Cubomedusa

Cubomedusa is described in almost all tropical and subtropical waters with oceanic salinity . Two species - Carybdea marsupialis and Carybdea rastoni are also noted in the temperate seas.

The body of the cubipolyp is in the form of a cone or a bottle . The sole is located in the peridermal calyx attached to the substrate. On the opposite sole of the end of the body at the top of the mouth cone is the mouth opening . It leads into a blindly closed digestive cavity. In cubipolyps, the intestinal cavity, unlike the polyps of other cortex, is not divided by septa into pockets and, therefore, has the shape of a bag . Around the mouth cone is a corolla of a small number (less than 10) of tentacles . Their location does not demonstrate strict radial symmetry .

The cubipolyps formed during budding of other cubipolyps are able to crawl along the substrate for some time, however, they soon secrete a peridermal calyx and switch to a sedentary lifestyle. Before the formation of cubomedusa, even before separation from the substrate, the cubipolypus undergoes significant rearrangements, which consist in the formation of organs characteristic of jellyfish.

Cubomedus can be easily distinguished from representatives of other classes bowing in the shape of a bell, which has a rectangular shape in cross section. The subumbrellar (located inside the bell) space is limited by the muscular fold of the bell edge ( velarium ). Reactive movement of jellyfish is carried out by reducing the musculature of the bell, as a result of which a powerful jet of water is thrown from the subumbrellar space, pushing the jellyfish in the opposite direction. Reductions in velarium allow not only to reduce the diameter of the outlet opening, increasing the strength of the jet stream, but also - with asymmetric reduction - to change the direction of the stream, thereby determining the direction in which the jellyfish will move ^[3] .

The bases of the tentacles are located at the four corners of the bell, each of which leaves one (in the Carybdeidae family) or several (in the Chirodropidae family) tentacles . The tentacle-covering epidermis contains batteries of stinging cells with which cubomedusae kill their victims. The tentacles of the jellyfish move the victims into the subumbellar space, where the oral stalk ( manubrium ) is located, at the end of which the mouth opening opens. Typically, the length of the manubrium is approximately equal to the height of the bell, so that the mouth is located at the level of its edge.

One type of cubomedusa, , has four attachment fields on the outer surface of the bell, which can be glued to various bottom substrates ^[4] .

Nervous system and sensory organs

The nervous system of cube jellyfish is noticeably more perfect in comparison with other bowing jellyfish. It is based on the diffuse nerve plexus ( nerve plexus ) and the nerve ring located along the edge of the bell.

Between the bases of the tentacles there are sensory structures covered with folds - ropalia . Each ropalia includes an organ of balance and six eyes : four simple (in the form of a groove or a glass) and two very complex. The latter consist of a cornea, lens and retina. Recent studies have found proteins that are sensitive to the light of the blue, green, and ultraviolet parts of the spectrum and resemble vertebral rhodopsins and opsins in the composition of the retina cells of cubomedusa ^[5] . Processing of optical images appears to occur in the nerve ring, the processes of which are suitable for ropalia.

Jellyfish of this group are usually found in shallow water with a sandy bottom. During the day, they are usually near the bottom, and at night they move to the surface of the water. Observations under natural conditions are hindered by the fact that as the diver approaches, the cubomedusae swim away quickly. Cubomedusa are active swimmers and are able to move at speeds up to 6 meters per minute. Some representatives have a positive phototaxis : they move directionally toward the light source.

Although cubo-jellyfish are active during any time of the day, they feed mainly in the evening twilight and at night. Unlike most other coelenterates, vision plays a large role in the nutrition process. Eating behavior in different species varies slightly. Captured by tentacles and affected by stinging cells, prey is reduced by the contraction of tentacles to the mouth. After this, the jellyfish is located vertically in the water (with the mouth up or down) and absorbs food.

Cubomedusa is an important link in the food chain of coastal waters, where they act as predators. They feed mainly on small fish and crustaceans. Polychaetes , bristle-maxillary and other invertebrates can also be victims.

