Cnidaria

Cnidaria (/nɪˈdɛəriə, naɪ-/) is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.

Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick.

Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually, but many species have complex life cycles of asexual polyp stages and sexual medusae stages. Some, however, omit either the polyp or the medusa stage, and the parasitic classes evolved to have neither form.

Cnidarians were formerly grouped with ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: the almost wholly sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa (jellyfish); Cubozoa (box jellies); and Hydrozoa (a diverse group that includes all the freshwater cnidarians as well as many marine forms, and has both sessile members, such as Hydra, and colonial swimmers, such as the Portuguese man o' war). Staurozoa have recently been recognised as a class in their own right rather than a sub-group of Scyphozoa, and the highly derived parasitic Myxozoa and Polypodiozoa were firmly recognized as cnidarians in 2007.

Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from dinoflagellates, and a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish, turtles, and even other cnidarians. Many scleractinian corals—which form the structural foundation for coral reefs—possess polyps that are filled with symbiotic photo-synthetic zooxanthellae. While reef-forming corals are almost entirely restricted to warm and shallow marine waters, other cnidarians can be found at great depths, in polar regions, and in freshwater.

Recent phylogenetic analyses support monophyly of cnidarians, as well as the position of cnidarians as the sister group of bilaterians. Fossil cnidarians have been found in rocks formed about , and other fossils show that corals may have been present shortly before and diversified a few million years later. However, molecular clock analysis of mitochondrial genes suggests a much older age for the crown group of cnidarians, estimated around , almost 200 million years before the Cambrian period, as well as any fossils.

## Distinguishing features

Cnidarians form a phylum of animals that are more complex than sponges, about as complex as ctenophores (comb jellies), and less complex than bilaterians, which include almost all other animals. 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 usually used mainly to capture prey. In some species, cnidocytes can also be used as anchors. Cnidarians are also distinguished by the fact that they have only one opening in their body for ingestion and excretion i.e. they do not have a separate mouth and anus.

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. However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer. As a result, some recent text books classify ctenophores as triploblastic, and it has been suggested that cnidarians evolved from triploblastic ancestors.

## Description

### Basic body forms

Most adult cnidarians appear as either free-swimming medusae or sessile polyps, and many hydrozoans 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.

### Skeletons

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.

In some colonial polyps, a chitinous epidermis 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.

### Main cell layers

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:

- Epitheliomuscular cells whose bodies form part of the epithelium but whose bases extend to form muscle fibers in parallel rows. 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.
- Cnidocytes, the harpoon-like "nettle cells" that give the phylum Cnidaria its name. These appear between or sometimes on top of the muscle cells.
- Nerve cells. Sensory cells appear between or sometimes on top of the muscle cells, and communicate via synapses (gaps across which chemical signals flow) with motor nerve cells, which lie mostly between the bases of the muscle cells. Some form a simple nerve net.
- 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.

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.

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

### Polymorphism

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. In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks. 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.

### Cnidocytes

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:

- Nematocysts inject venom into prey, and usually have barbs to keep them embedded in the victims. Most species have nematocysts.
- 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.

The main components of a cnidocyte are:

- 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")
- 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.

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:

- 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).

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.

### Locomotion

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.

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.

### Nervous system and senses

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. 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. 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.

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.

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. 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.

### Feeding and excretion

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. Cnidaria give their symbiotic algae carbon dioxide, some nutrients, and protection against predators.

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. Their digestion is both intra and extracellular.

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. 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.

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.

### Respiration

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.

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.

### Regeneration

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.

## Reproduction

### Sexual

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.

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) 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.

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 and Laodicea undulata) and Scyphozoa (Aurelia sp.1). Anthozoa have no medusa stage at all and the polyps are responsible for sexual reproduction.

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.

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). The larvae, called planulae, swim or crawl by means of cilia. 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.

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.

### Asexual

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.

### DNA repair

Two classical DNA repair pathways, nucleotide excision repair and base excision repair, are present in hydra, and these repair pathways facilitate unhindered reproduction. The identification of these pathways in hydra is based, in part, on the presence in the hydra genome of genes homologous to genes in other genetically well studied species that have been demonstrated to play key roles in these DNA repair pathways.

## Classification

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: 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.

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.

The Myxozoa, microscopic parasites, were first classified as protozoans. Research then found that Polypodium hydriforme, a non-Myxozoan parasite within the egg cells of sturgeon, is closely related to the Myxozoa and suggested that both Polypodium and the Myxozoa were intermediate between cnidarians and bilaterian animals. More recent research demonstrates 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.

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

Current classification according to the World Register of Marine Species:

- 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 Grassé, 1970 — obligate parasites
- class Polypodiozoa Raikova, 1994 — (uncertain status)
- class Scyphozoa Goette, 1887 — "true" jellyfishes
- class Staurozoa Marques & Collins, 2004 — stalked jellyfishes

## Ecology

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 (33,000 ft) 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 and 28 °C (68 and 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. Cnidarians range in size from a mere handful of cells for the parasitic myxozoans through Hydra'''s length of 5–20 mm (1⁄4–3⁄4 in), to the Lion's mane jellyfish, which may exceed 2 m (6 ft 7 in) in diameter and 75 m (246 ft) in length.

Prey of cnidarians ranges from plankton to animals several times larger than themselves. Some cnidarians are parasites, mainly on jellyfish but a few are major pests of fish. Others obtain most of their nourishment from endosymbiotic algae or dissolved nutrients. Predators of cnidarians include: sea slugs, flatworms and comb jellies, which can incorporate nematocysts into their own bodies for self-defense (nematocysts used by cnidarian predators are referred to as kleptocnidae); starfish, notably the crown of thorns starfish, which can devastate corals; butterfly fish and parrot fish, which eat corals; and marine turtles, which eat jellyfish. Some sea anemones and jellyfish have a symbiotic relationship with some fish; for example clownfish live among the tentacles of sea anemones, and each partner protects the other against predators.

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. 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.

