document_title: Cnidaria

question_text: name the two forms of polymorphism in cnidarian

question_tokens: name the two forms of polymorphism in cnidarian

root

text: Cnidaria

text: Distinguishing features[edit]

text: Cnidarians form an animal phylum that are more complex than sponges, about as complex as ctenophores (comb jellies), and less complex than bilaterians, which include almost all other animals. However, both cnidarians and ctenophores are more complex than sponges as they have: cells bound by inter-cell connections and carpet-like basement membranes; muscles; nervous systems; and some have sensory organs. Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are used mainly to capture prey. In some species, cnidocytes can also be used as anchors.[9]

tag: p

text: Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians; more complex animals have three main cell layers and no intermediate jelly-like layer. Hence, cnidarians and ctenophores have traditionally been labelled diploblastic, along with sponges.[9][10] However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer.[11] As a result, some recent text books classify ctenophores as triploblastic,[12] and it has been suggested that cnidarians evolved from triploblastic ancestors.[11]

text:
Sponges[13][14]
Cnidarians[9][10]
Ctenophores[9][12]
Bilateria[9]

Cnidocytes

No
Yes
No

Colloblasts

No
Yes
No

Digestive and circulatory organs

No
Yes

Number of main cell layers

Two, with jelly-like layer between them
Two[9] or Three[11][12]
Three

Cells in each layer bound together

cell-adhesion molecules, but no basement membranes except Homoscleromorpha.[15]
inter-cell connections; basement membranes

Sensory organs

No
Yes

Number of cells in middle "jelly" layer

Many
Few
(Not applicable)

Cells in outer layers can move inwards and change functions

Yes
No
(Not applicable)

Nervous system

No
Yes, simple
Simple to complex

Muscles

None
Mostly epitheliomuscular
Mostly myoepithelial
Mostly myocytes

tag: table

text: Description[edit]

text: Basic body forms[edit]

text: Most adult cnidarians appear as either swimming medusae or sessile polyps, and many hydrozoan species are known to alternate between the two forms. Both are radially symmetrical, like a wheel and a tube respectively. Since these animals have no heads, their ends are described as "oral" (nearest the mouth) and "aboral" (furthest from the mouth). Most have fringes of tentacles equipped with cnidocytes around their edges, and medusae generally have an inner ring of tentacles around the mouth. Some hydroids may consist of colonies of zooids that serve different purposes, such as defense, reproduction and catching prey. The mesoglea of polyps is usually thin and often soft, but that of medusae is usually thick and springy, so that it returns to its original shape after muscles around the edge have contracted to squeeze water out, enabling medusae to swim by a sort of jet propulsion.[10]

text: Skeletons[edit]

text: In medusae the only supporting structure is the mesoglea. Hydra and most sea anemones close their mouths when they are not feeding, and the water in the digestive cavity then acts as a hydrostatic skeleton, rather like a water-filled balloon. Other polyps such as Tubularia use columns of water-filled cells for support. Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, rather like sponges.[10]

text: In some colonial polyps, a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps. Stony corals secrete massive calcium carbonate exoskeletons. A few polyps collect materials such as sand grains and shell fragments, which they attach to their outsides. Some colonial sea anemones stiffen the mesoglea with sediment particles.[10]

text: Main cell layers[edit]

text: Cnidaria are diploblastic animals; in other words, they have two main cell layers, while more complex animals are triploblasts having three main layers. The two main cell layers of cnidarians form epithelia that are mostly one cell thick, and are attached to a fibrous basement membrane, which they secrete. They also secrete the jelly-like mesoglea that separates the layers. The layer that faces outwards, known as the ectoderm ("outside skin"), generally contains the following types of cells:[9]

text:
Epitheliomuscular cells whose bodies form part of the epithelium but whose bases extend to form muscle fibers in parallel rows.[16] The fibers of the outward-facing cell layer generally run at right angles to the fibers of the inward-facing one. In Anthozoa (anemones, corals, etc.) and Scyphozoa (jellyfish), the mesoglea also contains some muscle cells.[10]
Cnidocytes, the harpoon-like "nettle cells" that give the phylum Cnidaria its name. These appear between or sometimes on top of the muscle cells.[9]
Nerve cells. Sensory cells appear between or sometimes on top of the muscle cells,[9] and communicate via synapses (gaps across which chemical signals flow) with motor nerve cells, which lie mostly between the bases of the muscle cells.[10]
Interstitial cells, which are unspecialized and can replace lost or damaged cells by transforming into the appropriate types. These are found between the bases of muscle cells.[9]

tag: ul

text: In addition to epitheliomuscular, nerve and interstitial cells, the inward-facing gastroderm ("stomach skin") contains gland cells that secrete digestive enzymes. In some species it also contains low concentrations of cnidocytes, which are used to subdue prey that is still struggling.[9][10]

text: The mesoglea contains small numbers of amoeba-like cells,[10] and muscle cells in some species.[9] However, the number of middle-layer cells and types are much lower than in sponges.[10]

text: Polymorphism[edit]

text:
Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa.[17] In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks.[18]
For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.

text: Cnidocytes[edit]

text: These "nettle cells" function as harpoons, since their payloads remain connected to the bodies of the cells by threads. Three types of cnidocytes are known:[9][10]

text:
Nematocysts inject venom into prey, and usually have barbs to keep them embedded in the victims. Most species have nematocysts.[9]
Spirocysts do not penetrate the victim or inject venom, but entangle it by means of small sticky hairs on the thread.
Ptychocysts are not used for prey capture — instead the threads of discharged ptychocysts are used for building protective tubes in which their owners live. Ptychocysts are found only in the order Ceriantharia, tube anemones.[10]

text: The main components of a cnidocyte are:[9][10]

text:
A cilium (fine hair) which projects above the surface and acts as a trigger. Spirocysts do not have cilia.
A tough capsule, the cnida, which houses the thread, its payload and a mixture of chemicals that may include venom or adhesives or both. ("cnida" is derived from the Greek word κνίδη, which means "nettle"[19])
A tube-like extension of the wall of the cnida that points into the cnida, like the finger of a rubber glove pushed inwards. When a cnidocyte fires, the finger pops out. If the cell is a venomous nematocyte, the "finger"'s tip reveals a set of barbs that anchor it in the prey.
The thread, which is an extension of the "finger" and coils round it until the cnidocyte fires. The thread is usually hollow and delivers chemicals from the cnida to the target.
An operculum (lid) over the end of the cnida. The lid may be a single hinged flap or three flaps arranged like slices of pie.
The cell body, which produces all the other parts.

text: It is difficult to study the firing mechanisms of cnidocytes as these structures are small but very complex. At least four hypotheses have been proposed:[9]

text:
Rapid contraction of fibers round the cnida may increase its internal pressure.
The thread may be like a coiled spring that extends rapidly when released.
In the case of Chironex (the "sea wasp"), chemical changes in the cnida's contents may cause them to expand rapidly by polymerization.
Chemical changes in the liquid in the cnida make it a much more concentrated solution, so that osmotic pressure forces water in very rapidly to dilute it. This mechanism has been observed in nematocysts of the class Hydrozoa, sometimes producing pressures as high as 140 atmospheres, similar to that of scuba air tanks, and fully extending the thread in as little as 2 milliseconds (0.002 second).[10]

text: Cnidocytes can only fire once, and about 25% of a hydra's nematocysts are lost from its tentacles when capturing a brine shrimp. Used cnidocytes have to be replaced, which takes about 48 hours. To minimise wasteful firing, two types of stimulus are generally required to trigger cnidocytes: nearby sensory cells detect chemicals in the water, and their cilia respond to contact. This combination prevents them from firing at distant or non-living objects. Groups of cnidocytes are usually connected by nerves and, if one fires, the rest of the group requires a weaker minimum stimulus than the cells that fire first.[9][10]

text: Locomotion[edit]

text: Medusae swim by a form of jet propulsion: muscles, especially inside the rim of the bell, squeeze water out of the cavity inside the bell, and the springiness of the mesoglea powers the recovery stroke. Since the tissue layers are very thin, they provide too little power to swim against currents and just enough to control movement within currents.[10]

text: Hydras and some sea anemones can move slowly over rocks and sea or stream beds by various means: creeping like snails, crawling like inchworms, or by somersaulting. A few can swim clumsily by waggling their bases.[10]

text: Nervous system and senses[edit]

text: Cnidarians are generally thought to have no brains or even central nervous systems. However, they do have integrative areas of neural tissue that could be considered some form of centralization. Most of their bodies are innervated by decentralized nerve nets that control their swimming musculature and connect with sensory structures, though each clade has slightly different structures.[20] These sensory structures, usually called rhopalia, can generate signals in response to various types of stimuli such as light, pressure, and much more. Medusa usually have several of them around the margin of the bell that work together to control the motor nerve net, that directly innervates the swimming muscles. Most Cnidarians also have a parallel system. In scyphozoans, this takes the form of a diffuse nerve net, which has modulatory effects on the nervous system.[21] As well as forming the "signal cables" between sensory neurons and motoneurons, intermediate neurons in the nerve net can also form ganglia that act as local coordination centers. Communication between nerve cells can occur by chemical synapses or gap junctions in hydrozoans, though gap junctions are not present in all groups. Cnidarians have many of the same neurotransmitters as many animals, including chemicals such as glutamate, GABA, and acetylcholine.[22]

text: This structure ensures that the musculature is excited rapidly and simultaneously, and can be directly stimulated from any point on the body, and it also is better able to recover after injury.[20][21]

text: Medusae and complex swimming colonies such as siphonophores and chondrophores sense tilt and acceleration by means of statocysts, chambers lined with hairs which detect the movements of internal mineral grains called statoliths. If the body tilts in the wrong direction, the animal rights itself by increasing the strength of the swimming movements on the side that is too low. Most species have ocelli ("simple eyes"), which can detect sources of light. However, the agile box jellyfish are unique among Medusae because they possess four kinds of true eyes that have retinas, corneas and lenses.[23] Although the eyes probably do not form images, Cubozoa can clearly distinguish the direction from which light is coming as well as negotiate around solid-colored objects.[9][23]

text: Feeding and excretion[edit]

text: Cnidarians feed in several ways: predation, absorbing dissolved organic chemicals, filtering food particles out of the water, obtaining nutrients from symbiotic algae within their cells, and parasitism. Most obtain the majority of their food from predation but some, including the corals Hetroxenia and Leptogorgia, depend almost completely on their endosymbionts and on absorbing dissolved nutrients.[9] Cnidaria give their symbiotic algae carbon dioxide, some nutrients, a place in the sun and protection against predators.[10]

text: Predatory species use their cnidocytes to poison or entangle prey, and those with venomous nematocysts may start digestion by injecting digestive enzymes. The "smell" of fluids from wounded prey makes the tentacles fold inwards and wipe the prey off into the mouth. In medusae the tentacles round the edge of the bell are often short and most of the prey capture is done by "oral arms", which are extensions of the edge of the mouth and are often frilled and sometimes branched to increase their surface area. Medusae often trap prey or suspended food particles by swimming upwards, spreading their tentacles and oral arms and then sinking. In species for which suspended food particles are important, the tentacles and oral arms often have rows of cilia whose beating creates currents that flow towards the mouth, and some produce nets of mucus to trap particles.[9] Their digestion is both intra and extracellular.

