Aequoreidae is a hydrozoa

Hydrozoa

Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...

n family. There are approximately 30 known species found in temperate and tropical marine coastal environments. Aequoreids include Aequorea victoria

Aequorea victoria

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. This species is thought to be synonymous with Aequorea aequorea of Osamu Shimomura, the discoverer of green fluorescent protein . ...

, the organism from which the green fluorescent protein

Green fluorescent protein

The green fluorescent protein is a protein composed of 238 amino acid residues that exhibits bright green fluorescence when exposed to blue light. Although many other marine organisms have similar green fluorescent proteins, GFP traditionally refers to the protein first isolated from the...

 gene was isolated.

Polyps

Only the polyp

Polyp

A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the body...

 stages of Aequorea species have been observed. The colonies are covered with chitin

Chitin

Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

ous periderm and can be either prostrate or erect with weak or sympodial

Sympodial

Sympodial means "with conjoined feet", and in biology is often used to refer to the outward morphology or mode of growth of organisms.-In botany:...

 branching. Young possess with a closing structure called operculum

Operculum (animal)

An operculum is an anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal...

., which consists of several relatively long triangular folds that meet together in the centre when a disturbed polyp contracts. Because the operculum is quite fragile, hydrothecae of old polyps usually have only a small chininous collar remaining. Comparatively large cylindrical are attached to the colony with a thin peduncle. Commonly only one medusa develops in each gonotheca.

Medusae

Mature aequoreid medusae

Medusa (biology)

In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below...

 are diverse in shape, from lens-like to conical, and in size. The smallest, Aequerea parva is only 0.6 cm in diameter, while the largest, Rhacostoma atlanticum, can reach 40 cm in diameter. The medusae of most species are between 5 and 15 cm in diameter.

Genera

Aequoreidae includes the following genera:

• Aequorea Péron et Lesueur, 1810 – ca. 20 valid species;
• Aldersladia Gershwin, 2006 – 1 valid species;
• Gangliostoma Xu, 1983 – 2 valid species;
• Rhacostoma L. Agassiz, 1850 – 1 valid species;
• Zygocanna Haeckel, 1879 – 5 valid species.