Can someone identify this jellyfish?

Can someone identify this jellyfish?

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Recently, I saw this video but I couldn't find out if it's CGI or if it's an actual jellyfish. If it's real, what explains its beautiful bioluminescence pattern? And could the output from the ROV thrusters rip it apart (in the video description it says so)?


Location: off the East coast of Africa.

Size: unknown, but it can be compared to the objects in the surroundings.

Additional info: footage taken in 2013.

The video you linked to, and from which you got the still shot. is real. There are hundreds of such videos now that Underwater Remotely Operated Vehicles (ROV) are more commonplace.

… could the output from the ROV thrusters rip it apart(?)

A working class ROV needed for deep ocean floor exploration can be the size of an SUV. There's no reason to believe its thrusters can't generate the shear forces needed to (sadly) tear a delicate jelly apart.

… I couldn't find out if it's CGI or if it's an actual jellyfish.

Although not a jellyfish, it is similar in being delicate; it's a ctenophore or comb jelly. The refraction/bioluminescence pattern is common in ctenophores.

And what dazzling colors these creatures display! The cilia of the ctenophores refract light in iridescent waves. Certain species are even capable of producing light, like fireflies of the sea!

For more information and videos, this short Youtube video might help. Or for a written explanation, this article, Introduction to Ctenophora ( is good.

Cnidarian Facts: Corals, Jellyfish, Sea Anemones, and Hydrozoans

The Cnidaria (Cnidaria spp.) is the phylum of animals that contains corals, jellyfish (sea jellies), sea anemones, sea pens, and hydrozoans. Cnidarian species are found throughout the world and are quite diverse, but they share many similar characteristics. When damaged, some cnidarians can regenerate their body parts, making them effectively immortal.

Fast Facts: Cnidarians

  • Scientific Name:Cnidaria
  • Common Name(s): Coelenterates, corals, jellyfish, sea anemones, sea pens, hydrozoans
  • Basic Animal Group: Invertebrate
  • Size: 3/4 of an inch to 6.5 feet in diameter up to 250 feet long
  • Weight: Up to 440 pounds
  • Lifespan: A few days to more than 4,000 years
  • Diet: Carnivore
  • Habitat: Found in all the world's oceans
  • Conservation Status: Some species are listed as threatened

Moon Jelly

The moon jelly or common jellyfish is a beautiful translucent species that has phosphorescent colors and graceful, slow movements.

Is it a Jellyfish? Yes

Identification: In this species, there is a fringe of tentacles around the bell, four oral arms near the center of the bell, and 4 petal-shaped reproductive organs (gonads) which may be orange, red, or pink. This species has a bell that grows up to 15 inches in diameter.

Where it is Found: Moon jellies are found in tropical and temperate waters, usually in temperatures of 48–66 degrees. They may be found in shallow, coastal waters and in the open ocean.

Does it Sting? A moon jelly can sting, but the sting is not as severe as some other species. It may cause a minor rash and skin irritation.


The name jellyfish, in use since 1796, [4] has traditionally been applied to medusae and all similar animals including the comb jellies (ctenophores, another phylum). [5] [6] The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either. [7] [8] In scientific literature, "jelly" and "jellyfish" have been used interchangeably. [9] [10] Many sources refer to only scyphozoans as "true jellyfish". [11]

A group of jellyfish is called a "smack". [12]



The term jellyfish broadly corresponds to medusae, [4] that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright gives the following general definition:

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle staurozoans are the exceptions [as they are stalked]. [13]

The Merriam-Webster dictionary defines jellyfish as follows:

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells. [14]

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies [15] and certain salps [15] jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa. [16] [17]

The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with ". " on the following cladogram of the animal kingdom:

Cnidaria (includes jellyfish and other jellies)

Medusozoan jellyfish

Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa. [18] [19] The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish.

