Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Cubozoa, and possibly the parasitic Polypodiozoa. Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa (and Polypodiozoa), all are called jellyfish in their free-swimming medusa phase.
Temporal range: Cambrian–Recent
|Pacific sea nettles, Chrysaora fuscescens|
The phylum Cnidaria is widely accepted as being monophyletic and consisting of two clades, Anthozoa and Medusozoa. Anthozoa includes the classes Hexacorallia, the hard corals, and Octocorallia, the soft corals, as well as Ceriantharia, the tube-dwelling anemones. There is strong support for this group having been the first to branch off from the ancestral line.
Medusozoa includes the classes Staurozoa, Cubozoa, Scyphozoa and Hydrozoa, but the relationships between these are unclear. Analysis using ribosomal RNA subunits suggests that within Medusozoa, Staurozoa was the first group to diverge, with Cubozoa and Scyphozoa forming a clade, a sister group to Hydrozoa. Further study involving the order of mitochondrial genes supports this view, and their possession of linear mitochondrial genomes is striking evidence of the monophyly of medusozoans.
The affinities of the class Polypodiozoa, containing the single species Polypodium hydriforme, have long been unclear. This species is an endoparasite of fish eggs and has a peculiar life cycle. It has traditionally been considered to be a cnidarian because of its possession of nematocysts, but molecular studies using 18S rDNA sequences have placed it closer to Myxozoa. Further studies involving 28S rDNA sequences suggest that it is either part of the hydrozoan clade Leptothecata, or a sister taxon to Hydrozoa, and does not group with myxozoans.
Medusozoans differ from anthozoans in having a medusa stage in their life cycle. The basic pattern is medusa (usually the adult or sexual phase), planula larva, polyp, medusa. Symmetry is tetramerous, with parts in fours or multiples of four. The mitochondrial DNA molecules are linear rather than circular as in anthozoans and almost all other animals. The cnidae, the explosive cells characteristic of the Cnidaria and used in prey capture and defence, are of a single type, there being nematocysts but no spirocysts or ptychocysts. In contrast, the anthozoan life cycle involves a planula larva which settles and becomes a sessile polyp, which is the adult or sexual phase.
There is considerable divergence from the basic life cycle pattern among medusozoans.
Scyphozoa is the group commonly known as "true jellyfish" and occur in tropical, temperate and polar seas worldwide. Scyphozoans generally have planula larvae that develop into sessile polyps. These reproduce asexually, producing similar polyps by budding, and then either transform into medusae, or repeatedly bud medusae from their upper surface in a process known as strobilation.
Cubozoa is a group commonly known as box jellyfish, that occur in tropical and warm temperate seas. They have cube-shaped, transparent medusae and are heavily-armed with venomous nematocysts. Cubozoans have planula larvae, which settle and develop into sessile polyps, which subsequently metamorphose into sexual medusae, the oral end of each polyp changing into a medusa which separates and swims away.
Staurozoa is a small group commonly known as stalked jellyfish. The animals remain attached to the substrate by a stalk at the opposite end from the mouth. Staurozoans can be regarded as large polyps that have partially differentiated into sexually mature medusae. These spawn gametes which develop into non-swimming planulae that crawl away to new locations.
Hydrozoa is a large group of solitary and colonial cnidarians from both marine and freshwater environments worldwide. Hydrozoans exhibit the greatest variety of life cycles among medusozoans, with either the polyp or the medusa stage being missing in some groups. In general, medusae are budded laterally from polyps, become mature and spawn, releasing gametes into the water. The planulae may settle to become polyps or continue living in the water column as medusae.
Carukia barnesi is a small and extremely venomous jellyfish found near Australia. Stings can result in Irukandji syndrome, and thus this species is commonly known as Irukandji jellyfish, although this name does not distinguish it from other Irukandji jellyfish such as Malo kingi.
