# Aequoreidae

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**Aequoreidae** is a family of [hydrozoans](/source/Hydrozoan), sometimes called the **many-ribbed jellies** or **many-ribbed jellyfish**.[1][2] There are approximately 30 known species found in temperate and tropical marine coastal environments.[3] Aequoreids include *[Aequorea victoria](/source/Aequorea_victoria)*, the organism from which the [green fluorescent protein](/source/Green_fluorescent_protein) gene was isolated.[4]

## Morphology

**Polyps**

Only the [polyp](/source/Polyp_(zoology)) stages of *Aequorea* species have been observed.[5] The colonies are covered with [chitinous](/source/Chitin) periderm and can be either prostrate or erect with weak or [sympodial](/source/Sympodial) branching.[5] Young hydranths possess [hydrothecae](/source/Hydrotheca) with a closing structure called *[operculum](/source/Operculum_(animal))*,[5] which consists of several relatively long triangular folds that meet together in the centre when a disturbed polyp contracts.[5] Because the operculum is quite fragile, hydrothecae of old polyps usually have only a small chitinous collar remaining.[5] Comparatively large cylindrical gonothecae are attached to the colony with a thin peduncle.[5] Commonly only one medusa develops in each gonotheca.[5]

**Medusae**

Mature aequoreid [medusae](/source/Medusa_(biology)) are diverse in shape, from lens-like to conical, and in size.[3] The smallest, *[Aequerea parva](/source/Aequerea_parva)* is only 0.6 cm in diameter, while the largest, *[Rhacostoma atlanticum](/source/Rhacostoma_atlanticum)*, can reach 40 cm in diameter.[3][5] The medusae of most species are between 5 and 15 cm in diameter.[3] They have larger stomachs called manubriums, lack a peduncle,[6][7][8] and lack both lateral and marginal cirri.[8][7] All genera have many radial canals with gonads on them.[8][9] Some species, like *[Aequora pensilis](/source/Aequora_pensilis)* can have more than 100 radial canals. Some differences between genera of Aequoreidae include the existence or absence of subumbrella papillae– *[Aequorea](/source/Aequorea)* have them, while *[Rhacostoma](/source/Rhacostoma)* lack them.[8] *[Zygocanna](/source/Zygocanna)* only sometimes possess subumbrella papillae, they are more so characterized by branched (not simple) radial canals.[8] Some members of *Aequorea* (like *[Aequorea victoria](/source/Aequorea_victoria)*) are fluorescent – they have photogenic organs on the outer margins of their umbrellas on the sides of their tentacles that result in a green bioluminescent reaction.[10]

## Distribution

The *Aequoreidae* Family is widely distributed across the globe, typically residing within the [Atlantic](/source/Atlantic_Ocean), [Pacific](/source/Pacific_Ocean), and [Indian Oceans](/source/Indian_Ocean).[11] They are found to populate both tropical temperate waters, often at depths of 200 to, in some extreme cases, 1000 meters.[11]

In habitats such as the [North Sea](/source/North_Sea), *[Aequorea](/source/Aequorea)* populations heavily depend on the salinity of the waters they are in due to fluctuating hydrological processes influenced plankton variations.[12]

**Seasonality**

*Aequorea* are present year-round, with a start in medusae population in early spring - comprising most of the medusa population in an area.[13] The population peaks in the summer, then shrinks in the late autumn, its population reaching a minimum in March.[14]

## Ecology

**Feeding**

Aequoreids, especially *A. victoria*, are known [ovivores](/source/Egg_predation) and predators of [larval fish](/source/Ichthyoplankton), [copepods](/source/Copepod) and other [zooplankton](/source/Zooplankton), [cnidarians](/source/Cnidaria), and [ctenophores](/source/Ctenophora). They may have a preference for soft prey over [crustacean](/source/Crustacean)-feeding counterparts. They prey on fish when they are young then compete with their older counterparts for zooplankton prey though observations on *Aequorea's* effect on zooplankton stocks may only be small.[13]

**Reproduction**

*Aequorea* contain alternating asexual polyp and sexual medusa stages, with some species containing a benthic [planula](/source/Planula) form.

