Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic organisms that are relatively simple in structure.
Aequorea victoria, also sometimes called the crystal jelly, is a bioluminescent hydrozoan jellyfish, or hydromedusa, that is found off the west coast of North America.
Gonionemus is a genus of hydrozoans that uses adhesive discs near the middle of each tentacle to attach to eelgrass, sea lettuce, or various types of algae instead of swimming. They are small and hard to see when hanging onto swaying seaweed. Nevertheless, they are capable of swimming when necessary. The bell is transparent, revealing the four orange to yellowish-tan gonads that lie along most of the length of the four radial canals. The pale yellow manubrium has four short, frilly lips. Up to 80 tentacles line the bell margin, with about an equal number of statocysts. Copepods are a favored prey.
Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity.
Atolla 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.
Clytia gregaria, sometimes referred to as the gregarious jellyfish, is a small species of hydrozoan in the family Campanulariidae. It is one of the most abundant hydrzoans of the Pacific Northwest, particularly during late spring and summer.
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids which are similar enough to have always been considered closely related, and the very apomorphic Siphonophora which were placed outside the "Hydroida". Given that there are no firm rules for synonymy for high-ranked taxa, alternative names like Leptomedusa, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for Leptothecata.
Cladonematidae is a small family of anthomedusan hydrozoans. They have stolonal hydroid colonies, and their medusae are benthic and can crawl across the sediment; in many species they have lost the ability to swim however.
Lovenellidae is a family of hydrozoans. Their hydroids live together in upright stolonal or sympodial colonies, and their gonophores are pedunculate free-roaming medusae. The relationships of this fairly small but distinctive radiation to other members of the order Leptothecata are not well understood at present.
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.
Bougainvilliidae is a family of marine hydroids in the class Hydrozoa. Members of the family are found worldwide. There are sixteen accepted genera and about ninety-three species.
Aeginidae is a family of hydrozoans in the order Narcomedusae. The family comprises 6 genera and 8 species.
Cuninidae is a family of hydrozoans in the order Narcomedusae. They have dome-shaped bells and tentacles set above the undulating margin of the bell. Their gastric pouches contain the gonads situated in line with the tentacles, the number of pouches being the same as the number of tentacles. The pouches do not extend below the points of origin of the primary tentacles. Members of some genera have a peripheral canal system and others do not. No radial canals or secondary tentacles are present.
Solmarisidae is a family of hydrozoans in the order Narcomedusae. The name is sometimes spelled "Solmaridae".
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.
Vallentinia gabriellae, the hitch-hiking jellyfish, is a species of small, inconspicuous hydrozoan in the family Olindiidae. It is endemic to a few isolated parts of the western Atlantic Ocean. It is elusive in the wild but sometimes makes its appearance unexpectedly in seawater cultures of other organisms in the laboratory.
Liriope is a genus of hydrozoan in the family Geryoniidae. It contains only one species, Liriope tetraphylla.
Chironex yamaguchii, commonly known as habu-kurage in Japanese and as "hub jellyfish" due to erroneous machine translations, is a species of box jellyfish found in coastal waters around Japan, on Okinawa and the Ryukyu Islands, and in the Philippines. It is highly venomous.
Coronamedusae is a subclass of jellyfish in the class Scyphozoa. It is the sister taxon of Discomedusae and contains about 50 named species, all included in the order Coronatae. Jellyfish in this subclass are either small medusae living in shallow marine environments, or large medusae living in the deep sea.
