Scyphozoa
Encyclopedia
Scyphozoa is a class within the phylum
Cnidaria
, sometimes referred to as the "true jellyfish
".
The class name Scyphozoa comes from the Greek
word skyphos
(σκύφος), denoting a kind of drinking cup and alluding to the cup shape of the organism.
Scyphozoans range in geological time from the Ediacaran
period through the Recent
.
or jellyfish
form, which is most evident in the warm summer months, and an inconspicuous, but longer-lived bottom-dwelling polyp, which seasonally gives rise to new medusae. Most of the large, often colorful, and conspicuous jellyfish found in coastal waters throughout the world are Scyphozoa. They typically range from 2 to 40 cm (0.78740157480315 to 15.7 in) in diameter, but the largest species, Cyanea capillata can reach 2 metres (6.6 ft) across. Scyphomedusae are found throughout the world's oceans, from the surface to great depths; no Scyphozoa occur in freshwater (or on land).
As medusae, they eat a variety of crustaceans and fish, which they capture using stinging cells called nematocysts. The nematocysts are located throughout the tentacles that radiate downward from the edge of the umbrella dome, and also cover the four or eight oral arms that hang down from the central mouth. Some species, however, are instead filter feeders, using the tentacles to strain plankton
from the water.
, which provides the same structural integrity as a skeleton. The mesoglea includes mobile amoeboid cells originating from the epidermis.
Scyphozoans have no durable hard parts, including no head, no skeleton and no specialized organs for respiration or excretion. Marine jellyfish can consist of as much as 99% water and therefore are rarely found in fossil form.
Unlike the hydrozoan jellyfish, hydromedusae, scyphomedusae lack a velum
, which is a circular membrane beneath the umbrella that helps propels the (usually smaller) hydromedusae through the water. However, a ring of muscle fibres is present within the mesoglea around the rim of the dome, and the jellyfish swims by alternately contracting and relaxing these muscles. The periodic contracting and relaxing propels the jellyfish through the water, allowing it to escape predation or catch its prey.
The mouth opens into a central stomach, from which four interconnected diverticula
radiate outwards. In many species, this is further elaborated by a system of radial canals, with or without an additional ring canal towards the edge of the dome. Some genera, such as Cassiopea
, even have additional, smaller mouths in the oral arms. The lining of the digestive system includes further stinging nematocysts, along with cells that secrete digestive enzyme
s.
The nervous system usually consists of a distributed net of cells, although some species possess more organised nerve rings. In species lacking nerve rings, the nerve cells are instead concentrated into small structures called rhopallia. There are between four and sixteen of these small lobes arranged around the rim of the umbrella, where they coordinate the muscular action allowing the animal to move. Each rhopallium is typically associated with a pair of sensory pits, a statocyst
, and sometimes a pigment-cup ocellus
.
s are located in the stomach lining, and the mature gamete
s are expelled through the mouth. After fertilization, some species brood their young in pouches on the oral arms, but they are more commonally planktonic.
The fertilized egg produces a planula
larva which, in most species, quickly attaches itself to the sea bottom. The larva develops into the hydroid stage of the life-cycle, a tiny sessile polyp called a scyphistoma. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa, or budding several medusae off from its upper surface. The medusae are initially microscopic, and may take years to reach sexual maturity.
, in the order Semaeostomeae, and the enormous Nemopilema nomurai, in the Order Rhizosomeae, found between Japan and China and which in some years causes major fisheries disruptions.
Most of the jellyfish that are fished commercially for food are scyphomedusae in the order Rhizostomeae. Most rhizostome jellyfish live in warm water.
.
Class Scyphozoa
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
, sometimes referred to as the "true jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
".
The class name Scyphozoa comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word skyphos
Skyphos
In classifying the pottery of Ancient Greece, a skyphos is a two-handled deep wine-cup on a low flanged base or none. The handles may be horizontal ear-shaped thumbholds that project from the rim , or they may be loop handles at the rim or that stand away from the lower part of the body...
(σκύφος), denoting a kind of drinking cup and alluding to the cup shape of the organism.