text: Once the food is in the digestive cavity, gland cells in the gastroderm release enzymes that reduce the prey to slurry, usually within a few hours. This circulates through the digestive cavity and, in colonial cnidarians, through the connecting tunnels, so that gastroderm cells can absorb the nutrients. Absorption may take a few hours, and digestion within the cells may take a few days. The circulation of nutrients is driven by water currents produced by cilia in the gastroderm or by muscular movements or both, so that nutrients reach all parts of the digestive cavity.[10] Nutrients reach the outer cell layer by diffusion or, for animals or zooids such as medusae which have thick mesogleas, are transported by mobile cells in the mesoglea.[9]

text: Indigestible remains of prey are expelled through the mouth. The main waste product of cells' internal processes is ammonia, which is removed by the external and internal water currents.[10]

text: Respiration[edit]

text: There are no respiratory organs, and both cell layers absorb oxygen from and expel carbon dioxide into the surrounding water. When the water in the digestive cavity becomes stale it must be replaced, and nutrients that have not been absorbed will be expelled with it. Some Anthozoa have ciliated grooves on their tentacles, allowing them to pump water out of and into the digestive cavity without opening the mouth. This improves respiration after feeding and allows these animals, which use the cavity as a hydrostatic skeleton, to control the water pressure in the cavity without expelling undigested food.[9]

text: Cnidaria that carry photosynthetic symbionts may have the opposite problem, an excess of oxygen, which may prove toxic. The animals produce large quantities of antioxidants to neutralize the excess oxygen.[9]

text: Regeneration[edit]

text: All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Medusae have limited ability to regenerate, but polyps can do so from small pieces or even collections of separated cells. This enables corals to recover even after apparently being destroyed by predators.[9]

text: Reproduction[edit]

text: Sexual[edit]

text: Cnidarian sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example, in Scyphozoa (jellyfish) and Cubozoa (box jellies) a larva swims until it finds a good site, and then becomes a polyp. This grows normally but then absorbs its tentacles and splits horizontally into a series of disks that become juvenile medusae, a process called strobilation. The juveniles swim off and slowly grow to maturity, while the polyp re-grows and may continue strobilating periodically. The adults have gonads in the gastroderm, and these release ova and sperm into the water in the breeding season.[9][10]

text: This phenomenon of succession of differently organized generations (one asexually reproducing, sessile polyp, followed by a free-swimming medusa or a sessile polyp that reproduces sexually)[24] is sometimes called "alternation of asexual and sexual phases" or "metagenesis", but should not be confused with the alternation of generations as found in plants.

text: Shortened forms of this life cycle are common, for example some oceanic scyphozoans omit the polyp stage completely, and cubozoan polyps produce only one medusa. Hydrozoa have a variety of life cycles. Some have no polyp stages and some (e.g. hydra) have no medusae. In some species, the medusae remain attached to the polyp and are responsible for sexual reproduction; in extreme cases these reproductive zooids may not look much like medusae. Meanwhile, life cycle reversal, in which polyps are formed directly from medusae without the involvement of sexual reproduction process, was observed in both Hydrozoa (Turritopsis dohrnii[25] and Laodicea undulata[26]) and Scyphozoa (Aurelia sp.1[27]). Anthozoa have no medusa stage at all and the polyps are responsible for sexual reproduction.[9]

text: Spawning is generally driven by environmental factors such as changes in the water temperature, and their release is triggered by lighting conditions such as sunrise, sunset or the phase of the moon. Many species of Cnidaria may spawn simultaneously in the same location, so that there are too many ova and sperm for predators to eat more than a tiny percentage — one famous example is the Great Barrier Reef, where at least 110 corals and a few non-cnidarian invertebrates produce enough gametes to turn the water cloudy. These mass spawnings may produce hybrids, some of which can settle and form polyps, but it is not known how long these can survive. In some species the ova release chemicals that attract sperm of the same species.[9]

text: The fertilized eggs develop into larvae by dividing until there are enough cells to form a hollow sphere (blastula) and then a depression forms at one end (gastrulation) and eventually becomes the digestive cavity. However, in cnidarians the depression forms at the end further from the yolk (at the animal pole), while in bilaterians it forms at the other end (vegetal pole).[10] The larvae, called planulae, swim or crawl by means of cilia.[9] They are cigar-shaped but slightly broader at the "front" end, which is the aboral, vegetal-pole end and eventually attaches to a substrate if the species has a polyp stage.[10]

text: Anthozoan larvae either have large yolks or are capable of feeding on plankton, and some already have endosymbiotic algae that help to feed them. Since the parents are immobile, these feeding capabilities extend the larvae's range and avoid overcrowding of sites. Scyphozoan and hydrozoan larvae have little yolk and most lack endosymbiotic algae, and therefore have to settle quickly and metamorphose into polyps. Instead, these species rely on their medusae to extend their ranges.[10]

text: Asexual[edit]

text: All known cnidaria can reproduce asexually by various means, in addition to regenerating after being fragmented. Hydrozoan polyps only bud, while the medusae of some hydrozoans can divide down the middle. Scyphozoan polyps can both bud and split down the middle. In addition to both of these methods, Anthozoa can split horizontally just above the base. Asexual reproduction makes the daughter cnidarian a clone of the adult.[9][10]

text: Classification[edit]

text: Cnidarians were for a long time grouped with Ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Modern cnidarians are generally classified into four main classes:[9] sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa (jellyfish) and 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 are now recognized as highly derived cnidarians rather than more closely related to the bilaterians.[6][28]

text:
Hydrozoa
Scyphozoa
Cubozoa
Anthozoa

Number of species[5]

3,600
228
42
6,100

Examples

Hydra, siphonophores
Jellyfish
Box jellies
Sea anemones, corals, sea pens

Cells found in mesoglea

No
Yes
Yes
Yes

Nematocysts in exodermis

No
Yes
Yes
Yes

Medusa phase in life cycle

In some species
Yes
Yes
No

Number of medusae produced per polyp

Many
Many
One
(not applicable)

text: Stauromedusae, small sessile cnidarians with stalks and no medusa stage, have traditionally been classified as members of the Scyphozoa, but recent research suggests they should be regarded as a separate class, Staurozoa.[29]

text:
The Myxozoa, microscopic parasites, were first classified as protozoans.[30]  Research then suggested that Polypodium hydriforme, a parasite within the egg cells of sturgeon, is closely related to the Myxozoa and that both Polypodium and the Myxozoa were intermediate between cnidarians and bilaterian animals.[31] More recent research demonstrated that the previous identification of bilaterian genes
reflected contamination of the Myxozoan samples by material from their host organism, and they are now firmly identified as heavily derived cnidarians, and more closely related to Hydrozoa and Scyphozoa than to Anthozoa.[32][6][28][33]

text: Some researchers classify the extinct conulariids as cnidarians, while others propose that they form a completely separate phylum.[34]

text: Current classification according to the World Register of Marine Species :

text:
class Anthozoa Ehrenberg, 1834
subclass Ceriantharia Perrier, 1893 — Tube-dwelling anemones
subclass Hexacorallia Haeckel, 1896 - stony corals
subclass Octocorallia Haeckel, 1866 - soft corals and sea fans
class Cubozoa Werner, 1973 -- box jellies
class Hydrozoa Owen, 1843 -- hydrozoans (fire corals, hydroids, hydroid jellyfishes, siphonophores...)
class Myxozoa -- minute polyps
class Polypodiozoa Raikova, 1994 (uncertain status)
class Scyphozoa Goette, 1887 -- "true" jellyfishes
class Staurozoa Marques & Collins, 2004 -- stalked jellyfishes

text:
Cerianthus filiformis (Ceriantharia)

Sea anemones (Actinaria, part of Hexacorallia)

Coral Acropora muricata (Scleractinia, part of Hexacorallia)

Sea fan Gorgonia ventalina (Alcyonacea, part of Octocorallia)

Bok jellyfishCarybdea branchi (Cubozoa)

Siphonophore Physalia physalis (Hydrozoa)

Myxobolus cerebralis (Myxozoa)

Polypodium hydriforme (Polypodiozoa)

Jellyfish Phyllorhiza punctata (Scyphozoa)

Stalked jelly Haliclystus antarcticus (Staurozoa)

text: Ecology[edit]

text:
Many cnidarians are limited to shallow waters because they depend on endosymbiotic algae for much of their nutrients. The life cycles of most have polyp stages, which are limited to locations that offer stable substrates. Nevertheless, major cnidarian groups contain species that have escaped these limitations. Hydrozoans have a worldwide range: some, such as Hydra, live in freshwater; Obelia appears in the coastal waters of all the oceans; and Liriope can form large shoals near the surface in mid-ocean. Among anthozoans, a few scleractinian corals, sea pens and sea fans live in deep, cold waters, and some sea anemones inhabit polar seabeds while others live near hydrothermal vents over 10 km (6.2 mi) below sea-level. Reef-building corals are limited to tropical seas between 30°N and 30°S with a maximum depth of 46 m (151 ft), temperatures between 20 °C (68 °F) and 28 °C (82 °F) high salinity and low carbon dioxide levels. Stauromedusae, although usually classified as jellyfish, are stalked, sessile animals that live in cool to Arctic waters.[35]
Cnidarians range in size from a mere handful of cells for myxozoan[28]
through Hydra's 5–20 mm (0.20–0.79 in) long,[36] to the Lion's mane jellyfish, which may exceed 2 m (6.6 ft) in diameter and 75 m (246 ft) in length.[37]

text: Prey of cnidarians ranges from plankton to animals several times larger than themselves.[35][38] Some cnidarians are parasites, mainly on jellyfish but a few are major pests of fish.[35] Others obtain most of their nourishment from endosymbiotic algae or dissolved nutrients.[9] Predators of cnidarians include: sea slugs, which can incorporate nematocysts into their own bodies for self-defense;[39] starfish, notably the crown of thorns starfish, which can devastate corals;[35] butterfly fish and parrot fish, which eat corals;[40] and marine turtles, which eat jellyfish.[37] Some sea anemones and jellyfish have a symbiotic relationship with some fish; for example clown fish live among the tentacles of sea anemones, and each partner protects the other against predators.[35]

text: Coral reefs form some of the world's most productive ecosystems. Common coral reef cnidarians include both Anthozoans (hard corals, octocorals, anemones) and Hydrozoans (fire corals, lace corals). The endosymbiotic algae of many cnidarian species are very effective primary producers, in other words converters of inorganic chemicals into organic ones that other organisms can use, and their coral hosts use these organic chemicals very efficiently. In addition, reefs provide complex and varied habitats that support a wide range of other organisms.[41] Fringing reefs just below low-tide level also have a mutually beneficial relationship with mangrove forests at high-tide level and seagrass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and seagrass protect the coral from large influxes of silt, fresh water and pollutants. This additional level of variety in the environment is beneficial to many types of coral reef animals, which for example may feed in the sea grass and use the reefs for protection or breeding.[42]

text: Evolutionary history[edit]

text: Fossil record[edit]

text: The earliest widely accepted animal fossils are rather modern-looking cnidarians, possibly from around 580 million years ago, although fossils from the Doushantuo Formation can only be dated approximately.[43] The identification of some of these as embryos of animals has been contested, but other fossils from these rocks strongly resemble tubes and other mineralized structures made by corals.[44] Their presence implies that the cnidarian and bilaterian lineages had already diverged.[45] Although the Ediacaran fossil Charnia used to be classified as a jellyfish or sea pen,[46] more recent study of growth patterns in Charnia and modern cnidarians has cast doubt on this hypothesis,[47][48] leaving only the Canadian polyp, Haootia, as the only bona-fide cnidarian body fossil from the Ediacaran. Few fossils of cnidarians without mineralized skeletons are known from more recent rocks, except in lagerstätten that preserved soft-bodied animals.[49]

text: A few mineralized fossils that resemble corals have been found in rocks from the Cambrian period, and corals diversified in the Early Ordovician.[49] These corals, which were wiped out in the Permian-Triassic extinction about 251 million years ago,[49] did not dominate reef construction since sponges and algae also played a major part.[50] During the Mesozoic era rudist bivalves were the main reef-builders, but they were wiped out in the Cretaceous–Paleogene extinction event 66 million years ago,[51] and since then the main reef-builders have been scleractinian corals.[49]

text: Family tree[edit]

text:
Metazoa

Glass sponges

Demosponges

Calcareous sponges

Eumetazoa

Ctenophora (comb jellies)

Planulozoa

Cnidaria

Anthozoa(sea anemones and corals)

Myxozoa

Medusozoa

Hydrozoa(Hydra, siphonophores, etc.)

