![]() The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. Polypodiozoa and Myxozoa (parasitic cnidarians) Names of included jellyfish, in English where possible, are shown in boldface the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish. The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa. The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with " ?" on the following cladogram of the animal kingdom:Ĭnidaria (includes jellyfish and other jellies) Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa. Given that jellyfish is a common name, its mapping to biological groups is inexact. The Merriam-Webster dictionary defines jellyfish as follows:Ī 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. Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle staurozoans are the exceptions. The American evolutionary biologist Paulyn Cartwright gives the following general definition: The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa. Mapping to taxonomic groupsĪ purple-striped jellyfish at the Monterey Bay Aquarium Phylogeny Definition Ī group of jellyfish is called a "smack" or a "smuck". Many sources refer to only scyphozoans as "true jellyfish". In scientific literature, "jelly" and "jellyfish" have been used interchangeably. The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either. The name jellyfish, in use since 1796, has traditionally been applied to medusae and all similar animals including the comb jellies ( ctenophores, another phylum). When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. The stinging cells used by jellyfish to subdue their prey can injure humans. They are also used in research, where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms. Australian researchers have described them as a "perfect food", sustainable, and protein-rich but relatively low in food energy. They are considered a delicacy in some Asian countries, where species in the Rhizostomae order are pressed and salted to remove excess water. Jellyfish are eaten by humans in certain cultures. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group. ![]() The medusae of most 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. Large, often colorful, jellyfish are common in coastal zones worldwide. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Jellyfish are found all over the world, from surface waters to the deep sea. Jellyfish have 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. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. The bell can pulsate to provide propulsion for highly efficient locomotion. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Spotted jellies swimming in a Tokyo aquarium ![]()
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