## Evolutionary history

### Fossil record

The earliest widely accepted animal fossils are rather modern-looking cnidarians, possibly from around , although fossils from the Doushantuo Formation can only be dated approximately. 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. Their presence implies that the cnidarian and bilaterian lineages had already diverged. Although the Ediacaran fossil Charnia used to be classified as a jellyfish or sea pen, more recent study of growth patterns in Charnia and modern cnidarians has cast doubt on this hypothesis, leaving the Canadian polyp Haootia and the British Auroralumina as the only recognized cnidarian body fossils from the Ediacaran. Auroralumina is the earliest known animal predator. Few fossils of cnidarians without mineralized skeletons are known from more recent rocks, except in lagerstätten that preserved soft-bodied animals.

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

### Family tree

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.

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. 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.

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.

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.

In molecular phylogenetics analyses from 2005 onwards, important groups of developmental genes show the same variety in cnidarians as in chordates. 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.

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

## Interaction with humans

Jellyfish stings killed about 1,500 people in the 20th century, 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.

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. 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. 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. Coral, mainly from the Pacific Ocean has long been used in jewellery, and demand rose sharply in the 1980s.

Some large jellyfish species of the Rhizostomae order are commonly consumed in Japan, Korea and Southeast Asia. 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. 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.

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. Seven other box jellies can cause a set of symptoms called Irukandji syndrome, which takes about 30 minutes to develop, and from a few hours to two weeks to disappear. Hospital treatment is usually required, and there have been a few deaths.

A number of the parasitic Myxozoans are commercially important pathogens in salmonid aquaculture. A Scyphozoa species – Pelagia noctiluca – and a Hydrozoa – Muggiaea atlantica'' – have caused repeated mass mortality in salmon farms over the years around Ireland. A loss valued at £1 million struck in November 2007, 20,000 died off Clare Island in 2013 and four fish farms collectively lost tens of thousands of salmon in September 2017.

Aquatic animal phylum having cnydocytes


Harry and the Potters

Harry and the Potters are an American rock band known for spawning the genre of wizard rock. Founded in Norwood, Massachusetts, in 2002, the group is primarily composed of brothers Joe and Paul DeGeorge, who both perform under the persona of the title character from the Harry Potter book series. Harry and the Potters are known for their elaborate live performances, and have developed a cult following within the Harry Potter fandom.

The band is often backed up by musicians like Ernie Kim, Andrew MacLeay, Brad Mehlenbacher, John Clardy, Mike Gintz, Jacob Nathan, Ben Macri, Phillip Dickey, Jason Anderson and Zach Burba. Most of them played drums. The band's most recent songs feature drummer Mike Harpring and bassist Paul Baribeau.

Since 2002, Harry and the Potters have released three studio albums, five extended plays, and a single. The duo founded the independent record label Eskimo Laboratories, and appeared in the documentary films We Are Wizards and Wizard Rockumentary. They also co-founded charity organization The Harry Potter Alliance, and formed the Wizard Rock EP of the Month Club, an extended play syndicate.

## History

### Formation (2002)

The origins were quite accidental. In Cambridge, MA, Paul DeGeorge (born (1979-06-10) June 10, 1979 (age 44)) was developing vaccines for a biotech firm as a chemical engineer. Paul had recently graduated from Tufts University. Outside the lab, Paul was a musician whose indie band—The Secrets—had toured in the northeast from 2001 to 2002. To promote his band, Paul co-founded a small indie label called Eskimo Laboratories. One of the other bands in Eskimo’s stable of talent included an act called Ed in the Refridgerators  [sic], which was fronted by Paul's 14-year-old brother Joe. Joe DeGeorge (born (1987-07-04) July 4, 1987 (age 36)) was a student at Norwood High School. He and his school friend Andrew MacLeay (A.K.A. Shaggy) had been playing in rock bands together since they were 11 and 12 years old.

A couple of years earlier after reading the Harry Potter books, Paul formulated the premise for Harry and the Potters where the principal Harry Potter characters would be the musicians: Harry as the front man, Ron on guitar, Hermione on bass and Hagrid on drums. Then a crisis of sorts struck the brothers on June 22, 2002. During a barbecue at the DeGeorge family’s Norwood Massachusetts, home, Joe organized a concert in his backyard featuring Ed and the Refridgerators, the Secrets, and Soltero. However, the latter two bands canceled the day of the event. To rescue a nearly lost opportunity, while waiting hopefully for a band to show, Harry and the Potters came into existence over the next hour when the two brothers wrote seven Potter-themed songs. They performed that first concert as Harry and the Potters for six people who remained of their audience. Of those seven backyard songs, five were to make it onto the band's first album in 2003.

### Harry and the Potters and Voldemort Can't Stop the Rock! (2003–04)

After recruiting drummer Ernie Kim, the band recorded their eponymous debut album over a weekend in the DeGeorge family living room. Released in June 2003 under the Eskimo Laboratories record label, the album contains six of the seven songs composed on June 22, 2002, and another twelve written spontaneously and immediately thereafter recorded. In "the summer of" 2003, Harry and the Potters set out on an American tour, performing at libraries. The fifth Harry Potter book – Harry Potter and the Order of the Phoenix – came out that summer and on June 21, 2003, the highly anticipated day of release, the band played five sets in a span of 24 hours. The library gigs drew crowds of mostly children and their parents. The brothers played a show at the library in Dorchester, Massachusetts, that August where they noticed the children in the audience singing along. Joe said, "Paul forgot the words to one of the songs. [The kids] were like, 'You sang it wrong!'" Paul said, "They'd be like, 'Hey, why'd you skip that song?' because they knew the exact sequence of the album." The DeGeorge brothers quickly developed an onstage persona of dressing in the fashion of wizard-school Hogwarts: white shirts under gray crew-neck sweaters, red-and-yellow striped ties, and wire-rim glasses. In a show of quirky egalitarianism, both brothers play the role of Harry Potter and dress almost identically; Paul is older and to conform to the character’s persona, he is Harry of Year 7; while Joe is the Harry of Year 4.