Scyphozoans range in geological time from the Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
period through the Recent
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
.
Biology
Most species of Scyphozoa have two life history phases, including the planktonic medusaMedusa (biology)
In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below...
or jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
form, which is most evident in the warm summer months, and an inconspicuous, but longer-lived bottom-dwelling polyp, which seasonally gives rise to new medusae. Most of the large, often colorful, and conspicuous jellyfish found in coastal waters throughout the world are Scyphozoa. They typically range from 2 to 40 cm (0.78740157480315 to 15.7 in) in diameter, but the largest species, Cyanea capillata can reach 2 metres (6.6 ft) across. Scyphomedusae are found throughout the world's oceans, from the surface to great depths; no Scyphozoa occur in freshwater (or on land).
As medusae, they eat a variety of crustaceans and fish, which they capture using stinging cells called nematocysts. The nematocysts are located throughout the tentacles that radiate downward from the edge of the umbrella dome, and also cover the four or eight oral arms that hang down from the central mouth. Some species, however, are instead filter feeders, using the tentacles to strain plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
from the water.
Anatomy
Scyphozoans usually display a four-part symmetry and have an internal gelatinous material called mesogleaMesoglea
Mesoglea is the translucent, inert, jelly-like substance that makes up most of the bodies of jellyfish, comb jellies and certain primitive sea creatures in the phyla Cnidaria and Ctenophora. It acts as the creatures' structural support in water, as they lack bones or cartilage, endo- or...
, which provides the same structural integrity as a skeleton. The mesoglea includes mobile amoeboid cells originating from the epidermis.
Scyphozoans have no durable hard parts, including no head, no skeleton and no specialized organs for respiration or excretion. Marine jellyfish can consist of as much as 99% water and therefore are rarely found in fossil form.
Unlike the hydrozoan jellyfish, hydromedusae, scyphomedusae lack a velum
Velum
Velum may refer to:* Superior medullary velum, part of the nervous system that stretches between parts of the brain* Veil , the veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and torn by growth...
, which is a circular membrane beneath the umbrella that helps propels the (usually smaller) hydromedusae through the water. However, a ring of muscle fibres is present within the mesoglea around the rim of the dome, and the jellyfish swims by alternately contracting and relaxing these muscles. The periodic contracting and relaxing propels the jellyfish through the water, allowing it to escape predation or catch its prey.
The mouth opens into a central stomach, from which four interconnected diverticula
Diverticulum
A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....
radiate outwards. In many species, this is further elaborated by a system of radial canals, with or without an additional ring canal towards the edge of the dome. Some genera, such as Cassiopea
Cassiopea
The Cassiopea jellyfish belongs to the Order Rhizostomeae and mostly lives in sandy areas and seagrass beds. The Cassiopea jellyfish is also called "Upside Down Jellyfish", because it lies on its back, so that the bell touches the ground. In this position it resembles a sea anemone...
, even have additional, smaller mouths in the oral arms. The lining of the digestive system includes further stinging nematocysts, along with cells that secrete digestive enzyme
Digestive enzyme
'Digestive enzymes' are enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tract of animals where they aid in the digestion of food as well as inside the cells,...
s.
The nervous system usually consists of a distributed net of cells, although some species possess more organised nerve rings. In species lacking nerve rings, the nerve cells are instead concentrated into small structures called rhopallia. There are between four and sixteen of these small lobes arranged around the rim of the umbrella, where they coordinate the muscular action allowing the animal to move. Each rhopallium is typically associated with a pair of sensory pits, a statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...
, and sometimes a pigment-cup ocellus
Ocellus
A simple eye refers to a type of eye design or optical arrangement that contains a single lens which detect light. A "simple eye" is so-called in distinction from a multi-lensed "compound eye", and is not necessarily at all simple in the usual sense of the word...
.
Reproduction
Most species appear to be gonochorists, with separate male and female individuals. The gonadGonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s are located in the stomach lining, and the mature gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s are expelled through the mouth. After fertilization, some species brood their young in pouches on the oral arms, but they are more commonally planktonic.