Cubozoa(box jellies)

Staurozoa

"Scyphozoa"(jellyfish, excludingStaurozoa)

Placozoa

Bilateria

text: It is difficult to reconstruct the early stages in the evolutionary "family tree" of animals using only morphology (their shapes and structures), because the large differences between Porifera (sponges), Cnidaria plus Ctenophora (comb jellies), Placozoa and Bilateria (all the more complex animals) make comparisons difficult. Hence reconstructions now rely largely or entirely on molecular phylogenetics, which groups organisms according to similarities and differences in their biochemistry, usually in their DNA or RNA.[55]

text: It is now generally thought that the Calcarea (sponges with calcium carbonate spicules) are more closely related to Cnidaria, Ctenophora (comb jellies) and Bilateria (all the more complex animals) than they are to the other groups of sponges.[52][56][57] In 1866 it was proposed that Cnidaria and Ctenophora were more closely related to each other than to Bilateria and formed a group called Coelenterata ("hollow guts"), because Cnidaria and Ctenophora both rely on the flow of water in and out of a single cavity for feeding, excretion and respiration. In 1881, it was proposed that Ctenophora and Bilateria were more closely related to each other, since they shared features that Cnidaria lack, for example muscles in the middle layer (mesoglea in Ctenophora, mesoderm in Bilateria). However more recent analyses indicate that these similarities are rather vague, and the current view, based on molecular phylogenetics, is that Cnidaria and Bilateria are more closely related to each other than either is to Ctenophora. This grouping of Cnidaria and Bilateria has been labelled "Planulozoa" because it suggests that the earliest Bilateria were similar to the planula larvae of Cnidaria.[2][53]

text: Within the Cnidaria, the Anthozoa (sea anemones and corals) are regarded as the sister-group of the rest, which suggests that the earliest cnidarians were sessile polyps with no medusa stage. However, it is unclear how the other groups acquired the medusa stage, since Hydrozoa form medusae by budding from the side of the polyp while the other Medusozoa do so by splitting them off from the tip of the polyp. The traditional grouping of Scyphozoa included the Staurozoa, but morphology and molecular phylogenetics indicate that Staurozoa are more closely related to Cubozoa (box jellies) than to other "Scyphozoa". Similarities in the double body walls of Staurozoa and the extinct Conulariida suggest that they are closely related. The position of Anthozoa nearest the beginning of the cnidarian family tree also implies that Anthozoa are the cnidarians most closely related to Bilateria, and this is supported by the fact that Anthozoa and Bilateria share some genes that determine the main axes of the body.[2][58]

text: However, in 2005 Katja Seipel and Volker Schmid suggested that cnidarians and ctenophores are simplified descendants of triploblastic animals, since ctenophores and the medusa stage of some cnidarians have striated muscle, which in bilaterians arises from the mesoderm. They did not commit themselves on whether bilaterians evolved from early cnidarians or from the hypothesized triploblastic ancestors of cnidarians.[11]

text: In molecular phylogenetics analyses from 2005 onwards, important groups of developmental genes show the same variety in cnidarians as in chordates.[59] In fact cnidarians, and especially anthozoans (sea anemones and corals), retain some genes that are present in bacteria, protists, plants and fungi but not in bilaterians.[60]

text: The mitochondrial genome in the medusozoan cnidarians, unlike those in other animals, is linear with fragmented genes.[61] The reason for this difference is unknown.

text: Interaction with humans[edit]

text: Jellyfish stings killed about 1,500 people in the 20th century,[62] and cubozoans are particularly dangerous. On the other hand, some large jellyfish are considered a delicacy in East and Southeast Asia. Coral reefs have long been economically important as providers of fishing grounds, protectors of shore buildings against currents and tides, and more recently as centers of tourism. However, they are vulnerable to over-fishing, mining for construction materials, pollution, and damage caused by tourism.

text: Beaches protected from tides and storms by coral reefs are often the best places for housing in tropical countries. Reefs are an important food source for low-technology fishing, both on the reefs themselves and in the adjacent seas.[63] However, despite their great productivity, reefs are vulnerable to over-fishing, because much of the organic carbon they produce is exhaled as carbon dioxide by organisms at the middle levels of the food chain and never reaches the larger species that are of interest to fishermen.[41] Tourism centered on reefs provides much of the income of some tropical islands, attracting photographers, divers and sports fishermen. However, human activities damage reefs in several ways: mining for construction materials; pollution, including large influxes of fresh water from storm drains; commercial fishing, including the use of dynamite to stun fish and the capture of young fish for aquariums; and tourist damage caused by boat anchors and the cumulative effect of walking on the reefs.[63] Coral, mainly from the Pacific Ocean has long been used in jewellery, and demand rose sharply in the 1980s.[64]

text: Some large jellyfish species of the Rhizostomae order are commonly consumed in Japan, Korea and Southeast Asia.[65][66][67] In parts of the range, fishing industry is restricted to daylight hours and calm conditions in two short seasons, from March to May and August to November.[67] The commercial value of jellyfish food products depends on the skill with which they are prepared, and "Jellyfish Masters" guard their trade secrets carefully. Jellyfish is very low in cholesterol and sugars, but cheap preparation can introduce undesirable amounts of heavy metals.[68]

text: The "sea wasp" Chironex fleckeri has been described as the world's most venomous jellyfish and is held responsible for 67 deaths, although it is difficult to identify the animal as it is almost transparent. Most stingings by C. fleckeri cause only mild symptoms.[69] Seven other box jellies can cause a set of symptoms called Irukandji syndrome,[70] which takes about 30 minutes to develop,[71] and from a few hours to two weeks to disappear.[72] Hospital treatment is usually required, and there have been a few deaths.[70]

text: A number of Myxozoans are commercially important pathogens in salmonid aquaculture.

text: Notes[edit]

text:
Jump up ^ Classes in Medusozoa based on "ITIS Report – Taxon: Subphylum Medusozoa". Universal Taxonomic Services. Retrieved 2018-03-18.

^ Jump up to: a b c d Collins, A.G. (May 2002). "Phylogeny of Medusozoa and the Evolution of Cnidarian Life Cycles" (PDF). Journal of Evolutionary Biology. 15 (3): 418–432. doi:10.1046/j.1420-9101.2002.00403.x. Retrieved 2008-11-27.

Jump up ^ Subphyla Anthozoa and Medusozoa based on "The Taxonomicon – Taxon: Phylum Cnidaria". Universal Taxonomic Services. Archived from the original on 2007-09-29. Retrieved 2007-07-10.

Jump up ^ Dictionary.com Unabridged. Random House, Inc. Cnidaria. Retrieved May 15, 2013.

^ Jump up to: a b Zhang, Z.-Q. (2011). "Animal biodiversity: An introduction to higher-level classification and taxonomic richness" (PDF). Zootaxa. 3148: 7–12.

^ Jump up to: a b c d E. Jímenez-Guri;  et al. (July 2007). "Buddenbrockia is a cnidarian worm". Science. 317 (116): 116–118. Bibcode:2007Sci...317..116J. doi:10.1126/science.1142024. PMID 17615357.

Jump up ^ Zapata F, Goetz FE, Smith SA, Howison M, Siebert S, Church SH,  et al. (2015). "Phylogenomic Analyses Support Traditional Relationships within Cnidaria". PLOS ONE. 10 (10): e0139068. Bibcode:2015PLoSO..1039068Z. doi:10.1371/journal.pone.0139068. PMC 4605497. PMID 26465609.

Jump up ^ Park E, Hwang D, Lee J, Song J, Seo T, Won Y (January 2012). "Estimation of divergence times in cnidarian evolution based on mitochondrial protein-coding genes and the fossil record". Molecular Phylogenetics & Evolution. 62 (1): 329–45. doi:10.1016/j.ympev.2011.10.008. PMID 22040765.

^ Jump up to: a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af Hinde, R.T. (1998). "The Cnidaria and Ctenophora".  In Anderson, D.T. Invertebrate Zoology. Oxford University Press. pp. 28–57. ISBN 0-19-551368-1.

^ Jump up to: a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac Ruppert, E.E.; Fox, R.S. & Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 111–124. ISBN 0-03-025982-7.

^ Jump up to: a b c d Seipel, K.; Schmid, V. (June 2005). "Evolution of striated muscle: Jellyfish and the origin of triploblasty". Developmental Biology. 282 (1): 14–26. doi:10.1016/j.ydbio.2005.03.032. PMID 15936326.

^ Jump up to: a b c Ruppert, E.E.; Fox, R.S. & Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 182–195. ISBN 0-03-025982-7.

Jump up ^ Ruppert, E.E.; Fox, R.S. & Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 76–97. ISBN 0-03-025982-7.

Jump up ^ Bergquist, P.R. (1998). "Porifera".  In Anderson, D.T. Invertebrate Zoology. Oxford University Press. pp. 10–27. ISBN 0-19-551368-1.

Jump up ^ Exposito, J-Y.; Cluzel, C.; Garrone, R. & Lethias, C. (2002). "Evolution of collagens". The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology. 268 (3): 302–316. doi:10.1002/ar.10162. PMID 12382326.

Jump up ^ Ruppert, E.E.; Fox, R.S. & Barnes, R.D. (2004). "Introduction to Metazoa". Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 103–104. ISBN 0-03-025982-7.

Jump up ^ Ford, E.B. (1965). Genetic polymorphism. London: Faber & Faber. ISBN 0262060124.

Jump up ^ Dunn, Casey W.; Wagner, Günter P. (16 September 2006). "The evolution of colony-level development in the Siphonophora (Cnidaria:Hydrozoa)". Development Genes and Evolution. 216 (12): 743–754. doi:10.1007/s00427-006-0101-8. PMID 16983540.