During May and June 2004, the band worked on their next album, Voldemort Can't Stop the Rock!, in the DeGeorge family shed. Following the release, the band toured heavily. The two brothers drove 13,000 miles across the U.S. and into Canada in their "Potter Mobile", a silver 1998 Ford Windstar minivan with a black lightning bolt emblazoned on its hood. In live concerts, Paul and Joe used pre-recorded backing tracks for much of the tour, but during the second half, Joe called on his childhood friend and former bandmate Andrew MacLeay to join the band temporarily as drummer. During the Voldemort Can't Stop the Rock! tour, Paul and Joe DeGeorge received a letter from Warner Bros. that stated that the brothers were breaking copyright laws. Although Paul sent a letter to Warner Brothers in an attempt to smooth things over, Marc Brandon, the company representative, asked to speak to Paul personally. The two later settled upon a gentlemen's agreement that, in essence, would allow Harry and the Potters to continue to sell music online and tour, but all other merchandise could only be sold at live shows.

### Harry and the Potters and the Power of Love (2005–06)

The following winter, the band began their first overseas tour. In February 2005, they toured the United Kingdom – playing London, Manchester, Milton Keynes, Chester, and Liverpool – and then followed it by playing some gigs in the Netherlands to coincide with the release of the Dutch translation of Harry Potter and the Half-Blood Prince which took place in November 2005. In the Netherlands, they played one of their earliest songs "Platform Nine and 3/4" in Dutch. In late 2005, Harry and the Potters enjoyed more tongue-in-cheek critical success from respectable quarters. The web based music ’zine Pitchfork Media even hailed Harry and the Potters as having one of the best five live shows in 2005, quipping that "The Decemberists wish they could lit-rock like this." In the fall of 2005, Joe entered Clark University in Worcester, Massachusetts. While Harry and the Potters play infrequently at rock clubs and other venues—a Yule Ball at the Middle East Downstairs in Cambridge, Massachusetts, in December 2005 attracted an audience of 600 with 200 turned away at the door

The previous year was the watershed when a simple joke between two brothers had developed into something they had never imagined. The band continued its odd success and toured early in the year with a new wave 'sock puppet rock band' called Uncle Monsterface who opened for in March 2006. During the summer, they embarked on their 3rd cross-country summer tour ("Summer Reading and Rocking Tour 2006"), this time accompanied by fellow wizard rock band Draco and the Malfoys. Brad Mehlenbacher from Draco and the Malfoys handled drumming duties for the Potters for the entirety of their summer tour. They returned to home recording with the Harry and the Potters and the Power of Love but with a bigger sound and with the assistance of recording veteran Kevin Micka. While in the earlier albums the band's musical style was goofy inept pop-punk, the EP Scarred for Life became musically darker reflecting the penultimate book, Harry Potter and the Half-Blood Prince, as it takes as its central conceit a Harry Potter who has started a hardcore rock band. Paul and Joe departed from their proud DIY home recording and sought a studio for Scarred for Life (as well as their split EP with the Zambonis), and consequently feel that the songs on the Scarred for Life are among their "most badass".

### Extended plays and film appearances (2007–09)

By 2007, Harry and the Potters and their unexpected fan based indie music genre of wizard rock have grown into an international phenomenon. Recently, the band has engaged in charity side-projects and activism within the Harry Potter community. In January 2007, Harry and the Potters created the Wizard Rock EP of the Month Club, a mail order subscription club that released an extended play by a different wizard rock band each month. Reflecting wizard rock's literacy focus, the club raises funds for First Book, a non-profit organization that gives children the ability to read and own their first new books. In 2007, the Club raised over \$13,000 for the organization. They released their first extended play The Enchanted Ceiling in 2007. May 2007 was also the beginning of their large 70-show summer-library tour across the US and Canada called simply "Summer Tour 2007". Like their initial year in 2003, the summer of 2007 would see the release of another Harry Potter book. Harry and the Potters scheduled the mid-point of the tour to arrive back in their home state and celebrate the July 21 midnight release of the seventh book, Harry Potter and the Deathly Hallows at Harvard Yard. The festivities became an excuse for a meet-up of a number of wizard rock bands including The Hungarian Horntails and their nemesis Draco and the Malfoys which all played to a large crowd of Harry Potter fans in the Cambridge, Massachusetts college venue. Harry and the Potters resumed their tour which finally wound-up in late August. In Vancouver on July 7, 2007, hundreds of people crowded outside the Vancouver Public Library to see Harry and the Potters. ABC News reported that the band usually charge \$5 to \$10 for tickets to their shows, though some performances are free. Harry and the Potters said 600 people turned out for a July 10, 2007 show in Portland, Oregon.

In February 2008, Harry and the Potters launched a website called "Unlimited Enthusiasm". The website led users through a series of images and eventually to a forum, which contained much speculation concerning the nature of Unlimited Enthusiasm. Unlimited Enthusiasm ended up being the name of their Summer 2008 tour alongside bands Uncle Monsterface and Math The Band. Harry and the Potters undertook a summer tour, Unlimited Enthusiasm, with Math the Band, Uncle Monsterface and Jason Anderson. One of the stops in that tour was Nerdapalooza. This fall they released a short punk rock EP, In the Cupboard as part of the Wizard Rock EP of the Month Club. Two full-length feature film projects documenting Harry and the Potters and the wizard rock movement, We Are Wizards and The Wizard Rockumentary, were released in 2008.

The band played its 500th show in June 2009 at Norwood Elementary School (MA) the founding members' hometown. The group continued the Wizard Rock EP of the Month Club in 2009, and as a member of the club, they released their third extended play The Yule Ball EP, which featured a CD and a DVD of their performance at the Fourth Annual Yule Ball.

### Further career and Lumos (2010–present)

In April 2010, the group announced a series of shows in the Midwestern United States, Scandinavia, and Ireland for July and August.