Until the seventies of the XX century, researchers dealt mainly with the jellyfish stage, and the life cycle of cubomedusa remained unknown. The German researcher Bernard Werner was able to reconstruct it for the first time in 1971 .

Like other members of the Medusozoa group, the life cycle of cubomedusa includes the stages of polyp and jellyfish. A single polyp is attached to the bottom and is able to reproduce asexually ( budding ). In the future, he undergoes metamorphosis : after a series of morphological changes, most of the polyp separates and passes to life in the water column, becoming a jellyfish. The part remaining at the bottom dies after some time.

Jellyfish can reproduce sexually . As a rule, fertilization in cubomedusa is external. There are, however, a number of exceptions. For example, males of Carybdea sivickisi secrete and transmit to the females spermatophores ( sperm packets), which are stored in the intestinal cavity of the latter until fertilization . Females of another species ( Carybdea rastoni ) actively collect strands of sperm that males secrete. A free-floating ciliary larva ( planula ) develops from an egg , which settles to the bottom and turns into a polyp.

There are two interpretations of such a life cycle. On the one hand, the formation of only one jellyfish from a polyp can be considered as a metamorphosis. In this case, it turns out that jellyfish and polyp are two stages of ontogenesis of one individual. The second interpretation suggests that the jellyfish is formed during a special form of reproduction - monodisk strobilization , similar to polydisk strobilization of the polyp during the production of jellyfish in scyphoid .

Evidence of the dangers of cubomedusas for humans are special nets that are pulled along the beaches in northern Queensland ( Australia ) to protect against them. Although fatalities occur due to burns from Chironex fleckeri cubo-jellyfish almost every year in Australia, the effects of human interactions with them may vary.

So, the Irukanji jellyfish ( Carukia barnesi ) is the cause of the “ Irukanji syndrome ”, which is expressed in severe pain in the back and stomach, very severe headache , increased local sweating and vomiting, as well as problems with urination. There is an antidote that helps with both Chironex fleckeri burns and burns caused by Carukia barnesi . Acetic acid can also prevent the activation of nematocysts of these jellyfish, which have not yet been stung - while, with other jellyfish, vinegar, on the contrary, facilitates the activation of nematocysts.

Before the reconstruction of the life cycle, cubomedusae were included in the class of scyphoid in the rank of detachment. Modern ideas about the relationship of this group with other contenders differ. As a rule, in the literature, cube jellyfish are mentioned in the rank of a class with an unclear systematic position. However, the results of some studies continue to indicate that Cubozoa is a sister or even a daughter taxon in relation to the class of Scyphoid ^[6] .

As of 2019, the group describes two orders, eight families and about 66 species ^[1] .

• Order Gegenbaur 1857
  • Family Gegenbaur 1857
  • Family Haeckel 1880
  • Family Conant 1897
  • Family Gershwin 2005
  • Family Bentlage, Cartwright, Yanagihara, Lewis, Richards & Collins 2010
• Order Haeckel 1880
  • Family Haeckel 1880
  • Family Thiel 1936
  • Family Chiropsellidae Toshino, Miyake & Shibata 2015

Only one fossil species that is reliably related to cubomedusa is described — Anthracomedusa turnbulli from Paleozoic sediments near Chicago ( Illinois , USA ) ^[7] . This fossil jellyfish lived 323-290 million years ago, had a square dome in the context and collected in bundles of tentacles. Researchers attributed it to the Chirodropidae family.

• Plays an important role in the movie " Seven Lives ."

• Zoology of Invertebrates / Ed. W. Westheide and R. Rieger. M.: KMK Scientific Publications, 2008 ISBN 978-5-87317-491-1
• Ruppert E.E., Fox R.S., Barnes R.D. Protists and lower multicellular // Invertebrate Zoology. Functional and Evolutionary Aspects = Invertebrate Zoology: A Functional Evolutionary Approach / Per. from English T. A. Ganf, N. V. Lentsman, E. V. Sabaneeva; under the editorship of A. A. Dobrovolsky and A. I. Granovich. - 7th edition. - M .: Academy, 2008. - T. 1. - 496 p. - 3000 copies. - ISBN 978-5-7695-3493-5 .