Jump up ^ Trumble, W.; Brown, L. (2002). "Cnida". Shorter Oxford English Dictionary. Oxford University Press.

^ Jump up to: a b Satterlie, Richard A. (15 April 2011). "Do jellyfish have central nervous systems?". Journal of Experimental Biology. 214 (8): 1215–1223. doi:10.1242/jeb.043687. ISSN 0022-0949. PMID 21430196.

^ Jump up to: a b Satterlie, Richard A (2002-10-01). "Neuronal control of swimming in jellyfish: a comparative story". Canadian Journal of Zoology. 80 (10): 1654–1669. doi:10.1139/z02-132. ISSN 0008-4301.

Jump up ^ Kass-Simon, G.; Pierobon, Paola (1 January 2007). "Cnidarian chemical neurotransmission, an updated overview". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 146 (1): 9–25. doi:10.1016/j.cbpa.2006.09.008. PMID 17101286.

^ Jump up to: a b "Jellyfish Have Human-Like Eyes". www.livescience.com. April 1, 2007. Retrieved 2012-06-12.

Jump up ^ Vernon A. Harris (1990). "Hydroids". Sessile animals of the sea shore. Springer. p. 223, [1].

Jump up ^ Bavestrello;  et al. (1992). "Bi-directional conversion in Turritopsis nutricula (Hydrozoa)" (PDF). Scientia Marina. Retrieved 2015-12-31.

Jump up ^ De Vito;  et al. (2006). "Evidence of reverse development in Leptomedusae (Cnidaria, Hydrozoa): the case of Laodicea undulata (Forbes and Goodsir 1851)". Marine Biology. 149: 339–346. doi:10.1007/s00227-005-0182-3. Retrieved 2015-12-31.

Jump up ^ He;  et al. (21 December 2015). "Life Cycle Reversal in Aurelia sp.1 (Cnidaria, Scyphozoa)". PLOS ONE. 10: e0145314. Bibcode:2015PLoSO..1045314H. doi:10.1371/journal.pone.0145314. PMC 4687044. PMID 26690755. Retrieved 2015-12-31.

^ Jump up to: a b c Schuster, Ruth (20 November 2015). "Microscopic parasitic jellyfish defy everything we know, astonish scientists". Haaretz. Retrieved 4 April 2018.

Jump up ^ Collins, A.G.; Cartwright, P.; McFadden, C.S. & Schierwater, B. (2005). "Phylogenetic Context and Basal Metazoan Model Systems". Integrative and Comparative Biology. 45 (4): 585–594. doi:10.1093/icb/45.4.585. PMID 21676805.

Jump up ^
Štolc, A. (1899). "Actinomyxidies, nouveau groupe de Mesozoaires parent des Myxosporidies". Bull. Int. L'Acad. Sci. Bohème. 12: 1–12.

Jump up ^ Zrzavý, J.; Hypša, V. (April 2003). "Myxozoa, Polypodium, and the origin of the Bilateria: The phylogenetic position of "Endocnidozoa" in light of the rediscovery of Buddenbrockia". Cladistics. 19 (2): 164–169. doi:10.1111/j.1096-0031.2003.tb00305.x.

Jump up ^
E. Jímenez-Guri; Philippe, H; Okamura, B; Holland, PW (July 2007). "Buddenbrockia is a cnidarian worm". Science. 317 (116): 116–118. Bibcode:2007Sci...317..116J. doi:10.1126/science.1142024. PMID 17615357.

Jump up ^ Chang, E. Sally; Neuhof, Moran; Rubinstein, Nimrod D.; Diamant, Arik; Philippe, Hervé; Huchon, Dorothée; Cartwright, Paulyn (1 December 2015). "Genomic insights into the evolutionary origin of Myxozoa within Cnidaria". Proceedings of the National Academy of Sciences. 112 (48): 14912–14917. Bibcode:2015PNAS..11214912C. doi:10.1073/pnas.1511468112. PMC 4672818. PMID 26627241.

Jump up ^ "The Conulariida". University of California Museum of Paleontology. Retrieved 2008-11-27.

^ Jump up to: a b c d e Shostak, S. (2006). "Cnidaria (Coelenterates)". Encyclopedia of Life Sciences. John Wiley & Sons. doi:10.1038/npg.els.0004117.

Jump up ^ Blaise, C.; Férard, J-F. (2005). Small-scale Freshwater Toxicity Investigations: Toxicity Test Methods. Springer. p. 398. ISBN 1-4020-3119-X. Retrieved 2008-11-21.

^ Jump up to: a b Safina, C. (2007). Voyage of the Turtle: In Pursuit of the Earth's Last Dinosaur. Macmillan. p. 154. ISBN 0-8050-8318-9. Retrieved 2008-11-21.

Jump up ^ Cowen, R. (2000). History of Life (3 ed.). Blackwell. p. 54. ISBN 0-632-04444-6. Retrieved 2008-11-21.

Jump up ^ Frick, K (2003). "Predator Suites and Flabellinid Nudibranch Nematocyst Complements in the Gulf of Maine". In: SF Norton (ed). Diving for Science...2003. Proceedings of the American Academy of Underwater Sciences (22nd Annual Scientific Diving Symposium). Retrieved 2008-07-03.

Jump up ^ Choat, J.H.; Bellwood, D.R. (1998).  Paxton, J.R.; Eschmeyer, W.N., eds. Encyclopedia of Fishes. San Diego: Academic Press. pp. 209–211. ISBN 0-12-547665-5.

^ Jump up to: a b Barnes, R.S.K.; Mann, K.H. (1991). Fundamentals of Aquatic Ecology. Blackwell Publishing. pp. 217–227. ISBN 0-632-02983-8. Retrieved 2008-11-26.

Jump up ^ Hatcher, B.G.; Johannes, R.E. & Robertson, A.J. (1989). "Conservation of Shallow-water Marine Ecosystems". Oceanography and Marine Biology: An Annual Review: Volume 27. Routledge. p. 320. ISBN 0-08-037718-1. Retrieved 2008-11-21.

Jump up ^ Chen, J-Y.; Oliveri, P; Li, CW; Zhou, GQ; Gao, F; Hagadorn, JW; Peterson, KJ; Davidson, EH (25 April 2000). "Putative phosphatized embryos from the Doushantuo Formation of China". Proceedings of the National Academy of Sciences. 97 (9): 4457–4462. Bibcode:2000PNAS...97.4457C. doi:10.1073/pnas.97.9.4457. PMC 18256. PMID 10781044. Retrieved 2009-04-30.

Jump up ^ Xiao, S.; Yuan, X. & Knoll, A.H. (5 December 2000). "Eumetazoan fossils in terminal Proterozoic phosphorites?". Proceedings of the National Academy of Sciences. 97 (25): 13684–13689. Bibcode:2000PNAS...9713684X. doi:10.1073/pnas.250491697. PMC 17636. PMID 11095754.

Jump up ^ Chen, J.-Y.; Oliveri, P.; Gao, F.; Dornbos, S.Q.; Li, C-W.; Bottjer, D.J. & Davidson, E.H. (August 2002). "Precambrian Animal Life: Probable Developmental and Adult Cnidarian Forms from Southwest China" (PDF). Developmental Biology. 248 (1): 182–196. doi:10.1006/dbio.2002.0714. PMID 12142030. Retrieved 2008-09-03.

Jump up ^ Donovan, Stephen K.; Lewis, David N. (2001). "Fossils explained 35. The Ediacaran biota". Geology Today (abstract). 17 (3): 115–120. doi:10.1046/j.0266-6979.2001.00285.x.

Jump up ^ Antcliffe, J.B.; Brasier, M. D. (2007). "Charnia and sea pens are poles apart". Journal of the Geological Society. 164 (1): 49–51. doi:10.1144/0016-76492006-080.

Jump up ^ Antcliffe, J.B.; Brasier, Martin D. (2007). "Charnia At 50: Developmental Models For Ediacaran Fronds". Palaeontology. 51 (1): 11–26. doi:10.1111/j.1475-4983.2007.00738.x.

^ Jump up to: a b c d "Cnidaria: Fossil Record". University of California Museum of Paleontology. Retrieved 2008-11-27.

Jump up ^ Copper, P. (January 1994). "Ancient reef ecosystem expansion and collapse". Coral Reefs. 13 (1): 3–11. Bibcode:1994CorRe..13....3C. doi:10.1007/BF00426428.

Jump up ^ "The Rudists". University of California Museum of Paleontology. Retrieved 2008-11-27.

^ Jump up to: a b Borchiellini, C.; Manuel, M.; Alivon, E.; Boury-Esnault, N.; Vacelet J. & Le Parco, Y. (January 2001). "Sponge paraphyly and the origin of Metazoa". Journal of Evolutionary Biology. 14 (1): 171–179. doi:10.1046/j.1420-9101.2001.00244.x.

^ Jump up to: a b Wallberg, A.; Thollesson, M.; Farris, J.S. & Jondelius, U. (2004). "The phylogenetic position of the comb jellies (Ctenophora) and the importance of taxonomic sampling". Cladistics. 20 (6): 558–578. doi:10.1111/j.1096-0031.2004.00041.x.

Jump up ^ Philippe, H.; Derelle, Romain; Lopez, Philippe; Pick, Kerstin; Borchiellini, Carole; Boury-Esnault, Nicole; Vacelet, Jean; Renard, Emmanuelle;  et al. (April 2009). "Phylogenomics Revives Traditional Views on Deep Animal Relationships". Current Biology. 19 (8): 706–712. doi:10.1016/j.cub.2009.02.052. PMID 19345102. Retrieved 2011-09-25.

Jump up ^ Halanych, K.M. (December 2004). "The New View of Animal Phylogeny" (PDF). Annual Review of Ecology, Evolution, and Systematics. 35: 229–256. doi:10.1146/annurev.ecolsys.35.112202.130124. Retrieved 2008-11-27.

Jump up ^ Medina, M.; Collins, A.G.; Silberman, J.D. & Sogin, M.L. (August 2001). "Evaluating hypotheses of basal animal phylogeny using complete sequences of large and small subunit rRNA". Proceedings of the National Academy of Sciences. 98 (17): 9707–9712. Bibcode:2001PNAS...98.9707M. doi:10.1073/pnas.171316998. PMC 55517. PMID 11504944.

Jump up ^ Müller, W.E.G.; Li, J.; Schröder, H.C.; Qiao, L. & Wang, X. (2007). "The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review". Biogeosciences. 4 (2): 219–232. doi:10.5194/bg-4-219-2007.

Jump up ^ Marques, A.C.; Collins, A.G. (2004). "Cladistic analysis of Medusozoa and cnidarian evolution". Invertebrate Biology. 123 (1): 23–42. doi:10.1111/j.1744-7410.2004.tb00139.x. Retrieved 2008-11-27.

Jump up ^ Miller, D.J.; Ball, E.E. & Technau, U. (October 2005). "Cnidarians and ancestral genetic complexity in the animal kingdom". Trends in Genetics. 21 (10): 536–539. doi:10.1016/j.tig.2005.08.002. PMID 16098631.

Jump up ^ Technau, U.; Rudd, S. & Maxwell, P (December 2005). "Maintenance of ancestral complexity and non-metazoan genes in two basal cnidarians". Trends in Genetics. 21 (12): 633–639. doi:10.1016/j.tig.2005.09.007. PMID 16226338.