Polypodiozoa and Myxozoa (parasitic cnidarians)

Narcomedusae, e.g. cosmic jellyfish [23]


The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones). [24] This suggests that the medusa form evolved after the polyps. [25] Medusozoans have tetramerous symmetry, with parts in fours or multiples of four. [24]

The four major classes of medusozoan Cnidaria are:

    are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry. Most have tentacles around the outer margin of the bowl-shaped bell, and long, oral arms around the mouth in the center of the subumbrella. [24] (box jellyfish) have a (rounded) box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to scyphozoan jellyfish than either are to the Hydrozoa. [25] medusae also have tetra-radial symmetry, nearly always have a velum (diaphragm used in swimming) attached just inside the bell margin, do not have oral arms, but a much smaller central stalk-like structure, the manubrium, with terminal mouth opening, and are distinguished by the absence of cells in the mesoglea. Hydrozoa show great diversity of lifestyle some species maintain the polyp form for their entire life and do not form medusae at all (such as Hydra, which is hence not considered a jellyfish), and a few are entirely medusal and have no polyp form. [24] (stalked jellyfish) are characterized by a medusa form that is generally sessile, oriented upside down and with a stalk emerging from the apex of the "calyx" (bell), which attaches to the substrate. At least some Staurozoa also have a polyp form that alternates with the medusoid portion of the life cycle. Until recently, Staurozoa were classified within the Scyphozoa. [24]

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 20 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not. [26] [27]

Fossil history

Since jellyfish have no hard parts, fossils are rare. The oldest conulariid scyphozoans appeared between 635 and 577 mya in the Neoproterozoic of the Lantian Formation in China others are found in the youngest Ediacaran rocks of the Tamengo Formation of Brazil, c. 505 mya, through to the Triassic. Cubozoans and hydrozoans appeared in the Cambrian of the Marjum Formation in Utah, USA, c. 540 mya. [28]

The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea, which forms the hydrostatic skeleton of the animal. [24] 95% or more of the mesogloea consists of water, [29] but it also contains collagen and other fibrous proteins, as well as wandering amoebocytes which can engulf debris and bacteria. The mesogloea is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles. [24]

On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with the mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below. [30] The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to the exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluid in a regular direction. [24]

The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium. [31] The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. [24] Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia. [24] Stalked jellyfish are attached to a solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth. [24]

Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles true jellyfish also have them around the mouth and stomach. [32] Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body some species are active swimmers most of the time, while others largely drift. [33] The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. [24] A loose network of nerves called a "nerve net" is located in the epidermis. [34] [35] Although traditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures could be considered to constitute one in most species. [36] A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction. [24]

In many species of jellyfish, the rhopalia include ocelli, light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon, where they feed, and back again. [2]

Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition, [37] supposedly making them one of the few kinds of animal to have a 360-degree view of its environment. [38]

Evolution of the Jellyfish Eye

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth. [39] Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish. [39] Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems), the eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task guided behaviors and niche specialization.

The Evolution of Jellyfish Visual Systems

Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900’s, and a rich body of research has since covered evolution of visual systems in jellyfish. [40] Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single function behaviors. More derived visual systems comprise perception that is capable of multiple task guided behaviors.

Although they lack a true brain, cnidarian jellyfish have a “ring” nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement, and culminates the emergence of photosensitive structures. [39] Across Cnidaria, there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more “conventional” eyes similar to those of vertebrates. [40] The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. [39] Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish. [39]

Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans) and other light-guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larva of hydrozoans), [40] as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking. [39] The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance. [40] [41] Light-guided behaviors are observed in numerous scyphozoans including the common moon jelly, Aurelia aurita, which migrates in response to changes in ambient light and solar position even though they lack proper eyes. [40]

The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics. [40] Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems in other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight (positive) or shadows (negative), obstacle avoidance, and control of swim-pulse rate. [42]

Box jellyfish possess “proper eyes” (similar to vertebrates) that allow them to inhabit environments that lesser derived medusae cannot. In fact, they are considered the only class in the clade Medusozoa that have behaviors necessitating spatial resolution and genuine vision. [40] However, the lens in their eyes are more functionally similar to cup-eyes exhibited in low-resolution organisms, and have very little to no focusing capability. [43] [42] The lack of the ability to focus is due to the focal length exceeding the distance to the retina, thus generating unfocused images and limiting spatial resolution. [40] The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

Box Jellyfish Eye as a Microcosm of Highly Evolved Visual Systems

Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfishes' eyes (including their task/behavior specification), and the molecular makeup of their eyes including: photoreceptors, opsins, lenses, and synapses. [40] The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary/developmental model for all visual systems. [44]

Box Jellyfish Visual Systems Overview

Box jellyfish visual systems are both diverse and complex, comprising multiple photosystems. [40] There is likely considerable variation in visual properties between species of box jellyfish given the significant inter-species morphological and physiological variation. Eyes tend to differ in size and shape, along with number of receptors (including opsins), and physiology across species of box jellyfish. [40]