In Summer 2011, Harry and the Potters embarked on another summer tour entitled, Ride The Lightning. The tour was to the biggest since 2007, playing dates all throughout the United States. The first show was held May 25 in Portland, ME and the last show was July 31 at the Knitting Factory in New York. Drummer Jacob Nathan played with the group throughout the tour. Jacob is a member of the band 926 Main Street Apt. 2, which he formed with Joe DeGeorge and Emily Barnett while attending college at Clark University.

In 2015, Harry and the Potters released the EP Hedwig Lives for digital download, which included the tracks "The Great Motorcycle Explosion of ’97" and "Ridin' in the Night".

At a live show on March 30, 2018, the band debuted songs from their forthcoming fourth studio album that will be about The Deathly Hallows. They later announced that the album would also feature the anti-folk musician Kimya Dawson as a guest vocalist. Parts of this album were recorded in a studio, and others were recorded at the Lawrence, Kansas public library. On April 23, 2019, the band unveiled a Kickstarter to help recoup the cost of recording the album, which they revealed was named Lumos. Backers could also choose rewards that include an additional album entitled Mostly Camping, as well as a vinyl single called the "Harry Potter Boogie."

## Lyrical themes and style

Harry and the Potters couple their rough-edged music with themed lyrics, which define the band as much as the costumes. The straight-forward but quirky presentation of adolescent concerns and direness in the simplest of worries gives an easily likable quality to fans. They poke fun at awkward situations from the books. For example, in the song "The Human Hosepipe", they sing, "Maybe you shouldn't have brought up Cedric Diggory/ Because I'd rather not talk about your dead ex-boyfriends over coffee." Two other examples of the bands distinctive take on teenage angst are seen in the song "Save Ginny Weasley" where they sing, "Are you petrified of being petrified?" and the song "The Godfather." where the gothic or mock-morbid line "Why do I always think that I am going to die?" is sung to an up-beat tune.

For the Harry Potter fandom, Harry and the Potters refer to words and phrases in the books, including Hogwarts, Harry's Firebolt, Felix Felicis, the Flying Car, wizard chess, platform nine and three-quarters, The Burrow, the three-headed dog Fluffy, Mrs. Norris, the basilisk, The Marauder's Map, various spells and incantations, and the Invisibility Cloak.

Harry and the Potters with its strong persona or theme is as much a performance art project as it is a rock band. Musically, they sound much like other indie rock music with the exception that the band adheres to a novel conceit: the Harry Potter books will inspire the lyrics. As Joe said in a 2005 interview, "We try to take the themes from the books and amplify them." Their musical sound is described as "simple, catchy rock – think The White Stripes crossed with Raffi – where everyone sings along which is easy because in songs like 'Voldemort Can't Stop the Rock' the title is pretty much the only line." Another reviewer’s ear hears "a touch of the Ramones in their ultra simple lyrics."

The band is organized quite simply with Paul and Joe playing their songs in a simple basic guitar-synth-and-drums indie pop style and they sing in the semi-deadpan way; a review found the vocal delivery similar to that of They Might Be Giants. The raison d’être of the band is to put enough energy and spirit into their songs to make them fun.

The band is not musically polished. Paul has joked that, if they had known of the band’s popularity, they might have made "an effort to sing in tune. But it’s hard to anticipate that sort of thing when you’re just writing silly songs and recording them in your living room over a weekend.". While musicianship is not the strength of the band, Paul says that the fans "know we're not the best singers and keyboard players, but we're okay. And they think, well, I could do that, too. I think that’s really encouraging to people ..." Paul sees the brothers as a "bridge between this mainstream phenomena of Harry Potter and the indie rock underground. Plus, we’re also pretty strong adherents to the DIY ideal." The two brothers promote this ideal of making music independently and have fused the legions of fans on to the DIY free-for-all of indie rock and punk music, albeit of the silly kind.

The Washington Post describes the brothers as having vast quantities of both passion and ability to engage an audience: the "combination of their happy, who-cares personalities and Harry Potter fanaticism has cast a spell over book-loving teens across the country." Paul said, "the band is neither geeky nor cool but 'geeky-cool'. I think the indie-rock community at the very least realizes we're taking a very DIY approach to this."

## Campaigning and activism

In 2005 the duo co-founded the non-profit organization The Harry Potter Alliance with Andrew Slack, Seth Reibstein and Sarah Newberry, an organization that uses the Harry Potter books as a platform for inspiring real-world activism, which amongst other activities, helps "wake the world up" to the genocide in Darfur. The projects invites its members to inform their local senator to support the Darfur Accountability and Divestment Act. The Harry Potter Alliance raises awareness for these projects by holding wizard rock concerts and by selling memorabilia to help fund these campaigns.

Harry and the Potters have also collaborated the Harry Potter Alliance compilation album Rocking Out Against Voldemedia, with a song entitled "Don't Believe It". The purpose of the album was to achieve the right to free press and against media consolidation by asking site viewers to contact their member of Congress to support S 2332, the "Media Ownership Act of 2007." Paul said their third EP, the 2007 The Enchanted Ceiling was recorded in their living room.

Harry and the Potters actively promote literacy. Another example of this literary activism is the reference to Tipper Gore and the Parents Music Resource Center in the song "Voldemort Can't Stop the Rock", which contains the verse, "And we won't let the Dark Lord ruin our party/ Just like Tipper Gore tried with the PMRC."

## Legacy and influence

Harry and the Potters have influenced similar acts, such as Draco and the Malfoys, The Whomping Willows, and The Remus Lupins. Wizard rock bands generally play all-ages shows at libraries, bookstores and schools, as the promotion of reading is a hallmark of the genre. In turn, because of their active promotion of literacy, young-adult and teen librarians have been promoting the band. While Harry and the Potters would become notable for making libraries their primary venue, Joe DeGeorge did not see a future in the modest venues: "I think we thought we'd play a few libraries." Paul added, "We thought it would be short-lived. We weren't like super fans, so we didn't understand this whole (Harry Potter) subculture when we started." As The Washington Post wrote, "wizard rock is an escape into a different world – a world of non-judgmental fun where grown-ups dress as wizards, evil is vanquished by song, and reading is cool." The peculiar success of Harry and the Potters has led Paul to "sense a growing affection for us amongst other musicians" and at home. The Boston Phoenix has called Harry and the Potters the "Pink Floyd of Potterdom."