Jump up ^ Smith, D. R.; Kayal, E.; Yanagihara, A. A.; Collins, A. G.; Pirro, S.; Keeling, P. J. (2011). "First Complete Mitochondrial Genome Sequence from a Box Jellyfish Reveals a Highly Fragmented Linear Architecture and Insights into Telomere Evolution". Genome Biology and Evolution. 4: 52–58. doi:10.1093/gbe/evr127.

Jump up ^ Williamson, J.A.; Fenner, P.J.; Burnett, J.W. & Rifkin, J. (1996). Venomous and Poisonous Marine Animals: A Medical and Biological Handbook. UNSW Press. pp. 65–68. ISBN 0-86840-279-6. Retrieved 2008-10-03.

^ Jump up to: a b Clark, J.R. (1998). Coastal Seas: The Conservation Challenge. Blackwell. pp. 8–9. ISBN 0-632-04955-3. Retrieved 2008-11-28.

Jump up ^ Cronan, D.S. (1991). Marine Minerals in Exclusive Economic Zones. Springer. pp. 63–65. ISBN 0-412-29270-X. Retrieved 2008-11-28.

Jump up ^ Kitamura, M.; Omori, M. (2010). "Synopsis of edible jellyfishes collected from Southeast Asia, with notes on jellyfish fisheries". Plankton and Benthos Research. 5 (3): 106–118. doi:10.3800/pbr.5.106. ISSN 1880-8247.

Jump up ^ Omori, M.; Kitamura, M. (2004). "Taxonomic review of three Japanese species of edible jellyfish (Scyphozoa: Rhizostomeae)". Plankton Biol. Ecol. 51 (1): 36–51.

^ Jump up to: a b Omori, M.; Nakano, E. (May 2001). "Jellyfish fisheries in southeast Asia". Hydrobiologia. 451: 19–26. doi:10.1023/A:1011879821323.

Jump up ^ Y-H. Peggy Hsieh; Fui-Ming Leong; Jack Rudloe (May 2001). "Jellyfish as food". Hydrobiologia. 451 (1–3): 11–17. doi:10.1023/A:1011875720415.

Jump up ^ Greenberg, M.I.; Hendrickson, R.G.; Silverberg, M.; Campbell, C. & Morocco, A. (2004). "Box Jellyfish Envenomation". Greenberg's Text-atlas of Emergency Medicine. Lippincott Williams & Wilkins. p. 875. ISBN 0-7817-4586-1.

^ Jump up to: a b Little, M.; Pereira, P.; Carrette, T. & Seymour, J. (June 2006). "Jellyfish Responsible for Irukandji Syndrome". QJM. 99 (6): 425–427. doi:10.1093/qjmed/hcl057. PMID 16687419.

Jump up ^ Barnes, J. (1964). "Cause and effect in Irukandji stingings". Medical Journal of Australia. 1: 897–904. PMID 14172390.

Jump up ^ Grady J, Burnett J (December 2003). "Irukandji-like syndrome in South Florida divers". Annals of Emergency Medicine. 42 (6): 763–6. doi:10.1016/S0196-0644(03)00513-4. PMID 14634600.

tag: ol

text: Further reading[edit]

text: Books[edit]

text:
Arai, M.N. (1997). A Functional Biology of Scyphozoa. London: Chapman & Hall [p. 316]. ISBN 0-412-45110-7.
Ax, P. (1999). Das System der Metazoa I. Ein Lehrbuch der phylogenetischen Systematik. Gustav Fischer, Stuttgart-Jena: Gustav Fischer. ISBN 3-437-30803-3.
Barnes, R.S.K., P. Calow, P. J. W. Olive, D. W. Golding & J. I. Spicer (2001). The invertebrates—a synthesis. Oxford: Blackwell. 3rd edition [chapter 3.4.2, p. 54]. ISBN 0-632-04761-5.
Brusca, R.C., G.J. Brusca (2003). Invertebrates. Sunderland, Mass.: Sinauer Associates. 2nd edition [chapter 8, p. 219]. ISBN 0-87893-097-3.
Dalby, A. (2003). Food in the Ancient World: from A to Z. London: Routledge.
Moore, J.(2001). An Introduction to the Invertebrates. Cambridge: Cambridge University Press [chapter 4, p. 30]. ISBN 0-521-77914-6.
Schäfer, W. (1997). Cnidaria, Nesseltiere. In Rieger, W. (ed.) Spezielle Zoologie. Teil 1. Einzeller und Wirbellose Tiere. Stuttgart-Jena: Gustav Fischer. Spektrum Akademischer Verl., Heidelberg, 2004. ISBN 3-8274-1482-2.
Werner, B. 4. Stamm Cnidaria. In: V. Gruner (ed.) Lehrbuch der speziellen Zoologie. Begr. von Kaestner. 2 Bde. Stuttgart-Jena: Gustav Fischer, Stuttgart-Jena. 1954, 1980, 1984, Spektrum Akad. Verl., Heidelberg-Berlin, 1993. 5th edition. ISBN 3-334-60474-8.

text: Journal articles[edit]

text:
D. Bridge, B. Schierwater, C. W. Cunningham, R. DeSalle R, L. W. Buss: Mitochondrial DNA structure and the molecular phylogeny of recent cnidaria classes. in: Proceedings of the Academy of Natural Sciences of Philadelphia. Philadelphia USA 89.1992, p. 8750. ISSN 0097-3157
D. Bridge, C. W. Cunningham, R. DeSalle, L. W. Buss: Class-level relationships in the phylum Cnidaria—Molecular and morphological evidence. in: Molecular biology and evolution. Oxford University Press, Oxford 12.1995, p. 679. ISSN 0737-4038
D. G. Fautin: Reproduction of Cnidaria. in: Canadian Journal of Zoology. Ottawa Ont. 80.2002, p. 1735. (PDF, online) ISSN 0008-4301
G. O. Mackie: What's new in cnidarian biology? in: Canadian Journal of Zoology. Ottawa Ont. 80.2002, p. 1649. (PDF, online) ISSN 0008-4301
P. Schuchert: Phylogenetic analysis of the Cnidaria. in: Zeitschrift für zoologische Systematik und Evolutionsforschung. Paray, Hamburg-Berlin 31.1993, p. 161. ISSN 0044-3808
G. Kass-Simon, A. A. Scappaticci Jr.: The behavioral and developmental physiology of nematocysts. in: Canadian Journal of Zoology. Ottawa Ont. 80.2002, p. 1772. (PDF, online) ISSN 0044-3808
J. Zrzavý (2001). "The interrelationships of metazoan parasites: a review of phylum- and higher-level hypotheses from recent morphological and molecular phylogenetic analyses" (PDF). Folia Parasitologica. 48 (2): 81–103. doi:10.14411/fp.2001.013. PMID 11437135. Archived from the original (PDF) on 2007-10-25. Retrieved 2009-01-26.


document_title: Bubba Gump Shrimp Company

question_text: when did the first bubba gump shrimp open

text: Bubba Gump Shrimp Company

text: History[edit]

text: In 1995, Paramount Pictures approached Rusty Pelican Restaurants Inc. with a desire to create a restaurant based on a theme from Paramount's 1994 film Forrest Gump. The Bubba Gump Shrimp Co. was created as a result. Within a year the Bubba Gump Shrimp Co. created a concept idea for the restaurant chain which was then licensed by Paramount Licensing, Inc. In 1996, the first Bubba Gump Shrimp Co. restaurant was opened in Monterey, California; its success led to its franchising on an international scale.[2]

text: In November 2010, Landry's, Inc. acquired Bubba Gump Shrimp Co. for an undisclosed amount.[3] The Bubba Gump Shrimp Co. purchase also included a lone Rusty Pelican in Newport Beach, California.

text: Like the name suggests, Bubba Gump Shrimp Co.'s menu consists mostly of shrimp dishes and other seafood, as well as Southern and Cajun cuisine. The restaurant offers dishes named after characters in the movie, like Jenny’s Catch and the restaurant’s bestseller Forrest’s Seafood Feast.[4][5] Restaurants display movie memorabilia throughout the restaurant. Guests can play Forrest Gump movie trivia and can signal their waiter with a “Stop, Forrest, Stop” sign. Bubba Gump Shrimp Co. also has a children’s menu.

text: Locations[edit]

text:
Anaheim - Anaheim GardenWalk
Ara Damansara - Citta Mall
Baltimore - Inner Harbor
Bandar Sunway - Sunway Pyramid
Biloxi - Golden Nugget Biloxi
Cancún - Flamingo Mall
Cancún - Cancún International Airport (Terminal 2)
Cancún - Cancún International Airport (Terminal 3)
Charleston - Downtown
Chicago - Navy Pier
Daytona Beach - Ocean Walk Shoppes
Denver - Downtown
Destin - Beachfront
Ft. Lauderdale - Beachfront
Galveston - Galveston Island Historic Pleasure Pier
Gatlinburg - Gatlinburg Convention Center
Universal Studios Hollywood - Universal CityWalk
Hong Kong - Peak Tower
Honolulu - Ala Moana Center
Indonesia - Bali
Kailua Kona - Ali'i Drive
Kemah - Kemah Boardwalk
Kuta - Kartika Plaza
Las Vegas - Las Vegas Strip
Laughlin - Golden Nugget Laughlin
London - London Trocadero
Long Beach - Aquarium of the Pacific
Madeira Beach - John's Pass (Largest Bubba Gump's location worldwide)
Makati - Greenbelt (Ayala Center)
Bloomington - Mall of America
Lahaina - Oceanfront
Miami - Biscayne Boulevard
Monterey - Cannery Row
Mutiara Damansara - The Curve
New Orleans - Decatur Street, French Quarter
New York City - Times Square
Orlando - Universal CityWalk
Osaka - Universal CityWalk
Puerto Vallarta - Licenciado Gustavo Díaz Ordaz International Airport
Saipan - Garapan
San Francisco - Pier 39
Santa Monica - Santa Monica Pier
Tokyo - LaQua
Toyosu - LaLaport

text: Employee social media policy[edit]

text: In 2013, a former Bubba Gump employee claimed that the social media policy in the company's employee handbook had a restrictive effect on employees’ rights by prohibiting them from discussing their jobs online.[6] In 2015, a National Labor Relations Board administrative law judge ruled that Bubba Gump did not violate employees’ rights as they did not explicitly prohibit employees from discussing job-related subjects, but only expected them to do so in a civil manner. [7] There have been many cases in the last few years in which the National Labor Relations Board found companies social media policies to be overbroad and ruled in favor of the employee(s).[8]

text: Notable employees[edit]

text: Actor Chris Pratt was discovered in 2000 while working as a waiter at the Bubba Gump Shrimp Co. in Maui, Hawaii.[9] He waited on the table of actor/director Rae Dawn Chong, who had starred in one of Pratt's favorite films, Commando. Chong offered Pratt a role in a short movie she was directing at the time.