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories. [45] These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes. [42] The eyes are situated on rhopalia (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish. [40] The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation. [46] The larger of the complex eyes contains a cellular cornea created by a monociliated epithelium, cellular lens, homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye. [46]

Box jellyfish have multiple photosystems that comprise different sets of eyes. [40] Evidence includes immunocytochemical and molecular data that show photopigment differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors. [40]

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo phototransduction cascades (process of light absorption by photoreceptors) that are triggered by c-opsins. [47] Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient phylogenetic opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina. [40] Nevertheless it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities. [40]

Box Jellyfish Visual Systems Comparatively

Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and crystallin composition, synapses, and Pax genes and their implied evidence for shared primordial (ancestral) genes in eye evolution. [48]

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes. [44] Research done on box jellyfish including Tripedalia cystophora has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB in situ hybridization resulted in PaxB expression in the lens, retina, and statocysts. [44] These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that it is highly likely that eyes of all organisms share a common ancestor. [44]

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance. [48] Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses. [48] This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms’ lenses exhibit. [48]

All four of the visual systems of box jellyfish species investigated with detail (Carybdea marsupialis, Chiropsalmus quadrumanus, Tamoya haplonema and Tripedalia cystophora) have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species. [45] Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas. [45]

Evolution of Box Jellyfish Eyes in Response to Environmental Stimuli

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments, as well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness. Interestingly, some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat. [49]

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish (Chironex fleckeri, Chiropsella bronzie, and Carukia barnesi). Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance, [49] and in fact, species with more complex habitats exhibit faster rates. Ch. bronzie inhabit shallow beach fronts that have low visibility and very few obstacles, thus, faster pupil contraction in response to objects in their environment is not important. Ca. barnesi and Ch. fleckeri are found in more three dimensionally complex environments like mangroves with an abundance of natural obstacles, where faster pupil contraction is more adaptive. [49] Behavioral studies support the idea that faster pupillary contraction rates assist with obstacle avoidance as well as depth adjustments in response to differing light intensities.

Light/dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment. This relates to the pupil's response to shifts between light intensity (generally from sunlight to darkness). In the process of light/dark adaptation, the upper and lower lens eyes of different box jellyfish species vary in specific function. [42] The lower lens-eyes contain pigmented photoreceptors and long pigment-cells with dark pigments that migrate on light/dark adaptation, while the upper-lens eyes play a concentrated role in light direction and phototaxis given that they face upward towards the water surface (towards the sun or moon). [42] The upper lens of Ch. bronzie does not exhibit any considerable optical power while Tr. cystophora (a box jellyfish species that tends to live in mangroves) does. The ability to use light to visually guide behavior is not of as much importance to Ch. bronzie as it is to species in more obstacle filled environments. [42] Differences in visually guided behavior serve as evidence that species that share the same number and structure of eyes can exhibit differences in how they control behavior.

Jellyfish range from about one millimeter in bell height and diameter, [50] to nearly 2 metres ( 6 + 1 ⁄ 2 ft) in bell height and diameter the tentacles and mouth parts usually extend beyond this bell dimension. [24]

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longest animal in the world, with fine, thread-like tentacles that may extend up to 36.5 m (119 ft 9 in) long (though most are nowhere near that large). [53] [54] They have a moderately painful, but rarely fatal, sting. [55] The increasingly common giant Nomura's jellyfish, Nemopilema nomurai, found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach 2 m (6 ft 7 in) in bell (body) diameter and about 200 kg (440 lb) in weight, with average specimens frequently reaching 0.9 m (2 ft 11 in) in bell diameter and about 150 kg (330 lb) in weight. [56] [57] The large bell mass of the giant Nomura's jellyfish [58] can dwarf a diver and is nearly always much greater than the Lion's Mane, whose bell diameter can reach 1 m (3 ft 3 in). [59]

Life cycle

Jellyfish have a complex life cycle which includes both sexual and asexual phases, with the medusa being the sexual stage in most instances. Sperm fertilize eggs, which develop into larval planulae, become polyps, bud into ephyrae and then transform into adult medusae. In some species certain stages may be skipped. [61]

Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day in many instances this is at dawn or dusk. [62] Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the unprotected eggs are fertilized and develop into larvae. In a few species, the sperm swim into the female's mouth, fertilizing the eggs within her body, where they remain during early development stages. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae. [63]

The planula is a small larva covered with cilia. When sufficiently developed, it settles onto a firm surface and develops into a polyp. The polyp generally consists of a small stalk topped by a mouth that is ringed by upward-facing tentacles. The polyps resemble those of closely related anthozoans, such as sea anemones and corals. The jellyfish polyp may be sessile, living on the bottom, boat hulls or other substrates, or it may be free-floating or attached to tiny bits of free-living plankton [64] or rarely, fish [65] [66] or other invertebrates. Polyps may be solitary or colonial. [67] Most polyps are only millimetres in diameter and feed continuously. The polyp stage may last for years. [24]

After an interval and stimulated by seasonal or hormonal changes, the polyp may begin reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. Budding produces more scyphistomae and also ephyrae. [24] Budding sites vary by species from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. [64] In a process known as strobilation, the polyp's tentacles are reabsorbed and the body starts to narrow, forming transverse constrictions, in several places near the upper extremity of the polyp. These deepen as the constriction sites migrate down the body, and separate segments known as ephyra detach. These are free-swimming precursors of the adult medusa stage, which is the life stage that is typically identified as a jellyfish. [24] [68] The ephyrae, usually only a millimeter or two across initially, swim away from the polyp and grow. Limnomedusae polyps can asexually produce a creeping frustule larval form, which crawls away before developing into another polyp. [24] A few species can produce new medusae by budding directly from the medusan stage. Some hydromedusae reproduce by fission. [64]


Little is known of the life histories of many jellyfish as the places on the seabed where the benthic forms of those species live have not been found. However, an asexually reproducing strobila form can sometimes live for several years, producing new medusae (ephyra larvae) each year. [69]

An unusual species, Turritopsis dohrnii, formerly classified as Turritopsis nutricula, [70] might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage, thereby escaping the death that typically awaits medusae post-reproduction if they have not otherwise been eaten by some other organism. So far this reversal has been observed only in the laboratory. [71]


Using the moon jelly Aurelia aurita as an example, jellyfish have been shown to be the most energy efficient swimmers of all animals. [72] They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two vortex rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming. [73] [74] [75]

Jellyfish are like other cnidarians generally carnivorous (or parasitic), [76] feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely the tentacles, which contain nematocysts to stun or kill the prey, may then flex to help bring it to the mouth. [24] Their swimming technique also helps them to capture prey when their bell expands it sucks in water which brings more potential prey within reach of the tentacles. [77]

A few species such as Aglaura hemistoma are omnivorous, feeding on microplankton which is a mixture of zooplankton and phytoplankton (microscopic plants) such as dinoflagellates. [78] Others harbour mutualistic algae (Zooxanthellae) in their tissues [24] the spotted jellyfish (Mastigias papua) is typical of these, deriving part of its nutrition from the products of photosynthesis, and part from captured zooplankton. [79] [80]


Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include tunas, sharks, swordfish, sea turtles and penguins. [81] [82] Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds. [83] In general however, few animals prey on jellyfish they can broadly be considered to be top predators in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering. [84]


Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap they are safe from potential predators and are able to share the fish caught by the jellyfish. [85] The cannonball jellyfish has a symbiotic relationship with ten different species of fish, and with the longnose spider crab, which lives inside the bell, sharing the jellyfish's food and nibbling its tissues. [86]


Jellyfish form large masses or blooms in certain environmental conditions of ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect marine currents and swim against the current to congregate in blooms. [88] [89] Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters. [90] Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing eutrophication and algal blooms. When the phytoplankton die, they may create dead zones, so called because they are ahypoxic (low in oxygen). This in turn kills fish and other animals, but not jellyfish, [91] allowing them to bloom. [92] [93] Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators. [94] [95] Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly they prey upon many species, while few species prey on them and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters. [96] [97] It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs and larvae. [98] [99] [100] [93]

Some jellyfish populations that have shown clear increases in the past few decades are invasive species, newly arrived from other habitats: examples include the Black Sea, Caspian Sea, Baltic Sea, central and eastern Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic (including the Caribbean, Gulf of Mexico and Brazil). [103] [104]