In 2005 there was a tidal wave of new wizard rock bands. The brothers' do-it-yourself musical ethos has caught on with bands forming as fellow Potter fans are picking up instruments for the first time. Like Harry and the Potters, these new bands also take on the persona, or dress as a Harry Potter-themed character. Though most fans of the music are previous fans of Harry Potter, some bands have attracted listeners outside of the Harry Potter fanbase. Paul and Joe are aware of around 200 other Harry Potter-related rock bands who at least record and post songs on the Internet. The Boston Phoenix wondered—in spite of fully booked calendars—how long wizard rock would last once there are no new stories to riff on, as their musical identity is contingent on the lasting success and popularity of a book series. "In some ways", said Paul, "we want to tie things off and consider it a done deal. We've always viewed this as a project that had a finite life and end point."

## Discography

- Harry and the Potters (2003)
- Voldemort Can't Stop the Rock! (2004)
- Harry and the Potters and the Power of Love (2006)
- Lumos (2019)

Harry Potter fandom rock band

Alternative rock groups from Massachusetts


The Blip

The Blip (also known as the Decimation and the Snap) is a major fictional event depicted in the Marvel Cinematic Universe franchise in which half of all living things in the universe, chosen at random, were exterminated by Thanos snapping his fingers while wearing the Infinity Gauntlet and wielding the Infinity Stones in 2018, and then restored in late 2023 by Bruce Banner using Infinity Stones recovered from different time periods. The Blip appears to refer to the entire event, including the elimination and restoration of the victims. It manifested in the form of the mass disintegration of individual beings into dust, while the reversal had the same dust reforming into the previously deceased individuals, who reappeared in the same location with no direct awareness of what occurred.

Aspects of the Blip have been featured in Phase Three, Four, and Five of the MCU, most notably in Avengers: Infinity War (2018), which is when the first snap occurred, and Avengers: Endgame (2019), where the second snap by Banner took place. In addition, a variety of other MCU films and television series have referenced or depicted aspects of the Blip. The consequences of the Blip were substantial and far-reaching. Some were portrayed for comic effects, such as "blipped" school band members reappearing in the middle of a basketball game and "blipped" characters now being years younger than their own "unblipped" previously younger siblings. Others were portrayed for dramatic effect, such as blipped characters returning to general chaos and confusion, finding that loved ones had died in their absence, their homes and life savings were repossessed, and their jobs had been filled by others.

The Blip inspired the creation of a real-world event on the website Reddit, in which a randomly-selected half of the members of a highly popular subreddit would be banned, simulating the effects of the Blip. The ban of over 300,000 accounts, which included Infinity War co-director Anthony Russo, was the largest in Reddit's history. The Blip, as an event within the MCU, has been compared to the COVID-19 pandemic, as something that has a sustained effect on people all over the world. Since the Blip in Infinity War, many scientific articles have been published analyzing various aspects of the event, including whether it would even be possible for Thanos to snap his fingers while wearing the Infinity Gauntlet.

## Etymology

Following the release of Avengers: Infinity War, the event was dubbed by fans as "the Snap", "the Snappening", or "the Snapture". In the tie-in novel Marvel's Avengers: Infinity War: The Cosmic Quest Volume Two: Aftermath by Brandon T. Snider, the event was referred to as "the Decimation", but this naming was not used in any other related media. The event was referred to as "the Blip" in Spider-Man: Far From Home (2019), but Kevin Feige later clarified that "the Snap" referred to Thanos' finger snap in Avengers: Infinity War while "the Blip" referred to Bruce Banner's finger snap in Avengers: Endgame. Despite Feige's comments, both events were collectively referred to as "the Blip" in MCU projects such as WandaVision (2021) and The Falcon and the Winter Soldier (2021), and the term also appears to reference the five-year gap between the two snaps during which half of Earth's population was wiped from existence. Secret Invasion (2023) uses both "the Blip" and "the Snap".

## Known victims and survivors

### Victims

The Blip wiped out 50% of all living creatures. Memorials to the "vanished" victims were erected in communities across the universe. Among the victims were:

### Survivors

Those known to have survived the Blip include:

- Ajak
- Bruce Banner
- Clint Barton
- Kate Bishop
- Sharon Carter
- Carol Danvers
- Brad Davis
- Druig
- Wilson Fisk
- Gilgamesh
- Roger Harrington
- Tyler Hayward
- Happy Hogan
- Howard the Duck
- Ikaris
- Kingo
- Korg
- Cassie Lang
- Scott Lang
- Maya Lopez
- William Lopez
- Makkari
- M'Baku
- Miek
- Nakia
- Karli Morgenthau
- Nebula
- Okoye
- Christine Palmer
- Phastos
- Pepper Potts
- Maria Rambeau
- Ramonda
- James Rhodes
- Rocket
- Steve Rogers
- Natasha Romanoff
- Sersi
- Sprite
- Tony Stark
- Marc Spector
- Toussaint / T'Challa II
- Talos
- Thanos
- Thena
- Thor
- Valkyrie
- Varra / Priscilla Fury
- Wong

Scott Lang was in the Quantum Realm at the time of the Blip, and although only a few hours passed there from his perspective when he escaped from the Quantum Realm, because time passes slower there, five years had passed everywhere else. However, Lang was believed to have been a victim, due to his absence over those five years. The Eternals also survived the Blip due to them being artificial and not biological beings.

## Depictions

### Infinity Saga

In Avengers: Infinity War, Thanos obtains the six Infinity Stones and places them within a Gauntlet built by Eitri, so that he can snap his fingers and eliminate half of all life in the universe, which he believes will bring a balance that will prevent greater catastrophes from fighting over resources. The Blip occurs at the end of the film in Wakanda, where numerous characters are blipped, including Bucky Barnes, Nick Fury, Maria Hill, Wanda Maximoff, Peter Parker, Stephen Strange, T'Challa, Sam Wilson, Peter Quill, Groot, Drax, and Mantis. The Russo brothers also revealed that, despite not appearing in Infinity War, Betty Ross and Sif were blipped as well.