A mature C. barnesi's bell is only 12 by 30 millimetres (0.47 by 1.18 in) in height. It has four contractile tentacles, one extending from each bottom "corner" of its bell, ranging in length from 5 to 50 centimetres (2.0 to 19.7 in).The species was discovered by Dr. Jack Barnes of Cairns, Australia, who, while on an exploration mission aimed at determining the reason for Irukandji syndrome, allowed himself to be stung by the jellyfish, while his 14-year-old son and a lifeguard looked on. The jellyfish was later named after him.Carukia barnesi is a soft-bodied marine organism. This species falls within the Medusozoa subphylum and the Cubozoa class. It is a type of “Box Jellyfish” that is known for producing potent venom and is known for inflicting the Irukandji syndrome.Threat to Humans: The Irukandji syndrome was first discovered after a group of swimmers were stung in the open water near North Queensland, Australia. Victims of the sting reported severe symptoms of muscle aches, back pain, nausea, headaches, chest and abdominal pains, sweating, high blood pressure and difficulty breathing. Intravenous administration of pethidine is used to treat patients with this syndrome.Most reported incidents have been localized to Australia during the warm summer season. Due to the small size of C. barnesi (approximately 20 mm in diameter and 25 mm in depth of the bell), they often go undetected in the open water.Carybdeida
Carybdeida is an order of box jellyfish. There are five families within the order. They are distinguished from other box jellyfish by the presence of unbranched muscular bases at the corners of the cubic umbrella. Most species have four tentacles.Cnidaria
Cnidaria () is a phylum under Kingdom Animalia containing over 11,000 species of animals found exclusively in aquatic (freshwater and marine) environments: they are predominantly marine.
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, sandwiched between two layers of epithelium that are mostly one cell thick.
They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually, with many species having complex life cycles of asexual polyp stages and sexual medusae. Some, however, omit either the polyp or the medusa stage.
Cnidarians were formerly grouped with ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: the almost wholly sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa (jellyfish); Cubozoa (box jellies); and Hydrozoa, a diverse group that includes all the freshwater cnidarians as well as many marine forms, and has both sessile members, such as Hydra, and colonial swimmers, such as the Portuguese Man o' War. Staurozoa have recently been recognised as a class in their own right rather than a sub-group of Scyphozoa, and the parasitic Myxozoa and Polypodiozoa were only firmly recognized as cnidarians in 2007.Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from dinoflagellates, and a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish, turtles, and even other cnidarians. Many scleractinian corals—which form the structural foundation for coral reefs—possess polyps that are filled with symbiotic photo-synthetic zooxanthellae. While reef-forming corals are almost entirely restricted to warm and shallow marine waters, other cnidarians can be found at great depths, in polar regions, and in freshwater.
Recent phylogenetic analyses support monophyly of cnidarians, as well as the position of cnidarians as the sister group of bilaterians. Fossil cnidarians have been found in rocks formed about 580 million years ago, and other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later. However, molecular clock analysis of mitochondrial genes suggests a much older age for the crown group of cnidarians, estimated around 741 million years ago, almost 200 million years before the Cambrian period as well as any fossils.Corynidae
Corynidae is a family of hydrozoans in the order Anthomedusae.Halicreatidae
Halicreatidae is a family of hydrozoans. The family comprises 6 genera and 9 species.Hydractiniidae
Hydractiniidae is a cnidarian family of athecate hydroids.Hydroidolina
Hydroidolina is a subclass of hydrozoans in the phylum Cnidaria. It contains the bulk of the paraphyletic "Hydroida" which were one of the main groupings of the class Hydrozoa in older classifications and were placed at order rank. Hydroidolina also includes, however, the highly advanced colonial jellies of Siphonophora, which were not included in the "Hydroida".Jellyfish
Jellyfish or 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. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are not mobile, being anchored to the seabed by stalks. The bell can pulsate to provide propulsion and highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle; the medusa is normally the sexual phase, the planula larva can disperse widely and is followed by a sedentary polyp phase.
Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast growing, mature within a few months and die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. 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.Jellyfish are eaten by humans in certain cultures, being considered a delicacy in some Asian countries, where species in the Rhizostomae order are pressed and salted to remove excess water. 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. The stinging cells used by jellyfish to subdue their prey can also injure humans. Many thousands of swimmers are stung every year, with effects ranging from mild discomfort to serious injury or even death; small box jellyfish are responsible for many of these deaths. When conditions are favourable, jellyfish can form vast swarms. These 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.List of prehistoric medusozoan genera
This list of prehistoric medusozoan genera is an attempt to create a comprehensive listing of all genera that have ever been included in the subphylum Medusozoa, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that are no longer considered medusozoans.List of types of seafood
The following is a list of types of seafood. Seafood is any form of sea life regarded as food by humans. It prominently includes fish, shellfish, and roe. Shellfish include various species of molluscs, crustaceans, and echinoderms. Historically, sea mammals such as whales and dolphins have been consumed as food, though that happens to a lesser extent in modern times. Edible sea plants, such as some seaweeds and microalgae, are widely eaten as seafood around the world, especially in Asia (see the category of sea vegetables). In North America, although not generally in the United Kingdom, the term "seafood" is extended to fresh water organisms eaten by humans, so any edible aquatic life may be broadly referred to as seafood.Pelagiidae
The Pelagiidae are a family of jellyfish. Members of the family Pelagiidae have no ring canal, and the marginal tentacles arise from umbrella margin.Planula
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. Some groups of Nemerteans too produce larvae that are very similar to the planula.Plumulariidae
Plumulariidae is a family of hydrozoans.Rhopalonematidae
Rhopalonematidae is a family of hydrozoans. The family comprises 15 genera and 36 species.Stauromedusae
Stauromedusae are the stalked jellyfishes. They are the sole living members of the class Staurozoa, and belong to the medusozoa subphylum of Cnidaria. They are unique among medusa jellyfish in that they do not have an alternation of polyp and medusa life cycle phases but are instead interpreted as an attached medusa stage, with a life style more resembling that of polypoid forms. They have a generally trumpet-shaped body, oriented upside-down in comparison with other jellyfish, with the tentacles projecting upwards, and the stalk located in the centre of the umbrella.
Members of this class are commonly found in relatively cold waters, close to the shoreline.
Sexually mature stauromedusae free-spawn eggs or sperm, which fertilize in the sea and form a creeping, unciliated planula larva. The larvae crawl across the sea floor and find a suitable place, attaching themselves typically to rock or algae, where they eventually develop into a new, attached stauromedusa. Unlike most scyphozoan jellyfish that practice strobilation, or the process of dividing themselves into body segments, which become new individuals, nearly all stauromedusae develop directly into the adult form.Staurozoa
Staurozoa is a class of Medusozoa, jellyfishes and hydrozoans. It has one extant order, Stauromedusae (stalked jellyfishes), and one extinct order, Conulatae. The extinct order is largely unknown and described as a possibly cnidarian clade of marine life with shell-like structures, the Conulariida. Staurozoans are small animals (1–4 cm or 0.4–1.6 in) that live in marine environments, usually attached to seaweeds, rocks, or gravel. They have a large antitropical distribution, a majority found in boreal or polar, near-shore, and shallow waters. Few staurozoans are found in warmer tropical and subtropical water environments of the Atlantic, Indian, and Pacific Ocean basins, but most are known from the Northern Hemisphere.Trachylinae
Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae and Trachymedusae. But the Actinulidae, then considered an independent order, and probably also the Limnomedusae which were traditionally placed in the paraphyletic "Hydroida", belong to this group too. It is not entirely clear whether the Limnomedusae and the Trachymedusae as conventionally circumscribed are monophyleticThe freshwater jelly Craspedacusta sowerbyi is a well-known member of the Limnomedusae and might thus belong here.Tripedaliidae
Tripedaliidae is a family of box jellyfish within class Cubozoa.Ulmaridae
The Ulmaridae are a family of jellyfish.
Extant Cnidaria classes