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers. [105] Reductions in zooplankton and icthyplankton due to a jellyfish bloom can ripple through the trophic levels. High density jellyfish populations can out compete other predators and reduce fish recruitment. [106] Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels. [107]

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms. [108] Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton. [108] Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition. [109] [110] The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

These blooms have very real impacts on industries. Jellyfish can out compete fish by utilizing open niches in over-fished fisheries. [111] Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water. [112] Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches. [113]

Jellyfish form a component of jelly-falls, events where gelatinous zooplankton fall to the seafloor, providing food for the benthic organisms there. [114] In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom. [115]


Most jellyfish are marine animals, although a few hydromedusae inhabit freshwater. The best known freshwater example is the cosmopolitan hydrozoan jellyfish, Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting. [116] Some jellyfish populations have become restricted to coastal saltwater lakes, such as Jellyfish Lake in Palau. [117] Jellyfish Lake is a marine lake where millions of golden jellyfish (Mastigias spp.) migrate horizontally across the lake daily. [80]

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus Cassiopea typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom. [118]

Some species explicitly adapt to tidal flux. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt. [2]


Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish. [119] [120]


Jellyfish have long been eaten in some parts of the world. [3] Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus meleagris, along the southern Atlantic coast of the United States and in the Gulf of Mexico for export to Asia. [122]

Jellyfish are also harvested for their collagen, which is being investigated for use in a variety of applications including the treatment of rheumatoid arthritis. [123]


Aristotle stated in the Parts of Animals IV, 6 that jellyfish (sea-nettles) were eaten in winter time in a fish stew. [124]

In some countries, including China, Japan, and Korea, jellyfish are a delicacy. The jellyfish is dried to prevent spoiling. Only some 12 species of scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food, mostly in southeast Asia. [125] Rhizostomes, especially Rhopilema esculentum in China ( 海蜇 hǎizhé, 'sea stingers') and Stomolophus meleagris (cannonball jellyfish) in the United States, are favored because of their larger and more rigid bodies and because their toxins are harmless to humans. [122]

Traditional processing methods, carried out by a jellyfish master, involve a 20- to 40-day multi-phase procedure in which, after removing the gonads and mucous membranes, the umbrella and oral arms are treated with a mixture of table salt and alum, and compressed. Processing makes the jellyfish drier and more acidic, producing a crisp texture. Jellyfish prepared this way retain 7–10% of their original weight, and the processed product consists of approximately 94% water and 6% protein. Freshly processed jellyfish has a white, creamy color and turns yellow or brown during prolonged storage. [122]

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish is often served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer. [122] [126] Desalted, ready-to-eat products are also available. [122]


Pliny the Elder reported in his Natural History that the slime of the jellyfish "Pulmo marinus" produced light when rubbed on a walking stick. [127]

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and another bioluminescent protein, called aequorin, from the large and abundant hydromedusa Aequorea victoria, while studying photoproteins that cause bioluminescence in this species. [128] Three decades later, Douglas Prasher sequenced and cloned the gene for GFP. [129] Martin Chalfie figured out how to use GFP as a fluorescent marker of genes inserted into other cells or organisms. [130] Roger Tsien later chemically manipulated GFP to produce other fluorescent colors to use as markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for their work with GFP. [128] Man-made GFP became widely used as a fluorescent tag to show which cells or tissues express specific genes. The genetic engineering technique fuses the gene of interest to the GFP gene. The fused DNA is then put into a cell, to generate either a cell line or (via IVF techniques) an entire animal bearing the gene. In the cell or animal, the artificial gene turns on in the same tissues and the same time as the normal gene, making GFP instead of the normal protein. Illuminating the animal or cell reveals what tissues express that protein—or at what stage of development. The fluorescence shows where the gene is expressed. [131]

Aquarium display

Jellyfish are displayed in many public aquariums. Often the tank's background is blue and the animals are illuminated by side light, increasing the contrast between the animal and the background. In natural conditions, many jellies are so transparent that they are nearly invisible. [132] Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place. Professional exhibits as in the Monterey Bay Aquarium feature precise water flows, typically in circular tanks to avoid trapping specimens in corners. They have a live "Jelly Cam". [133] The outflow is spread out over a large surface area and the inflow enters as a sheet of water in front of the outflow, so the jellyfish do not get sucked into it. [134] As of 2009, jellyfish were becoming popular in home aquariums, where they require similar equipment. [135]