In a mid-credits scene in Ant-Man and the Wasp (2018), Hank Pym, Hope van Dyne, and Janet van Dyne are blipped, leaving Scott Lang stranded in the Quantum Realm. In a subsequent post-credits scene, a nationwide broadcast of the Emergency Alert System is shown on a television in Lang's home. In a post-credits scene of Captain Marvel (2019), the Avengers are surveying reports of worldwide population losses at the Avengers Compound, when Carol Danvers abruptly appears, having received a distress signal from Fury that he sent through a pager before he blipped.

When asked how the sixth season of Agents of S.H.I.E.L.D., set one year after the events of the fifth season and Infinity War, would connect to the then-upcoming Avengers: Endgame, Marvel Television head Jeph Loeb suggested in March 2019 that the one-year time jump between the previous season of the series and this one was part of the series's tie-in to that film. After Endgame was released in April, the showrunners and Loeb revealed that the series would not directly depict or reference the Blip for several reasons. They began production on the season without knowing all of Endgame's plot or how Far From Home would be depicting a post-Endgame MCU. They were also unsure when the season would be released in relation to Endgame and how much they would be allowed to reveal if they had begun airing before the film was released. They wanted to focus on telling their own story rather than be "shackled too much to the universe-changing events from the films". While acknowledging that this meant the series seemingly no longer lined up with the films' timeline, producer Jed Whedon stated that the writers had an explanation for this that made sense to them even though they did not plan to "burden the audience" with it. A line referencing the Blip and how the Quantum Realm could be used to avoid it was filmed for the series finale but was ultimately cut from the aired episode.

In Avengers: Endgame, Clint Barton's family, Erik Selvig, Shuri, and Jane Foster are confirmed to have been blipped. In the Avengers Compound, Sharon Carter and Scott Lang are also listed as blipped, though Carter went rogue to establish her identity as the Power Broker in Madripoor and Lang was unaccounted for due to being trapped in the Quantum Realm.

Some of the surviving heroes travel to the planet where Thanos has gone to attempt to recover the Infinity Stones and undo the Blip, only to learn that Thanos had destroyed the Stones to ensure that his work could not be undone. Five years later, the effects of the disappearances are explored, with many characters having experiences resulting from the event. For example, Barton is distraught at the loss of his family and becomes a rogue warrior, travelling the world to massacre organized crime figures involved in the drug trade and child trafficking. Steve Rogers leads a support group for those dealing with the loss of loved ones in the Blip. Thor, who blames himself for failing to kill Thanos before the initial snap, becomes an out-of-shape alcoholic. Urban decay is apparent in cities such as New York City and San Francisco. Carol Danvers tells the Avengers that the chaos happening on Earth is also occurring on other planets throughout the cosmos.

In the meantime, Scott Lang is freed from the Quantum Realm, having only experienced five hours instead of years. He comes across a memorial park listing names of the vanished, including himself, then reunites with his daughter Cassie, who had been a young girl when he last saw her and is now a teenager. Lang informs the remaining Avengers and allies about his discovery: the Quantum Realm can allow time travel. While they soon determine that the nature of time travel means that they cannot simply go back in time and stop Thanos from either causing the Blip or destroying the Stones in the first place, they are able to use Pym Particles to travel through the Quantum Realm to retrieve the Infinity Stones from alternate timelines in the past.

Upon returning to the present, Tony Stark, Bruce Banner, and Rocket develop a Gauntlet composed of Stark's nanotech that is capable of harnessing the power of the Stones. Due to the powerful emission of gamma radiation resulting from the Stones' use, Banner volunteers to wear the Gauntlet and successfully restores the blipped victims in the condition they had vanished. The Avengers are then attacked by an alternate version of Thanos who intends to destroy and recreate the universe. A final battle ensues and Stark ultimately wins the battle by using the Stones to destroy Thanos and his army, at the cost of his own life. Following a funeral honoring Stark's sacrifice, Rogers travels back in time to return the Stones to their original time periods.

In Spider-Man: Far From Home, the Blip is discussed in a school news broadcast at the beginning of the film, which is the first instance in any medium of the name. The broadcast shows Midtown School of Science and Technology band members reappearing in the middle of a basketball game. The film reveals that several more characters had been blipped and restored, including Peter's aunt May Parker and his classmates Ned Leeds, MJ, Betty Brant, and Flash Thompson. Parker's teacher Roger Harrington complains that his wife had pretended to have been blipped in order to leave him. As part of a viral marketing campaign to promote the home media release of Far From Home, a real version of the fictional TheDailyBugle.net website was created that featured testimonials from supposed victims of the Blip, including one complaining that they disappeared in a dangerous situation and were seriously injured when they reappeared. This contradicted a statement by Feige saying that anyone in such a situation would have reappeared safely. Several days after this was pointed out, the website was updated to say this story was faked for an insurance claim.

### Multiverse Saga

#### Phase Four

At the beginning of the fourth episode of WandaVision, "We Interrupt This Program", Monica Rambeau is shown returning from being blipped in a hospital room, discovering chaos outside as other people are un-blipped in many places and learning that her mother Maria had died of cancer while she was gone. In the same episode, when characters outside the Westview hex first see Vision onscreen, three weeks after everyone returned, Darcy Lewis asks her colleagues to confirm that "he's dead, right? Not blipped. Dead". The writers and producers had many conversations about how to portray people returning from the Blip, and decided to set the sequence in a hospital as an interesting place to depict the scariness and confusion of the event from Monica's perspective. This is different from the portrayal of the Blip in Far From Home, which had a more comedic tone, and Schaeffer explained that Marvel was happy for the series's tone to be different as long as the visuals of the sequence matched with those seen in Far From Home.

