
Abylopsis is a siphonophore genus in the Abylidae. The genus contains bioluminescent species.

Aegina citrea is a genus of hydrozoans in the family Aeginidae.

Aeginura is a genus of hydrozoans in the family Aeginidae.

Aequorea is a genus of pelagic hydrozoans in the family Aequoreidae.

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.

Agalma is a genus of siphonophores in the family Agalmatidae. Siphonophores are colonial hydrozoans that feed on zooplankton.

Anthomastus is a genus of soft corals in the family Alcyoniidae.

Apolemia is a genus of siphonophores. It is the only genus in the monotypic family Apolemiidae.

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.

Campanularia is a genus of hydrozoans, in the family Campanulariidae.

Cavernularia is a genus of marine cnidarians in the family Veretillidae.

Colobonema is a genus of deep-sea hydrozoans.

Crossota is a genus of hydrozoans of the family Rhopalonematidae. The genus comprises five species. Unlike most hydromedusae, these do not have a sessile stage. Rather, they spend their entire lives in the water column as plankton. The genus Crossota is widespread throughout the oceans.

Cunina is a genus of hydrozoan in the Cuninidae. The genus contains bioluminescent species.

Forskalia is a genus of siphonophores. It is the only genus in the monotypic family Forskaliidae.

The helmet jellyfish is a luminescent, red-colored jellyfish of the deep sea, belonging to the order Coronatae of the phylum Cnidaria. It is the only species in the monotypic genus Periphylla.

Isidella is a genus of deep-sea bamboo coral in the family Isididae.

Keratoisis is a genus of deep-sea bamboo coral in the family Isididae, containing the following species:

Lepidisis is a genus of deep-sea bamboo coral in the family Isididae. It contains the following species:

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.

Parazoanthus is a genus of anemone-like anthozoans in the order Zoantharia.

Pelagia is a genus of jellyfishes in the family Pelagiidae. It is currently considered as monotypic with one species, Pelagia noctiluca (Forsskål, 1775).

Pennatula is a genus in the family Pennatulidae. The genus contains bioluminescent species.

Poralia is a genus of jellyfish in the family Ulmaridae. It is a monotypic genus containing a single species, Poralia rufescens. This jellyfish is pelagic, and is found in deep water in most of the world's oceans.

Praya is a genus of marine invertebrates in the order Siphonophora. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. It contains the following species:Praya dubia (Quoy & Gaimard in de Blainville, 1830) Praya reticulata (Bigelow, 1911)

The Praya dubia, or giant siphonophore, is an invertebrate which lives in the deep sea at 700 m (2,300 ft) to 1,000 m (3,300 ft) below sea level. It has been found off the coasts around the world, from Iceland in the North Atlantic, to Chile in the South Pacific.

Renilla is a genus of sea pen. It is the only genus within the monotypic family Renillidae.

Renilla koellikeri is a species of sea pen that has been reported from the southern coast of California, including Santa Barbara, California.

Renilla muelleri is a species of sea pansy. It has been reported from the Gulf Coast of the United States, notably the Florida panhandle, but is also reported from the eastern coast of South America. It is thought to be a euryhaline littoral species, found to a depth of up to 150 meters.

The sea pansy, Renilla reniformis, is a species of colonial cnidarian in the family Renillidae, part of an octocoral subclass of Anthozoa that inhabit an expansive range of environments. It is native to warm continental shelf waters of the Western Hemisphere. It is frequently found washed ashore on North East Florida beaches following northeasterly winds or rough surf conditions. It also can often be found living intertidally completely buried in the sand. Its predator is the striped sea slug, Armina tigrina.

Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described species, around 200 are valid. Sea pens have a cosmopolitan distribution, being found in tropical and temperate waters worldwide, as well as from the intertidal to depths of more than 6100m. Sea pens are grouped with the octocorals, together with sea whips or gorgonians.

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.

Umbellula is a genus of cnidarians in the family Umbellulidae. The genus contains bioluminescent species.

Veretillum is a genus in the family Veretillidae. The genus contains bioluminescent species.

Virgularia is a genus of sea pen in the family Virgulariidae.