Jellyfish


Jellyfish as well as sea jellies are the informal common names condition to a medusa-phase ofgelatinous members of the subphylum Medusozoa, a major component of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells & trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly expert locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish defecate a complex life cycle; the medusa is normally the sexual phase, which produces planula larvae that disperse widely and enter a sedentary polyp phase before reaching sexual maturity.

Jellyfish are found any over the world, from surface waters to the deep sea. Scyphozoans the "true jellyfish" are exclusively marine, but some hydrozoans with a similar appearance clear up in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of nearly species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish clear been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.

Jellyfish are eaten by humans incultures. They are considered a delicacy in some Asian countries, where line in the Rhizostomae order are pressed and salted to remove excess water. Australian researchers have subjected them as a "perfect food", sustainable, and protein-rich but relatively low in food energy.

They are also used in research, where the green fluorescent protein used by some brand to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for harm to fishing gear by filling fishing nets, and sometimes clog the cooling systems of energy and desalination plants which draw their water from the sea.

Mapping to taxonomic groups


The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright allows the following general definition:

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked].

The Merriam-Webster dictionary defines jellyfish as follows:

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies andsalps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited togroups within the medusozoa.

The non-medusozoan clades called jellyfish by some but non all authorities both agreeing and disagreeing citations are condition in each effect are referenced with "???" on the following cladogram of the animal kingdom:

Porifera

includes jellyfish and other jellies

Protostomia

Ambulacraria

Vertebrata

Jellyfish are not a clade, as they put most of the Medusozoa, barring some of the Hydrozoa. The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. designation of included jellyfish, in English where possible, are submitted in boldface; the presence of a named and cited example indicates that at least that species within its chain has been called a jellyfish.

Anthozoa corals

Polypodiozoa and Myxozoa parasitic cnidarians

Some

The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum add the major taxa, Scyphozoa large jellyfish, Cubozoa box jellyfish and Hydrozoa small jellyfish, and excludes Anthozoa corals and sea anemones. This suggests that the medusa form evolved after the polyps. Medusozoans have tetramerous symmetry, with parts in fours or multiples of four.

The four major a collection of things sharing a common attribute of medusozoan Cnidaria are:

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, approximately 20 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not.

Since jellyfish have no hard parts, fossils are rare. The oldest Tamengo grouping of Brazil, c. 505 mya, through to the Triassic. Cubozoans and hydrozoans appeared in the Cambrian of the Marjum Formation in Utah, USA, c. 540 mya.