In The Falcon and the Winter Soldier, set six months after Endgame, the Blip is referenced as having created chaos around the world. Millions of people who were displaced by the Blip came under the authority of the Global Repatriation Council, with a substantial number of people living as refugees awaiting repatriation to their home countries. Many express thankfulness to the Avengers for reversing the Blip but the event also caused violent revolutions throughout the world by organizations such as the Flag Smashers, who felt that life was better during the Blip and engage in terrorist activities to promote an anarchist society. On Sharon Carter surviving the Blip and becoming the Power Broker, series director Kari Skogland said that Carter "had to survive out there on her own during the Blip and being on the run without family — and look at what she built and where she went. She's clever, and that's what I love about it most."

The Blip is not shown to occur in the alternate universes depicted in episodes of the Disney Plus series What If...?'s first season. In the second episode, T'Challa convinces Thanos to abandon his plans of erasing half of life in the universe, while in the fifth episode Thanos arrives on Earth, having acquired five of the Infinity Stones, but is infected by the quantum virus and transformed into a zombie before he can acquire the final Stone. In the eighth episode, Thanos arrives on Earth to retrieve the Mind Stone after collecting the other Infinity Stones but is swiftly killed by Ultron, who takes the Stones for himself and sets about to annihilate all life in the multiverse.

In Shang-Chi and the Legend of the Ten Rings (2021), the Blip is discussed, and fliers can be seen in San Francisco regarding a hotline for sufferers of "post-Blip anxiety". In Eternals (2021), Ajak reveals that the Blip delayed the onslaught of the Emergence for five years, as it halved the Earth's population from the necessary level needed for it to occur. An advertisement for the Global Repatriation Council is also featured in the film.

In Hawkeye (2021), set one year after the Blip, the phrase "Thanos was right" is seen on a coffee mug and in graffiti in New York City. The event is mentioned by Kate Bishop when she deduces that Clint Barton was the Ronin. In the series it is also shown that Yelena Belova was blipped and that Maya Lopez and her father, William, survived the Blip, only for William to later die in an attack facilitated by their employer, Wilson Fisk. The series's fifth episode, "Ronin", was the first MCU media to show the Blip from the perspective of a person being blipped, with Belova seeming to almost instantly disintegrate and then reappear, with the room around her changing in appearance to signify the passage of five years.

In Spider-Man: No Way Home (2021), it is revealed that Wong replaced Stephen Strange as the Sorcerer Supreme due to Strange's disappearance during the Blip. In a mid-credits scene, a bartender explains to a universe-displaced Eddie Brock how his family was among the victims of the Blip. Although the Blip is never mentioned in Moon Knight (2022), the issue date on Marc Spector's passport is visibly shown to be December 14, 2018, which is a post-Blip date, indicating that he survived. In addition, a Global Repatriation Council banner is seen on the side of a bus in the second episode.

In Doctor Strange in the Multiverse of Madness (2022), it is revealed that Strange's former girlfriend Dr. Christine Palmer survived the Blip and, during that time, found love with another man, whom she marries at the start of the film. During the wedding, Strange also learns that his former co-worker Dr. Nicodemus West was blipped, and when he returned five years later, he was devastated to discover that his brother and cats had died during his absence. This compels West to ask Strange if there was any way that Thanos could have been defeated without the Blip occurring, prompting Strange to confirm that there was no other way.

In the first episode of She-Hulk: Attorney at Law (2022), Bruce Banner takes his cousin Jennifer Walters to his beach house/lab in Mexico that was built by Banner and Stark and explains to Walters that it's where he spent the Blip, fixing himself and merging the Hulk/Banner personas. In the second episode, Walters' mother, Elaine, reminds the family that Banner was responsible for the undoing of the Blip and that he had saved everyone with a snap of his finger. In Black Panther: Wakanda Forever (2022), it is revealed that Nakia and her son Toussaint left Wakanda immediately following the Blip, and Ramonda served as queen regnant of Wakanda during the subsequent five years.

#### Phase Five

In Ant-Man and the Wasp: Quantumania (2023), it is revealed that Hope van Dyne founded the Pym van Dyne Foundation to help the world using Pym Particles in the aftermath of the Blip, by providing reforestation and other humanitarian efforts. Cassie Lang also tried to assist with activism in helping a settlement of people who had lost their homes due to displacement following the Blip.

In Guardians of the Galaxy Vol. 3 (2023), Quill admits that he was partially responsible for the Blip happening as he recalled the events of Infinity War and how he got angry after learning about Gamora's death. In Secret Invasion (2023), Fury suffers from post-traumatic stress due to his Blip caused disintegration, leaving him more vulnerable. It is revealed that S.A.B.E.R. was made in the aftermath of Infinity War to protect Earth from other extraterrestrial threats. Fury learns that Talos, having survived the Blip, secretly brought a million refugee Skrulls to Earth while the blipped population was gone.

## Differences from the comics

In the comic books published by Marvel Comics, the event on which the initial part of the Blip is based occurred during the 1991 The Infinity Gauntlet series and came to be called the Snap. While still carried out by Thanos, it was done in an effort to impress the female personification of Death, with whom he was enamored. Thanos collects the Infinity Gems— which he uses to create the Infinity Gauntlet, making himself omnipotent—and erases half the living things in the universe to prove his love to Death. The heroes of Earth and other worlds do not become aware of these events until the Snap itself occurs, after which the surviving heroes band together against Thanos. The Snap and several related acts are quickly undone by Nebula and Adam Warlock. Warlock reveals that Thanos has always allowed himself to be defeated because the Titan secretly knows he is not worthy of ultimate power. Thanos then joins Warlock as part of the Infinity Watch and helps him to defeat various threats to the universe. As the Snap is reversed shortly after it occurs, it does not have the sort of long-term societal effects and repercussions as the Blip in the MCU. Instead the members of the Infinity Watch are each given one of the Gems, which included giving Thanos the Reality Gem. Furthermore, because the Infinity Gems are recovered from Thanos immediately and are never destroyed, they continue to play a role in later storylines in the comic books.

