the order Narcomedusae. It is the sole genus in the monotypic family Tetraplatidae.
Limnomedusae is an order of hydrozoans.
Olindiidae is a family of hydrozoans in the order Limnomedusae. They have a polyp phase and a medusa phase. The polyps are generally small (1 mm) and solitary, but a few species are colonial. They have a varying number of tentacles and can reproduce by budding. In the largest species, the medusae can grow to 15 cm (6 in). Centripetal canals may be present or absent and the radial canals are unbranched. The gonads are beside the radial canals, except in Limnocnida, where they are on the manubrium. The fertilised eggs develop into planula larvae which become polyps. These multiply asexually or can bud off medusae. In some species, medusae are only produced when the water temperature exceeds a certain level. Most species are marine, but several can also be found in brackish water and a few, notably Craspedacusta and Limnocnida, are found in fresh water.
Olindias is a genus of hydrozoans in the family Olindiidae.
Carybdea marsupialis, is a venomous species of cnidarian, in the small family Carybdeidae within the class Cubozoa.
The Diphyidae are a family of siphonophores. These are colonial siphonophores with two nectophores arranged one behind the other. The front one includes a somatocyst, while the hind one does not. The somatocyst often contains an oil droplet for buoyancy control. A nectosac in each nectophore allows the organism to swim efficiently.
Filifera is a suborder of hydrozoans in the order Anthoathecata. They are found in marine, brackish and freshwater habitats.
Eirene is a genus of hydrozoans in the family Eirenidae.
Tima is a genus of hydrozoans in the family Eirenidae.
Cunina is a genus of hydrozoan in the Cuninidae. The genus contains bioluminescent species.