The fertilized egg produces a planula
Planula
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. The planula forms from the fertilized egg of a medusa, as the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans...
larva which, in most species, quickly attaches itself to the sea bottom. The larva develops into the hydroid stage of the life-cycle, a tiny sessile polyp called a scyphistoma. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa, or budding several medusae off from its upper surface. The medusae are initially microscopic, and may take years to reach sexual maturity.
Commercial importance
Scyphozoa includes the moon jelly Aurelia auritaAurelia aurita
Aurelia aurita is one of a group of more than ten morphologically nearly identical jellyfish species in the genus Aurelia...
, in the order Semaeostomeae, and the enormous Nemopilema nomurai, in the Order Rhizosomeae, found between Japan and China and which in some years causes major fisheries disruptions.
Most of the jellyfish that are fished commercially for food are scyphomedusae in the order Rhizostomeae. Most rhizostome jellyfish live in warm water.
In popular culture
Scyphozoa is the name of a fictional monster in the animated series Code LyokoCode Lyoko
Code Lyoko is a French animated television series created by Thomas Romain and Tania Palumbo. The series centers on boarding school students Jeremie, Ulrich, Yumi, and Odd who travel to the virtual world of Lyoko to fight against multi-agent computer program XANA with Aelita, a being originally...
.
Taxonomy
Although the Scyphozoa was formerly thought to include the animals now referred to the classes Cubozoa and Staurozoa, it is now thought to include just three orders:Class Scyphozoa
- Order Coronatae
- Family Atollidae
- Family Atorellidae
- Family NausithoidaeNausithoidaeNausithoidae is a family of jellyfish.-Nausithoe:Contains the following species:* Nausithoe albatrossi* Nausithoe atlantica* Nausithoe aurea* Nausithoe challengeri* Nausithoe clausi* Nausithoe eumedusoides...
- Family Paraphyllinidae
- Family PeriphyllidaePeriphyllidaePeriphyllidae is a family of jellyfish, a type of animal.-Pericolpa:Contains the following species:* Pericolpa campana* Pericolpa quadrigata-Periphyllopsis:Contains the following species:* Periphyllopsis braueri...
- Order SemaeostomeaeSemaeostomeaeSemaeostomeae is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbranched pouches radiating outwards from the central stomach; there is no ring...
- Family CyaneidaeCyaneidaeCyaneidae is a family of jellyfish. There are 14 species in this family. They are most commonly found in the southern part of the Atlantic Ocean.-Species:*Cyanea**Cyanea annasethe Haeckel 1880**Cyanea annaskala von Lendenfeld,1884...
- Family PelagiidaePelagiidaePelagiidae is a family of jellyfish. There are 15 species in this family.-Genera:*Chrysaora**Chrysaora achlyos Martin, Gershwin, Burnett, Cargo & Bloom 1997**Chrysaora africana **Chrysaora blossevillei Lesson 1830...
- Family UlmaridaeUlmaridaeUlmaridae is a family of jellyfish.-Genera:*Aurelia *Aurosa*Deepstaria*Diplulmaris*Discomedusa*Floresca*Parumbrosa*Phacellophora - Phacellophora camtschatica*Poralia...
- Family Cyaneidae
- Order Rhizostomeae
- Family Archirhizidae
- Family Cassiopeidae
- Family CatostylidaeCatostylidaeCatostylidae is a family of small jellyfish. Members of this family are characterized by their thick, sausage-like oral arms.-Description:Members of the Catostylidae family are small marine jellyfish with domed bells. The eight short oral arms are broad and three-sided...
- Family CepheidaeCepheidaeCepheidae is a family of jellyfish....
- Family Lobonematidae
- Family Lychnorhizidae
- Family Mastigiidae
- Family Rhizostomatidae
- Family StomolophidaeStomolophidaeStopmolophidae is a family of jellyfish.-Species:*Nemopilema nomurai - Nomura's jellyfish*Stomolophus meleagris - the cannonball or cabbage head jellyfish...
- Subclass DiscomedusaeDiscomedusaeDiscomedusae is a taxonomic group of jellyfish....