Jellyfish are armed with nematocysts. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, [136] but only some species' venom causes an adverse reaction in humans. [137] In a study published in Communications Biology, researchers found a jellyfish species called Cassiopea xamachana which when triggered will release tiny balls of cells that swim around the jellyfish stinging everything in their path. Researchers described these as "self-propelling microscopic grenades" and named them cassiosomes. [138]

The effects of stings range from mild discomfort to extreme pain and death. [139] [140] Most jellyfish stings are not deadly, but stings of some box jellyfish (Irukandji jellyfish), such as the sea wasp, can be deadly. Stings may cause anaphylaxis (a form of shock), which can be fatal. Jellyfish kill 20 to 40 people a year in the Philippines alone. In 2006 the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava. [140] [141]

Vinegar (3–10% aqueous acetic acid) may help with box jellyfish stings [142] [143] but not the stings of the Portuguese man o' war. [142] Salt water may help if vinegar is unavailable. [142] [144] Rubbing wounds, or using alcohol, ammonia, fresh water, or urine is not advised, as they can encourage the release of more venom. [145] Clearing the area of jelly and tentacles reduces nematocyst firing. [145] Scraping the affected skin, such as with the edge of a credit card, may remove remaining nematocysts. [146] Once the skin has been cleaned of nematocysts, hydrocortisone cream applied locally reduces pain and inflammation. [147] Antihistamines may help to control itching. [146] Immunobased antivenins are used for serious box jellyfish stings. [148] [149]

Mechanical issues

Jellyfish in large quantities can fill and split fishing nets and crush captured fish. [150] They can clog cooling equipment, disabling power stations in several countries jellyfish caused a cascading blackout in the Philippines in 1999, [140] as well as damaging the Diablo Canyon Power Plant in California in 2008. [151] They can also stop desalination plants and ships' engines. [150] [152]

10 Different Types of Jellyfish

Many people think of jellyfish as some of the smallest animals found in the ocean, but they really do come in all different sizes. Currently, around 2000 jellyfish types have been documented, but scientists estimate that there could still be over 300,000 species yet to be discovered. That’s a lot of jellies…

Here we have put together, in no particular order, ten alien yet beautiful looking marine animals that will raise your eyebrows and make you think twice about what’s really out there in the big blue. If you love jellyfish so much then you have to check out these jellyfish gift ideas!

1. Crystal Jellyfish

Coming in at number one is the Crystal jellyfish. Located in the waters around North America’s coast, this jellyfish species is actually completely colorless, hence its name! This beautiful specimen has around 150 tentacles lining its glass-like bell and in the daylight looks crystal clear. Although, this transparency belies a brighter side.

The Monterey Bay Aquarium says that “Crystal jellies are brightly luminescent jellies, with glowing points around the margin of the umbrella.

The components required for bioluminescence include a Calcium++ activated photoprotein, called aequorin that emits a blue-green light, and an accessory green fluorescent protein (GFP), which accepts energy from aequorin and re-emits it as a green light.

Scientists have created ‘green mice’ that glow green when hit by blue light by inserting the GFP gene from the crystal jelly into the mice. The glowing protein is a widely used biological highlighter that helps scientists find and study genes more quickly.”

2. Bloodybelly Comb Jellyfish

Ranking high in the charts for the coolest and beautiful jelly-fish, is our next contender, the Bloodybelly Comb jellies, which, technically speaking are comb jellies and are only very distantly related to the jellyfish. This one doesn’t have the famous jellyfish stinging tentacles that others possess, and it is actually a harmless Comb jelly to humans.

However, what they lack in tentacles they certainly make up for in their cilia, cilia are tiny hair-like projections that beat back and forth to help propel it through the water. This movement of the cilia creates a beautiful sparkling light show showing an array of colors.

Despite a reputation of potentially being a “showoff”, the red color that the Bloodybelly Comb jellies turn actually makes it nearly invisible when in deep water, which is where they are normally found.

Red looks very much like black in the depths of the ocean and specifically, the red belly of this Bloodybelly comb also helps to mask the bioluminescence glow of its prey and keeps it extra safe from the attention of its predators.

3. Cauliflower Jellyfish

Getting its name from the wart-like projections this type has on its bell resembling that of a vegetable, we give you the Cauliflower jellyfish also referred to as the Crown jellyfish! While this jelly may not sound the prettiest of its species, it is still a truly beautiful species of jellyfish.