Medusae engage in [broadcast spawning](/source/Spawning), a form of [external fertilization](/source/External_fertilization) in the water column. 3-16% of *Aequorea* medusae's dry weight is released as eggs during spawning[14] These eggs are then predated upon by other hydrozoan medusae such as *Clytia gregaria.*[15]

Light may have a role as a trigger for sexual activity in *Aequorea* medusae[16] as *A. forskalea* medusae release sperm when exposed to [UV light](/source/Ultraviolet)[13] and *A. victoria* in the [Salish Sea](/source/Salish_Sea) are known to surface at dawn to spawn.[17]

Half of all known Aequoreids have asexually reproducing [hydroids](/source/Hydroid_(zoology)).[5] The increase in population due to these hydroids may have a role in large hydrozoan population increases: blooms.[16][13]

**Death and Parasites**

The Aequoreid life cycle can end during the medusa stage from [hyperiid](/source/Hyperiidae) [amphipods](/source/Amphipoda) parasitizing on their internal sacs: burrowing and eating through them.[17] When this happens in the autumn, the medusa has difficulty regenerating its lost tissue.[13] Species are differentially affected by this though, as *A. forksalea* medusae have low rates of hyperiid infestation.[18] [Flukes](/source/Trematoda) spend part of their life cycle within medusae as [secondary hosts](/source/Host_(biology)). The medusae are then eaten by a definitive host fish.[19]

*A. victoria* is frequently harvested by humans for [aequorin](/source/Aequorin), making humans a major predator of theirs.[17] [Green Fluorescent Protein (GFP)](/source/Green_fluorescent_protein) has also been used in place of aequorin, decreasing its demand.[20] Aequorea species are also bycatch in jellyfish fisheries in [Vietnam](/source/Vietnam).[21]

**Climate Change**

Aequoreids are affected by climate change through the processes of [eutrophication](/source/Eutrophication) and [ocean acidification](/source/Ocean_acidification), which both reduce competition in their habitats.

Eutrophication is driven by changing water composition from modified currents and pollution.[22] Blooms and the conditions therein: low oxygen, low visibility, high prey items favor jellies over fish, whose populations aren’t limited by prey population density.[23][24][25]

Ocean acidification is driven by increasing atmospheric CO2 concentrations. Aequoreidae are more tolerant of lower pH compared to fish.[26]

## Genera

Aequoreidae includes the following genera:[13]

- *[Aequorea](/source/Aequorea)* Péron et Lesueur, 1810 – ca. 20 valid species
- *[Aldersladia](/source/Aldersladia)* Gershwin, 2006 – 1 valid species

Genus *Aldersladia* contains only *[Aldersladia magnificus](/source/Aldersladia_magnificus)*, found in [Australia](/source/Australia) - common in [Darwin Harbour](/source/Darwin_Harbour). It is characterized by having one or a few obvious solid papillae under its radial canals, which are found under its umbrella. It is correlated with female hyperiid amphipod parasites of species *Lestrigonus bengalensis* on its umbrella. It used to be misidentified as *Aequorea pensilis*,[8] as its papillae under its umbrella were previously ignored.[27]

- *[Gangliostoma](/source/Gangliostoma)* Xu, 1983 – 2 valid species

The *[Gangliostoma](/source/Gangliostoma)* genera contains two species: *Gangliostoma dayaensis* and the recently discovered *Gangliostoma guangdongensis*.[28] *G. guangdongensis* contains a marginal more radial canals and tentacles—between 38 to 56 and 90 to 108 respectively—than *G. dayaensis*, which contains only around 33 radial canals and 13 tentacles.[28] *G. dayaensis*, while containing shorter oral lips contains a distinct excretory papillae with 3 rudimentary bulbs and 4 statocysts, contrasting with *G. guangdongensis* complete lack of rudimentary bulbs and excretory papillae and singular statocyst.[28]

- *[Rhacostoma](/source/Rhacostoma)* L. Agassiz, 1850 – 1 valid species

Rhacostoma have papillae underneath their subumbrella, and have a single species in their genera; *[Rhacostoma atlanticum](/source/Rhacostoma_atlanticum)* which is the largest species from the Aequoreidae family, ranging from 300 mm to 400 mm wide.[8] Their stomachs are around one third to a half the size of their body width.[8]

- *[Zygocanna](/source/Zygocanna)* Haeckel, 1879 – 5 valid species

## See also

- *[Aequorea tenuis](/source/Aequorea_tenuis)*
- *[Aequorea victoria](/source/Aequorea_victoria)*

## References

1. ["Many-ribbed Jellies (Family Aequoreidae)"](https://inaturalist.ca/taxa/171652-Aequoreidae). *iNaturalist Canada*

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