document_title: Tesla Autopilot

question_text: when did tesla start making self driving cars

text: Tesla Autopilot

text: History[edit]

text: Autopilot was first offered on October 9, 2014, for Tesla Model S, followed by the Model X upon its release.[5] Autopilot was included within a "Tech Package" option. At that time Autopilot features included semi-autonomous drive and parking capabilities.[6][7][8] Initial versions of Autopilot were developed in partnership with Israeli company Mobileye.[9] Tesla and Mobileye ended their partnership in July 2016.[10][11]

text: In October 2015, Tesla released Autopilot version 7.0 to its customers.[12] Autopilot Firmware 7.1 then removed some self-driving features to discourage customers from engaging in risky behavior and added Summon remote parking technology that can move the car forward and back without a driver in the car.[13][14][15]

text: On August 31, 2016, Elon Musk announced Autopilot 8.0, which processes radar signals to create a coarse point cloud similar to Lidar to help navigate in low visibility, and even to 'see' in front of the car ahead.[16][17] Autopilot version 8 uses radar as the primary sensor instead of the camera.[18] In November 2016, Autopilot 8.0 was updated to have a more noticeable signal to the driver that it is engaged and it requires drivers to touch the steering wheel more frequently.[19][20] By November 2016, Autopilot had operated actively on hardware version 1 vehicles for 300 million miles (500 million km) and 1.3 billion miles (2 billion km) in shadow mode.[21]

text: In October 2016, Tesla said all vehicles came with the necessary sensing and computing hardware, known as Hardware version 2 (HW2), for future fully autonomous operation (SAE Level 5).[22]

text: Autopilot for HW2 cars came in February 2017. It included adaptive cruise control, autosteer on divided highways, autosteer on 'local roads’ up to a speed of 35 mph or a specified number of mph over the local speed limit to a maximum of 45 mph.[23] Firmware version 8.1 for HW2 arrived in June 2017 adding a new driving-assist algorithm, full-speed braking and handling parallel and perpendicular parking.[24] Later releases offered smoother lane-keeping and less jerky acceleration and deceleration.

text: HW 2.5 was released in July 2017, appearing in cars built from August 2017.[25]

text: Hardware[edit]

text: Hardware 1[edit]

text: Vehicles manufactured after late September 2014 are equipped with a camera mounted at the top of the windshield, forward looking radar (supplied by Bosch)[26][27] in the lower grille and ultrasonic acoustic location sensors in the front and rear bumpers that provide a 360-degree view around the car. The computer is the Mobileye EyeQ3.[28] This equipment allows Model S to detect road signs, lane markings, obstacles, and other vehicles. Upgrading from Hardware 1 to Hardware 2 is not offered as it would require substantial work and cost.[29]

text: Hardware 2[edit]

text: Hardware 2, included in all vehicles manufactured after October 2016, includes an Nvidia Drive PX 2[30] GPU for CUDA based GPGPU computation.[31][32] Tesla claimed that Hardware 2 provided the necessary equipment to allow full self-driving capability at SAE Level 5. The hardware includes 8 surround cameras and 12 ultrasonic sensors, in addition to forward-facing radar with enhanced processing capabilities.[22] The Autopilot computer is replaceable to allow for future upgrades.[33] The radar is claimed to be able to observe beneath and ahead of the vehicle in front of the Tesla; the radar can see vehicles through heavy rain, fog or dust.[34] Tesla claimed that the hardware was capable of processing 200 frames per second.[35]

text:
Hardware specifications

Hardware
2014 AutopilotHardware 1
2016 Enhanced Autopilot--4 Cameras/Full Self-Driving Capability--8 Cameras[36]Hardware 2

Forward Radar
Unknown range
160 m (525 ft)

Forward Cameras
1 monochrome with unknown range
Trifocal camera:Narrow: 250 m (820 ft)--Enhanced Autopilot and Full Self-Driving Capability.Main: 150 m (490 ft)--Enhanced Autopilot and Full Self-Driving Capability.Wide:  60 m (195 ft)--Full Self-Driving Capability.

Forward Looking Side Cameras
N/A
Left: 80 m (260 ft)--Full Self-Driving CapabilityRight: 80 m (260 ft)--Full Self-Driving Capability

Rearward Looking Side Cameras
N/A
Left: 100 m (330 ft)--Enhanced Autopilot and Full Self-Driving Capability.Right: 100 m (330 ft)--Enhanced Autopilot and Full Self-Driving Capability.

Rear View Camera
For human use, not for automation use
50 m (165 ft)--Full Self-Driving Capability

Sonars
12 surrounding with 5 m (16 ft) range
12 surrounding with 8 m (26 ft) range

Platform

MobilEye EyeQ3[37]

NVIDIA DRIVE PX 2 AI computing platform[38]

text:
Function specifications (pending incremental updates and regulatory approvals)

Functions

2014 Autopilot
Hardware 1

2016 Enhanced Autopilot/Full Self-Driving Capability
Hardware 2

Hands-on feature with limited Hands-Free On-Ramp to Off-Ramp for limited-access roads

Yes, except when driver wants to change lane.[39]

Yes[40]

TACC-Traffic-Aware Cruise Control (Smart/Adaptive Cruise Control)

Yes[41]

Yes[40]

Max speed

90 mph (145 km/h)[42]

90 mph (145 km/h)[43]

Autosteer

Yes[41]

Yes, and in the future: tighter, more complex roads[44]

Auto Lane Change

Driver initiates the lane changing signal when the traffic is safe (due to ultrasonic 16 foot limited range capability) then the system does the rest.[45]

Now : Driver initiates the lane changing signal
In the future :
Automatically done all by itself for a faster lane and without driver's judgement nor input.[44]

Highway Interchanges

Manual by using turn signal[46]

In future: Yes[44]

Autopark:  Parallel and Perpendicular Parking

Yes[41]

Yes[40]

Summon (remote automatic car retrieval, including automatic garage door opening and closing)

Yes[47]

Yes[40]

Lane Departure Warning

Yes[48]

Yes[49]

Full Self-Driving Capability

No[41]

In future: Yes, with an additional fee. The Tesla car will be able to drive itself, automatically recharge at "cable bot"-equipped Superchargers and can use Parking Seek to find a parking space all without a driver.[40]

text: Hardware 2.5[edit]

text: HW 2.5 (also known as '2.1') included a secondary node (without a GPU) to provide more computing power and wiring redundancy to slightly improve reliability.[25][50]

text: Hardware 3.0[edit]

text: HW 3.0 includes a custom Tesla-designed processor. Tesla claimed that the new system would process 2,000 frames per second. The firm described it as a "neural network accelerator".[35] The company claimed that 3.0 was necessary for "full self-driving", but not for "enhanced Autopilot" functions.[51]

text: Driving features[edit]

text: Tesla requires operators to monitor the vehicle at all times, just as the Federal Aviation Administration requires pilots to monitor aircraft on autopilot. Autopilot includes multiple capabilities, including adaptive cruise control, lane centering and lane departure warning.

text: Software updates[edit]

text: Autopilot-enabled cars receive Autopilot software updates wirelessly, the same as all other Tesla software updates.

text: Adaptive cruise control[edit]

text: Autopilot has the ability to follow another car, maintaining a safe distance from it as it speeds up and slows down. It can observe a second vehicle in front of the vehicle that it is following. It also slows on tight curves and when a car crosses the road in front of it. It can be enabled at any speed above 17 mph. By default, it sets the limit at the current speed limit plus/minus any driver-specified offset.

text: Alerts[edit]

text: Autopilot alerts the driver under various circumstances, such as a surprising situation on the road or excessive inattention by the driver. If the driver dismisses three audio warnings within an hour, Autopilot is disabled until the car is parked. This is to prevent experienced drivers from excessive reliance on built-in safety features. At speeds under 8 mph on divided highways, Autopilot functions indefinitely without the driver's hands on the wheel. Under 45 mph free hands are allowed for five minutes, unless the car detects lateral acceleration. Above 45 mph free hands are allowed for three minutes if following another vehicle or one minute without following a car.[34]

text: Autopark/Summon[edit]

text: Autopark drives the car into a parking spot, while Summon drives it out. Configuration settings control maximum distance, side clearance and bumper clearance. This feature activates Homelink to open and close garage doors and it is available using the fob or the Tesla mobile app.[52] As of March 2017, Summon was available in "beta" for HW2. Controls include bumper, side clearance and summon distance.[53]

text: Autosteer[edit]

text: Autosteer steers the car to remain in whatever lane it is in (known as lane-keeping). With HW1, it is also able to safely change lanes as directed by a tap of the turn signal.[54] As of May 2017, HW2 is limited to 90 mph (145 km/h) on highway roads and the former 35 mph (56 km/h) speed limit on non-highway roads was removed, instead limiting to five over the speed limit or 45 mph (72 km/h) if no speed limit is detected.[55]

text: Safety features[edit]

text: The Autopilot can detect a potential front or side collision with another vehicle, bicycle or pedestrian within a distance of 525 feet (160 m), if one is found it sounds a warning.[56] Autopilot has automatic emergency braking that detects objects that may hit the car and applies the brakes. Autopilot also can automatically adjust the high/low beam headlights as the nighttime lighting changes.

text: Speed assist[edit]

text: Front-facing cameras detect speed limit signs and display the current limit on the dashboard or center display. Limits are compared against GPS data if no signs are present.[56]

text: Public debate[edit]

text: Some industry experts have raised questions about the legal status of autonomous driving in the U.S. and whether Tesla owners would violate current state regulations when using the Autopilot function. The few states that have passed laws allowing autonomous cars on the road, limit their use for testing purposes; not for use by the general public. Also, there are questions about the liability for autonomous cars in case there is a mistake.[57] A Tesla spokesman said there is "nothing in our autopilot system that is in conflict with current regulations." "We are not getting rid of the pilot. This is about releasing the driver from tedious tasks so they can focus and provide better input." Google's director of self-driving cars said he does not think there is a regulatory block as long as the self-driving vehicle met crash-test and other safety standards. A spokesman for the U.S. National Highway Traffic Safety Administration (NHTSA) said that "any autonomous vehicle would need to meet applicable federal motor vehicle safety standards" and the NHTSA "will have the appropriate policies and regulations in place to ensure the safety of this type of vehicles."[57]

text: According to Elon Musk, "We really designed the Model S to be a very sophisticated computer on wheels. Tesla is a software company as much as it is a hardware company. A huge part of what Tesla is, is a Silicon Valley software company. We view this the same as updating your phone or your laptop."[58] Full autonomy is “really a software limitation: The hardware exists to create full autonomy, so it’s really about developing advanced, narrow AI for the car to operate on.“[59][60]

text: The Autopilot development focus is on "increasingly sophisticated neural nets that can operate in reasonably sized computers in the car”.[59][60] According to Musk, "the car will learn over time", including from other cars.[61]  Early data after 47 million miles of driving in Autopilot mode shows the probability of an accident is at least 50% lower when using Autopilot.[62] However, Ars Technica notes that the brake system tends to initiate later than some drivers expect.[63] One driver claimed that Tesla's Autopilot failed to brake, resulting in collisions. Tesla pointed out that the driver deactivated the cruise control of the car prior to the crash.[64] Ars Technica also notes that the lane changes are semi-automatic; the driver must activate the turn signal in order for the car to initiate a lane change.[65]

text: Tesla's Autopilot with Hardware version 1 (HW1) can be classified as somewhere between levels 2 and 3 under the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) five levels of vehicle automation. At this level, the car can act autonomously but requires the driver to be prepared to take control at a moment's notice.[66][67] HW1 is suitable only on limited-access highways, and sometimes will fail to detect lane markings and disengage itself. In urban driving the system will not read traffic signals or obey stop signs. This system also does not detect pedestrians or cyclists,[68] and while AP1 detects motorcycles,[69] there has been two instances of AP rear-ending motorcycles.[70]

text: There has been significant controversy over the media response to the fatal Tesla accident described in the below section. Whilst a significant amount of blame was apportioned to Tesla for the failure of its Autopilot system, it must be noted that the system at the time of the accident was in a beta phase and not ready for widespread public use, and also required the driver to ensure that their hands remained on the steering wheel at all times, and to be prepared to resume manual driving at any moment.[71][undue weight?  – discuss] Hence, when used as an assistive feature (as intended by Tesla), some hold the view that Autopilot can only enhance road safety,[71] assuming it does not lull the driver into complacent inattention.