Most commonly found within the waters of the mid-Pacific to the Indo-Pacific and sometimes also around the Atlantic Ocean off of the West African coast. The Cauliflower jelly grows relatively large in size reaching up to 1.5 to 1.9 feet in diameter.

Although it is one of the most venomous of the jellyfish species they are actually harmless to humans. What do jellyfish eat? just plankton, algae, shrimp, and invertebrate eggs. Although they have 30 filaments with stinging cells sticking out from their bell, they are harmless to humans, so no painful stings from these little marine animals.

Very much like its vegetable nickname, this kind is often also found on dinner plates! Mostly in China and Japan where the species is considered to be a delicacy and is also known to be used for medicinal purposes within these locations.

4. White-spotted Jellyfish

At number four on, we have the White-spotted jellyfish. These jellies have very mild venom and therefore any jellyfish stings from its stinging cells are harmless to us humans. In fact, the white-spotted jelly doesn’t generally even use their venom to catch food at all!

What do the jellyfish eat? Well, these are what’s known as a filter feeder, similar to oysters and sponges. They can filter over 50 cubic meters of ocean water every single day! The only downside of this type of jellyfish is that a swarm (or bloom) of these jellies can clear an area of zooplankton! Greedy little things!

Causing a shortage for the fish and crustaceans that also munch on the microscopic marine life. In such areas where the white-spotted jelly is considered to be an invasive species, such as the Gulf of California, the Caribbean Sea and the Gulf of Mexico, their hungry appetite poses somewhat of a problem for the native species from shrimps to corals.

5. Black Sea Nettle Jellyfish

Next, one of the largest jellyfish (the largest jellyfish is the Lion Mane jellyfish) is the Black Sea Nettles jellyfish! This particular species can be found in the deep sea Pacific waters around Southern California.

The bell of the Black Sea Nettles can reach up to three-foot across, its long tentacles reach up to 20 feet in length, and its stinging tentacles 25 feet long. Without saying, it would be pretty damn scary if you caught yourself in the middle of a bloom of these giants while in the water, but don’t worry too much as they are not that common to a lot of ocean waters.

Although it is called a Black Sea Nettle, the bell is only black on the mature jellies, with the bell of immature and small mature jellies being a reddish to maroon color, while the tentacles are whitish-pink and oral arms a reddish-pink in both the large and small black sea nettle.

Considering their size, which is large, this is one of the jellyfish species that are relatively new to science and we don’t actually know that much about them. It has been said that this is partly due to them being very difficult to raise in captivity and they aren’t very often discovered in the wild.

There has, however, previous encounters where the largest blooms of Black Sea Nettles have surfaced in 1989, 1999, and in 2010. But other than these occurrences, what the largest of the jellies tend to get up to it a little bit of a mystery.

6. Fried Egg Jellyfish

At sixth on our celebratory list, is the Fried Egg Jelly. Now, I wonder why they call this the Fried Egg, any ideas. Another of the jellies that have venom but does not usually affect humans, in fact, its sting is so mild that the tentacles are sometimes used to by small fish to provide shelter in the open ocean water.

This is the Cotylorhiza tuberculata, better known as the Fried Egg jellyfish or even the Mediterranean jelly. This particular species actually only survive for around 6 months, from the summer months until the winter, dying when the weather and water start to cool down.

If you spot them while diving, take a close look and you will be able to find the tiny fish that hide inside the tentacles for their own protection, sometimes, a smaller crab species will also take a chance and hitch a ride on the bell too!

This egg colored jellyfish can be found lazing in the Atlantic Ocean, Mediterranean Sea, and the Aegean Sea.

7. Flower Hat Jellyfish

No this isn’t a species that wears a floral hat! Sorry to disappoint you! But you can see where the Flower Hat jellyfish gets its common name from. Seventh, on our list, these sea jellies are endemic to the Western Pacific, commonly found off the Southern Japan coast and also within the waters of Brazil and Argentina.

They tend to mostly hang about near the ocean floor among the seagrass rather than pulsing their way through the open ocean. For these stinging jellyfish, the seagrass is better for them in order to catch the small fish which they prey on.

Although alien-like, this is a beautiful jellyfish, but don’t be fooled by the extraordinary colors of it bell that it possesses, you will know about it if it stings you as it is painful! According to the Monterey Bay Aquarium “Blooms of the flower hat jellies make swimming in coastal waters off Argentina hazardous”.

