''Aurelia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

that are commonly called moon jellies, which are in the class

Scyphozoa The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word '' skyphos'' (), denoting a kind of drinking cup and alluding to the ...

. There are currently 25 accepted species and many that are still not formally described. The genus was first described in 1816 by

Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biologi ...

in his book ''Histoire Naturelle des Animaux sans Vertèbres'' (Natural History of Invertebrates). It has been suggested that ''Aurelia'' is the best-studied group of

gelatinous zooplankton Gelatinous zooplankton are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zoopla ...

, with ''

Aurelia aurita ''Aurelia aurita'' (also called the common jellyfish, moon jellyfish, moon jelly or saucer jelly) is a species of the family (biology), family Ulmaridae. All species in the genus are very similar, and it is difficult to identify ''Aurelia (cnida ...

'' the best-studied species in the genus; two other species, '' Aurelia labiata'' and '' Aurelia limbata'' were also traditionally investigated throughout the 20th century. In the early 2000s, studies that considered genetic data showed that diversity in ''Aurelia'' was higher than expected based solely on morphology, so one cannot confidently attribute the results from most of the previous studies to the species named. More recently, studies have highlighted the morphological variability (including the potential for

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

) in this genus, emphasizing the difficulty of identifying

cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

. Species of ''Aurelia'' can be found in the Atlantic, Arctic, Pacific and Indian Oceans, and seem to be more common in

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

regions, such as in the waters off northern China, Japan, Korea, New Zealand, the northeastern and northwestern coasts of the United States, and those of northern Europe. ''Aurelia'' undergoes alternation of generations, whereby the sexually-reproducing pelagic

medusa In Greek mythology, Medusa (; ), also called Gorgo () or the Gorgon, was one of the three Gorgons. Medusa is generally described as a woman with living snakes in place of hair; her appearance was so hideous that anyone who looked upon her wa ...

stage is either male or female, and the benthic polyp stage reproduces asexually. Meanwhile, life cycle reversal, in which polyps are formed directly from juvenile and sexually mature medusae or their fragments, was also observed in '' Aurelia coerulea'' (= ''Aurelia'' sp. 1).

Appearance

The similar appearances of moon jellyfish is what has made them so hard to identify. They tend to have a variety of different sizes, however, they typically range in diameter with an average of wide and in height. The polyps of these jellyfish can grow to tall and their ephyrae have an average diameter of . The adult medusae are typically translucent in color but the color of their gut can change based on what they eat; for example, if they eat crustaceans, they can have a pink or lavender tint to them and if they were to eat brine shrimp, the tint would be more of an orange color. Their polyps usually have around 16 tentacles (although '' Aurelia insularia'' has 27–33 tentacles) which mostly help with feeding.

Anatomy

The medusa stage of ''Aurelia'' is composed of approximately 95% water. The tentacles along the bell of moon jellyfish as well as the oral arms have stinging cells called cnidocytes. The cnidocytes contain a nematocyst, the part of the jelly that actually stings. The adult moon jellyfish has one stomach, usually divided into 4 sections, though there can be varying numbers of sections.

Feeding

The diet of ''Aurelia'' is similar to that of other jellyfish. They primarily feed on zooplankton. They may prey on or compete with commercially important fish and their larvae, as well as cause several issues for trawling boats when large aggregations occur, as they may clog and damage fishing nets as well as force fisherman to relocate.

Characteristics

They are able to sense light and dark and up and down due to

rhopalia Rhopalia (singular: rhopalium) from Ancient Greek ῥόπαλον (''rhópalon'') 'club' are small sensory structures of certain Scyphozoan (true jellyfish) and Cubozoan (box jellyfish) species. Description The structures typically occur in mul ...

around the bell margin. After many tests on frogs, it was determined that ''A. aurita'' has a proteinaceous venom that causes muscle twitching by inducing the irreversible depolarization of the muscle membrane that is believed to be caused by an increase in the membrane's permeability to sodium ions.

Reproduction

The medusa stage of the jellyfish reproduce sexually. The males release strings of sperm and the females ingest them. Once the ciliated larvae develop from the egg, they settle on or near the sea floor and develop into benthic polyps. The polyps then reproduce asexually and bud into ephyrae which later turn into medusae.

References

External links

Photos of Aurelia in NorwayTree of Life: Aurelia aurita life cycleWorld Register of Marine Species: Aurelia auritaScyphozoan Jellyfish
{{Authority control Scyphozoan genera Cnidarians of the Atlantic Ocean Cnidarians of the Pacific Ocean Ulmaridae