text: Autopilot potentially saved the life of a pedestrian in Washington, D.C. on the night of July 17, 2016,[72][73] and played a pivotal role in a medical emergency involving 37-year-old Joshua Neally that same month.[74] Neally was driving his Tesla Model X when he suffered a pulmonary embolism that caused intense panic and rendered him incapable of driving.[75] Neally used Autopilot to drive most of the highway to a local hospital. At the off-ramp, Neally took control of the car and drove to the emergency room.[75]

text: Legal challenges[edit]

text: Tesla's Autopilot faced a class action suit brought in 2017 that claimed the second-generation Enhanced Autopilot system is "dangerously defective."[76] The suit was settled in 2018.[77]

text: Incidents[edit]

text: Handan, China (January 20, 2016)[edit]

text: On January 20, 2016, the driver of a Tesla Model S in Handan, China was killed when their car crashed into a stationary truck.[78] The Tesla was following a car in the far left lane of a multi-lane highway; the car in front moved to the right lane to avoid a truck stopped on the left shoulder, and the Tesla, which the driver's father believes was in Autopilot mode, did not slow before colliding with the stopped truck.[79] According to footage captured by a dashboard camera, the stationary street sweeper on the left side of the expressway partially extended into the far left lane, and the driver did not appear to respond to the unexpected obstacle.[80]

text: In September 2016, the media reported the driver's family had filed a lawsuit in July against the Tesla dealer who sold the car.[81] The family's lawyer stated the suit was intended "to let the public know that self-driving technology has some defects. We are hoping Tesla, when marketing its products, will be more cautious. Don’t just use self-driving as a selling point for young people."[79] Tesla released a statement which said they "have no way of knowing whether or not Autopilot was engaged at the time of the crash" since the car telemetry could not be retrieved remotely due to damage caused by the crash.[79] Telemetry was recorded locally to a SD card and was not given to Tesla, who provided a decoding key to a third party for independent review. Tesla added that "while the third-party appraisal is not yet complete, we have no reason to believe that Autopilot on this vehicle ever functioned other than as designed."[82]

text: Williston, Florida (May 7, 2016)[edit]

text: The first publicized fatal accident involving a Tesla engaged in Autopilot mode took place in Williston, Florida, on May 7, 2016. The driver was killed in a crash with a 18-wheel tractor-trailer.

text: By late June 2016, the U.S. National Highway Traffic Safety Administration (NHTSA) opened a formal investigation into the accident, working with the Florida Highway Patrol. According to the NHTSA, preliminary reports indicate the crash occurred when the tractor-trailer made a left turn in front of the Tesla at an intersection on a non-controlled access highway, and the car failed to apply the brakes. The car continued to travel after passing under the truck’s trailer.[83][84][85] The diagnostic log of the Tesla indicated it was traveling at a speed of 74 mi/h (119 km/h) when it collided with and traveled under the trailer, which was not equipped with a side underrun protection system.[86]:12 The underride collision sheared off the Tesla's glasshouse, destroying everything above the beltline, and caused fatal injuries to the driver.[86]:6–7; 13 Approximately nine seconds after colliding with the trailer, the Tesla traveled another 886.5 feet (270.2 m) and came to rest after colliding with two chain-link fences and a utility pole.[86]:7; 12

text: The NHTSA's preliminary evaluation was opened to examine the design and performance of any automated driving systems in use at the time of the crash, which involves a population of an estimated 25,000 Model S cars.[87] On July 8, 2016, the NHTSA requested Tesla Inc. to hand over to the agency detailed information about the design, operation and testing of its Autopilot technology. The agency also requested details of all design changes and updates to Autopilot since its introduction, and Tesla's planned updates scheduled for the next four months.[88]

text: According to Tesla, "neither autopilot nor the driver noticed the white side of the tractor-trailer against a brightly lit sky, so the brake was not applied." The car attempted to drive full speed under the trailer, "with the bottom of the trailer impacting the windshield of the Model S." Tesla also stated that this was Tesla’s first known Autopilot-related death in over 130 million miles (208 million km) driven by its customers while Autopilot was activated. According to Tesla there is a fatality every 94 million miles (150 million km) among all type of vehicles in the U.S.[83][84][89] It is estimated that billions of miles will need to be traveled before Tesla Autopilot can claim to be safer than humans with statistical significance (although fewer than billions of miles will be needed if Tesla Autopilot is more dangerous). Researchers say that Tesla and others need to release more data on the limitations and performance of automated driving systems if self-driving cars are to become safe and understood enough for mass market use.[90][91]

text: The truck's driver told the Associated Press that he could hear a Harry Potter movie playing in the crashed car, and said the car was driving so quickly that "he went so fast through my trailer I didn't see him." "It was still playing when he died and snapped a telephone pole a quarter mile down the road." According to the Florida Highway Patrol, they found in the wreckage an aftermarket portable DVD player. It is not possible to watch videos on the Model S touchscreen display.[85][92] A laptop computer was recovered during the post-crash examination of the wreck, along with an adjustable vehicle laptop mount attached to the front passenger's seat frame. The NHTSA concluded the laptop was probably mounted and the driver may have been distracted at the time of the crash.[86]:17–19; 21

text: In July 2016, the U.S. National Transportation Safety Board (NTSB) announced it had opened a formal investigation into the fatal accident while Autopilot was engaged. The NTSB is an investigative body that only has the power to make policy recommendations. An agency spokesman said, "It's worth taking a look and seeing what we can learn from that event, so that as that automation is more widely introduced we can do it in the safest way possible." The NTSB opens annually about 25 to 30 highway investigations.[93]  In September 2017, the NTSB released its report, determining that "the probable cause of the Williston, Florida, crash was the truck driver’s failure to yield the right of way to the car, combined with the car driver’s inattention due to overreliance on vehicle automation, which resulted in the car driver’s lack of reaction to the presence of the truck. Contributing to the car driver’s overreliance on the vehicle automation was its operational design, which permitted his prolonged disengagement from the driving task and his use of the automation in ways inconsistent with guidance and warnings from the manufacturer."[94].

text:
In January 2017, the NHTSA Office of Defects Investigations (ODI) released a preliminary evaluation, finding that the driver in the crash had seven seconds to see the truck and identifying no defects in the Autopilot system; the ODI also found that the Tesla car crash rate dropped by 40 percent after Autosteer installation,[95][96] but later also clarified that it did not assess the effectiveness of this technology or whether it was engaged in its crash rate comparison.[97] The NHTSA Special Crash Investigation team published its report in January 2018.[86] According to the report, for the drive leading up to the crash, the driver engaged Autopilot for 37 minutes and 26 seconds, and the system provided 13 "hands not detected" alerts, to which the driver responded after an average delay of 16 seconds.[86]:24 The report concluded "Regardless of the operational status of the Tesla’s ADAS technologies, the driver was still responsible for maintaining ultimate control of the vehicle. All evidence and data gathered concluded that the driver neglected to maintain complete control of the Tesla leading up to the
crash."[86]:25

text: Culver City, California (January 22, 2018)[edit]

text: On January 22, 2018, a Tesla Model S crashed into a fire truck parked on the side of the I-405 freeway in Culver City, California while traveling at a speed exceeding 50 mph (80 km/h) and the driver survived.[98] The driver said he was using Autopilot, according to the Culver City Fire Department, which reported the crash over Twitter at approximately 8:30 A.M. The fire truck and a California Highway Patrol vehicle were parked in the left emergency lane and carpool lane of the southbound 405, blocking off the scene of an earlier accident, with emergency lights flashing.[99]

text: Autopilot may not detect stationary vehicles at highway speeds and it cannot detect some objects.[100] Other advanced driver-assistance systems have similar limitations. Raj Rajkumar, who studies autonomous driving systems at Carnegie Mellon University, believes the radars used for Autopilot are designed to detect moving objects, but are "not very good in detecting stationary objects".[101] Both NTSB and NHTSA have dispatched teams to investigate the crash.[102] Hod Lipson, director of Columbia University's Creative Machines Lab, faulted the diffusion of responsibility concept: "If you give the same responsibility to two people, they each will feel safe to drop the ball. Nobody has to be 100%, and that's a dangerous thing."[103]

text: Mountain View, California (March 23, 2018)[edit]

text: On March 23, 2018, a second US Autopilot fatality occurred in Mountain View, California.[104] The crash occurred just before 9:30 A.M. on southbound US 101 at the carpool lane exit for southbound Highway 85, at a concrete barrier where the left-hand offramp separates from 101. After the Model X crashed into the narrow concrete barrier, it was struck again by two following vehicles, and then it caught on fire.[105]

text: Both the NHTSA and NTSB are investigating the March 2018 crash.[106] Another driver of a Model S demonstrated that Autopilot appeared to be confused by the road surface marking in April 2018. The gore ahead of the barrier is marked by diverging solid white lines (a vee-shape); the Autosteer feature of the Model S appeared to mistakenly use the left-side white line instead of the right-side white line as the lane marking for the far left lane, which would have led the Model S into the same concrete barrier had the driver not taken control.[107] Ars Technica concluded "that as Autopilot gets better, drivers could become increasingly complacent and pay less and less attention to the road."[108]

text: In a corporate blog post, Tesla noted the impact attenuator separating the offramp from US 101 had been previously crushed and not replaced prior to the Model X crash on March 23.[104][109] The post also stated that Autopilot was engaged at the time of the crash, and the driver's hands had not been detected manipulating the steering wheel for six seconds before the crash. Vehicle data showed the driver had five seconds and 150 metres (490 ft) "unobstructed view of the concrete divider, [...] but the vehicle logs show that no action was taken."[104] The NTSB investigation had been focused on the damaged impact attenuator and the vehicle fire after the collision, but after it was reported the driver had complained about the Autopilot functionality,[110] the NTSB announced it would also investigate "all aspects of this crash including the driver’s previous concerns about the autopilot."[111] A NTSB spokesman stated the organization "is unhappy with the release of investigative information by Tesla".[112] Elon Musk dismissed the criticism, tweeting that NTSB was "an advisory body" and that "Tesla releases critical crash data affecting public safety immediately & always will. To do otherwise would be unsafe."[113] In response, NTSB removed Tesla as a party to the investigation on April 11.[114]