## Design and special effects

Weta Digital was in charge of creating the design of the dusting effect. One of the main instructions from the Russo brothers early on was that the effect had to look final, so that there was no doubt the characters were gone. The Russos also told Weta that they wanted the effect to look "painful with a component that was quite violent". They specifically didn't want it to be "too gentle or lyrical". Weta started out with a series of 2D concept frames, in which two were chosen to be combined into a full CG simulation test. The team chose to use Drax as the test character due to his lack of hair, as they wanted to get the effect design further along before dealing with hair. A highly detailed digital double was created and used as a canvas for Drax dusting. To apply the dusting effect to the other characters, complex growth algorithms were developed to apply the effect in "an organic way".

Early on in the process, Digital Design considered having "snap" briefly pop up on screen when Thanos snapped his fingers as a reference to how the snap occurred in the Infinity Gauntlet comic. Digital Domain's VFX Supervisor Kelly Port said "as a fun aside, we explored the idea of lifting the actual graphic from the frame of the comic showing the snap, the little yellow action triangles for a single frame of the moment of the snap. They appreciated the idea but didn't ultimately go for it."

Special effects supervisor Dan DeLeeuw said that many tests were done to make sure that dust scattered the correct way. The VFX team paid close attention to what each Stone did and originally incorporated all of them into the dusting effect, although DeLeeuw admits that the look was too mesmerizing, saying "we realized it had to become about less being more". The team then decided to make the Blip caused by the Power Stone specifically, as the characters' corporeal forms were left behind as they were being erased from the universe. The final version became more about depicting each character disappearing and less about the effect of the Stones.

## Reception and popular culture

The introduction of the Blip drew positive reviews from critics and audiences as an effective plot device due to its use as a plot twist in Infinity War, serious tone, and overarching implications in the MCU. Marvel Studios president Kevin Feige viewed the inclusion of the Blip as a major crux in the MCU timeline, similar to how the Battle of New York in the third act of The Avengers (2012) would go on to be referenced as a pivotal event in multiple MCU media. The depiction of the Blip at the conclusion of Avengers: Infinity War sparked various Internet meme reactions, including one referencing Peter Parker saying he does not feel good as he disintegrates, which was applied to other things.

The website, DidThanosKill.Me was created for fans to see if they would have been spared by Thanos or not, telling them either "You were spared by Thanos" or "You were slain by Thanos". The ending of Infinity War also spawned the creation of the Reddit subreddit r/thanosdidnothingwrong. A user within the subreddit suggested that half of the approximately 20,000 subscribers at the time be banned from the subreddit, in order to mimic the events of the film. After the community agreed to the measure, the moderators approached Reddit's administrators to see if the mass ban would even be possible. Once the administrators agreed to the random ban of half the subscribers, it was set to occur on July 9, 2018. Notice of the impending ban made the subreddit's subscribers increase to over 700,000, including both of the Russos who subscribed. Ahead of the ban, Brolin posted a video saying "Here we go, Reddit users," and ending it with a snap. Over 60,000 people watched a live Twitch stream of the ban occurring, which lasted several hours. The ban of over 300,000 accounts, which included Anthony Russo, was the largest in Reddit's history. Those banned then gathered in the new subreddit, /r/inthesoulstone. One Reddit user who participated described the ban as embodying "the spirit of the Internet" with people "banding together, en masse, around something relatively meaningless but somehow decidedly awesome and hilarious". Andrew Tigani of Screen Rant said this showed "how impactful the film has already become to pop culture. It is also a testament to how valuable fan interaction can be via social media".

Following the premiere of Endgame, Google included a clickable icon of the Infinity Gauntlet in Google Search results for "Thanos" or "Infinity Gauntlet" as a digital Easter egg. The icon, when clicked, made a finger-snapping motion before half of the search results disappeared, akin to the disappearance of characters following the Blip. The disappearance of the search results could also be reversed, shown by the use of the Time Stone in the Infinity Gauntlet icon.

Feige has noted the similar connotations and societal ramifications between the fictional Blip and the real-life COVID-19 pandemic, which began several months after the release of Endgame. Feige elaborated, "As we started getting into a global pandemic last March and April and May, we started to go, holy mackerel, the Blip, this universal experience...this experience that affected every human on Earth, now has a direct parallel between what people who live in the MCU had encountered, and what all of us in the real world have encountered."

In late 2020, Funko released a Funko Pop of Nick Fury in the middle of being dusted. In March 2021, to congratulate James Cameron on Avatar (2009) regaining the title as the number one film of all-time at the worldwide box office over Endgame, the Russo brothers shared an image with Thanos' armor scarecrow and the Avengers' logo dusting away into the Avatar logo.

### Scientific analysis and accuracy

The motivations held by Thanos that led to the Blip have drawn comparisons by experts to claims and works held by 18th-century scholar and economist Thomas Malthus. In 1798, Malthus theorized in An Essay on the Principle of Population, that if populations grew much faster than their food sources, and if growth remained unchecked, it would eventually lead to societal collapse. Malthus had argued that society could impose a preventative check on unrestrained growth, thereby avoiding catastrophic outcomes.

While the event wipes out half of the universe's population and not necessarily half of Earth's, modern scientific experts have commented that, in a hypothetical real-world scenario, a reduction of half of all forms of biological life on Earth would have immediate effects on biodiversity, comparable to a mass extinction event. Threatened species with preexisting low populations, as well as those species involved in pollination and food production services that require pollination management would be adversely affected. Ecosystem collapse could be possible. In relation to humans, a decrease of human overpopulation would lead to fewer emissions of greenhouse gases, which would improve the prospects of climate change mitigation and reduce global warming and its related effects. Humans would lose approximately between 1 pound (0.45 kg) and 3 pounds (1.4 kg), due to the loss of microbes and bacteria in the body. A simultaneous mass disappearance of people would also immediately trigger a substantial number of accidental and circumstantial deaths, such as airplane crashes and vehicular accidents.

## See also

- Malthusianism
- The Population Bomb, a 1968 book by Paul R. Ehrlich that inaccurately predicted worldwide famine due to overpopulation, as well as other major societal upheavals

Event in the Marvel Cinematic Universe