text: NTSB released a preliminary report on June 7, 2018, which provided the recorded telemetry of the Model X and other factual details. Autopilot was engaged continuously for almost nineteen minutes prior to the crash. In the minute before the crash, the driver's hands were detected on the steering wheel for 34 seconds in total, but his hands were not detected for the six seconds immediately preceding the crash. Seven seconds before the crash, the Tesla began to steer to the left and was following a lead vehicle; four seconds before the crash, the Tesla was no longer following a lead vehicle; and during the three seconds before the crash, the Tesla's speed increased to 70.8 mi/h (113.9 km/h). The driver was wearing a seatbelt, and was pulled from the vehicle before it was engulfed in flames. The crash attenuator had been previously damaged on March 12 and had not been replaced at the time of the Tesla crash.[115]

text: South Jordan, Utah (May 11, 2018)[edit]

text: On May 11, 2018, a Tesla Model S with Autopilot engaged crashed into the rear of a fire truck that was stopped at a red light in South Jordan, Utah. The Tesla was moving at an estimated 60 mi/h (97 km/h) and did not appear to brake or attempt to avoid the impact, according to witnesses.[116] The driver of the Tesla, who survived the impact with a broken foot, admitted she was looking at her phone before the crash.[117]It did not stop because Autopilot can not detect stationary vehicles at highway speeds and it cannot detect some objects.[100] Other advanced driver-assistance systems have similar limitations. Raj Rajkumar, who studies autonomous driving systems at Carnegie Mellon University, believes the radars used for Autopilot are designed to detect moving objects, but are "not very good in detecting stationary objects".[101] Both NTSB and NHTSA have dispatched teams to investigate the crash.[102] Hod Lipson, director of Columbia University's Creative Machines Lab, faulted the diffusion of responsibility concept: "If you give the same responsibility to two people, they each will feel safe to drop the ball. Nobody has to be 100%, and that's a dangerous thing."[103]


document_title: Pepsin

question_text: where does pepsin work in the digestive system

text: Pepsin

text: History[edit]

text: Pepsin was one of the first enzymes to be discovered. It was discovered in 1836 by Theodor Schwann. Schwann coined its name from the Greek word πέψις pepsis, meaning "digestion" (from πέπτειν peptein "to digest").[4][5][6][7] Scientists around this time began discovering many biochemical compounds that play a significant role in biological processes, and pepsin was one of them. An acidic substance that was able to convert nitrogen-based foods into water-soluble material was determined to be pepsin.[8]

text: In 1928, it became one of the first enzymes to be crystallized when John H. Northrop crystallized it using dialysis, filtration, and cooling.[9]

text: Precursor[edit]

text: Pepsin is expressed as a zymogen called pepsinogen, whose primary structure has an additional 44 amino acids.

text: In the stomach, chief cells release pepsinogen. This zymogen is activated by hydrochloric acid (HCl), which is released from parietal cells in the stomach lining. The hormone gastrin and the vagus nerve trigger the release of both pepsinogen and HCl from the stomach lining when food is ingested. Hydrochloric acid creates an acidic environment, which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin.

text: Activity and stability[edit]

text: Pepsin is most active in acidic environments between 37 °C and 42 °C.[10][11] Accordingly, its primary site of synthesis and activity is in the stomach (pH 1.5 to 2). Pepsin will digest up to 20% of ingested amide bonds by cleaving preferentially at the N-terminal side[12]:96 of aromatic amino acids such as phenylalanine, tryptophan, and tyrosine.[12]:675 Pepsin exhibits preferential cleavage for hydrophobic, preferably aromatic, residues in P1 and P1' positions. Increased susceptibility to hydrolysis occurs if there is a sulfur-containing amino acid close to the peptide bond, which has an aromatic amino acid. Pepsin cleaves Phe1Val, Gln4His, Glu13Ala, Ala14Leu, Leu15Tyr, Tyr16Leu, Gly23Phe, Phe24 in the insulin B chain. Pepsin exhibits maximal activity at pH 2.0 and is inactive at pH 6.5 and above, however pepsin is not fully denatured or irreversibly inactivated until pH 8.0.[13] Therefore, pepsin in solution of up to pH 8.0 can be reactivated upon re-acidification. The stability of pepsin at high pH has significant implications on disease attributed to laryngopharyngeal reflux. Pepsin remains in the larynx following a gastric reflux event.[14][15] At the mean pH of the laryngopharynx (pH = 6.8) pepsin would be inactive but could be reactivated upon subsequent acid reflux events resulting in damage to local tissues.

text: In laryngopharyngeal reflux[edit]

text: Pepsin is one of the primary causes of mucosal damage during laryngopharyngeal reflux.[16][17] Pepsin remains in the larynx (pH 6.8) following a gastric reflux event.[14][15] While enzymatically inactive in this environment, pepsin would remain stable and could be reactivated upon subsequent acid reflux events.[13] Exposure of laryngeal mucosa to enzymatically active pepsin, but not irreversibly inactivated pepsin or acid, results in reduced expression of protective proteins and thereby increases laryngeal susceptibility to damage.[13][14][15]

text: Pepsin may also cause mucosal damage during weakly acidic or non-acid gastric reflux. Weak or non-acid reflux is correlated with reflux symptoms and mucosal injury.[18][19][20][21] Under non-acid conditions (neutral pH), pepsin is internalized by cells of the upper airways such as the larynx and hypopharynx by a process known as receptor-mediated endocytosis.[22] The receptor by which pepsin is endocytosed is currently unknown. Upon cellular uptake, pepsin is stored in intracellular vesicles of low pH at which its enzymatic activity would be restored. Pepsin is retained within the cell for up to 24 hours.[23] Such exposure to pepsin at neutral pH and endoyctosis of pepsin causes changes in gene expression associated with inflammation, which underlies signs and symptoms of reflux,[24] and tumor progression.[25] This and other research[26] implicates pepsin in carcinogenesis attributed to gastric reflux.

text: Pepsin in airway specimens is considered to be a sensitive and specific marker for laryngopharyngeal reflux.[27][28] Research to develop new pepsin-targeted therapeutic and diagnostic tools for gastric reflux is ongoing. A rapid non-invasive pepsin diagnostic called Peptest is now available which determines the presence of pepsin in saliva samples.[29]

text: Storage[edit]

text: Pepsins should be stored at very low temperatures (between −80 °C and −20 °C) to prevent autolysis (self-digestion).

text: Inhibitors[edit]

text: Pepsin may be inhibited by high pH (see "Activity" and "Stability", above) or by inhibitor compounds. Pepstatin is a low molecular weight compound and potent inhibitor specific for acid proteases with a Ki of about 10−10 M for pepsin. The statyl residue of pepstatin is thought to be responsible for pepstatin inhibition of pepsin; statine is a potential analog of the transition state for catalysis by pepsin and other acid proteases. Pepstatin does not covalently bind pepsin and inhibition of pepsin by pepstatin is therefore reversible.[30] 1-bis(diazoacetyl)-2-phenylethane reversibly inactivates pepsin at pH 5, a reaction which is accelerated by the presence of Cu(II).[31]

text: Pepsin also undergoes feedback inhibition; a product of protein digestion slows down the reaction by inhibiting pepsin.[32][33]

text: Sucralfate also inhibits pepsin activity.

text: Applications[edit]

text: Commercial pepsin is extracted from the glandular layer of hog stomachs. It is a component of rennet used to curdle milk during the manufacture of cheese. Pepsin is used for a variety of applications in food manufacturing: to modify and provide whipping qualities to soy protein and gelatin,[34] to modify vegetable proteins for use in nondairy snack items, to make precooked cereals into instant hot cereals,[35] and to prepare animal and vegetable protein hydrolysates for use in flavoring foods and beverages. It is used in the leather industry to remove hair and residual tissue from hides and in the recovery of silver from discarded photographic films by digesting the gelatin layer that holds the silver.[36] Pepsin was historically an additive of Beemans gum brand chewing gum by Dr. Edward E. Beeman.

text: Pepsin is commonly used in the preparation of F(ab')2 fragments from antibodies. In some assays, it is preferable to use only the antigen-binding (Fab) portion of the antibody. For these applications, antibodies may be enzymatically digested to produce either an Fab or an F(ab')2 fragment of the antibody. To produce an F(ab')2 fragment, IgG is digested with pepsin, which cleaves the heavy chains near the hinge region.[37] One or more of the disulfide bonds that join the heavy chains in the hinge region are preserved, so the two Fab regions of the antibody remain joined together, yielding a divalent molecule (containing two antibody binding sites), hence the designation F(ab')2. The light chains remain intact and attached to the heavy chain. The Fc fragment is digested into small peptides. Fab fragments are generated by cleavage of IgG with papain instead of pepsin. Papain cleaves IgG above the hinge region containing the disulfide bonds that join the heavy chains, but below the site of the disulfide bond between the light chain and heavy chain. This generates two separate monovalent (containing a single antibody binding site) Fab fragments and an intact Fc fragment. The fragments can be purified by gel filtration, ion exchange, or affinity chromatography.[38]

text: Fab and F(ab')2 antibody fragments are used in assay systems where the presence of the Fc region may cause problems. In tissues such as lymph nodes or spleen, or in peripheral blood preparations, cells with Fc receptors (macrophages, monocytes, B lymphocytes, and natural killer cells) are present which can bind the Fc region of intact antibodies, causing background staining in areas that do not contain the target antigen. Use of F(ab')2 or Fab fragments ensures that the antibodies are binding to the antigen and not Fc receptors. These fragments may also be desirable for staining cell preparations in the presence of plasma, because they are not able to bind complement, which could lyse the cells. F(ab')2, and to a greater extent Fab, fragments allow more exact localization of the target antigen, i.e., in staining tissue for electron microscopy. The divalency of the F(ab')2 fragment enables it to cross-link antigens, allowing use for precipitation assays, cellular aggregation via surface antigens, or rosetting assays.[39]

text: Genes[edit]

text: The following three genes encode identical human pepsinogen A enzymes:

text:
pepsinogen 3, group I (pepsinogen A)

Identifiers

Symbol
PGA3

Entrez
643834

HUGO
8885

OMIM
169710

RefSeq
NM_001079807

UniProt
P00790

Other data

EC number
3.4.23.1

Locus
Chr. 11 q13

pepsinogen 4, group I (pepsinogen A)

Identifiers

Symbol
PGA4

Entrez
643847

HUGO
8886

OMIM
169720

RefSeq
NM_001079808

UniProt
P00790

Other data

EC number
3.4.23.1

Locus
Chr. 11 q13

pepsinogen 5, group I (pepsinogen A)

Identifiers

Symbol
PGA5

Entrez
5222

HUGO
8887

OMIM
169730

RefSeq
NM_014224

UniProt
P00790

Other data

EC number
3.4.23.1

Locus
Chr. 11 q13

text: A fourth human gene encodes gastricsin also known as pepsinogen C:

text:
progastricsin
(pepsinogen C)

Identifiers

Symbol
PGC

Entrez
5225

HUGO
8890

OMIM
169740

RefSeq
NM_001166424

UniProt
P20142

Other data

EC number
3.4.23.3

Locus
Chr. 6 pter-p21.1