The sting of this jelly is painful, leaving a bright burn like a rash. In Brazil, swarms of the Flower Hat sea jellies interfere with shrimp fishing, as they clog their nets and drive shrimp away, probably to deeper water.

8. Atolla Jellyfish

Coming in at number eight on our list it the Atolla jellyfish. Also known as the Coronate Medusa jelly, this can be found all around the world. Like, most deep sea-dwelling creatures the Atolla has super awesome bioluminescent abilities.

Most deep-sea ocean dwellers use their bioluminescence to attract prey, but this type actually uses it to keep it from becoming prey! Once attacked, the Atolla creates a series of flashes, similar to that of an emergency siren. It’s the flashes that this species produces that draws in more predators.

The idea is that the predators will be more interested in the original attacker, rather than the Atolla, allowing the jelly a chance to make a getaway!It is this strategy that has given the Atolla the nickname “alarm jellyfish” deep-sea species.

9. Narcomedusae Jellyfish

Known to have a Darth Vader kind of appearance, we give you our next jelly, the Narcomedusae. Out of the different species of jellyfish, this rather unusual type has strangely, not one, but two stomach pouches. To be able to fill both pouches with prey, the Narcomedusae holds its long tentacles out in front of it when swimming.

Researchers believe that this is to make them a more effective ambush predator. According to the unexpected world of biology, the people at Creature Cast have said that Some species of Narcomedusae (affectionately called narcos by the people that study them) can grow inside their own mother, rather than laying the usual jellyfish eggs, and this provides nourishment and a safe environment for her young.

The narco babies can then leave their mother, find another jelly of an entirely different species, attach to its flesh, and thrive on the nourishment and safe environment it provides.”

10. Pink Meanie Jellyfish

Last but not least on our celebratory list of all types of jellyfish is another of the largest jellyfish and is the Pink Meanie jellyfish! Having only been first observed in large groups in the year 2000 off of the Gulf of Mexico, it is a mystery as to how one of these pink jellyfish of this large size hadn’t been discovered sooner.

So the pink meanie and its Mediterranean cousin represent a new family of jellyfish altogether, the first new family of jellies species identified since 1921.

The Pink Meanie has a taste for other jellies and actually preys on them! Using its very long, up to a 70 feet reach, tentacles to entangle them, they then reel in their victims and consume them. These creatures have been known to eat as many as 34 at a time! It sounds like something out of a horror movie, doesn’t it!!

We know that this species inhabits the US Atlantic, the Coastal Caribbean, and the Gulf of Mexico, but also perhaps other parts of the world too. The Pink Meanie is also known to be named Drymonema Larsoni after the U.S. Fish and Wildlife scientist Ronald Larson, the man that pioneered work on this species back in the early ’80s. Read more about it here.

Psstttt… Do you know someone that would love a Jellyfish themed gift? Or just want to show off your love for these weird and beautiful jellyfish, sea animals? You can do so with one of these awesome themed products

Some Jellyfish Are 98 Percent Water

The main body of a jellyfish—its bell—is made of two thin layers of cells with non-living, watery material in between, says jellyfish biologist Lucas Brotz, a postdoctoral research fellow at the University of British Columbia in Vancouver.

This simple structure is a “neat evolutionary trick,” he says, that lets them grow big and eat more things without the cost of a high metabolism.

“They’ve survived every mass extinction,” Brotz says. While most species that ever lived have gone extinct, “this group of bags of water that have somehow survived,” for over 600 million years.

Your Top 10 Jellyfish Questions Answered

Jellyfish are among the most fascinating (and unique-looking) creatures of the sea! Did you know that these ancient invertebrates have been around long before dinosaurs roamed the Earth — more than 500 million years ago ? Even though jellyfish have one of the most basic nervous system in a multicellular organism, they are able to produce toxic venom, emit light and may even hold the secrets to immortality (perhaps Voldemort should have looked into this?).

But there are many misconceptions surrounding jellyfish, finding that even my own basic knowledge comes only from a completely healthy dose of Spongebob episodes (did anyone else notice that they’re pretty much underwater bees?). But alas, Spongebob is an unreliable source to turn to for jellyfish information. So, in my pursuit for non-animated, accurate jellyfish facts, I’ve compiled a tidy list of all those questions that have kept you up at night.

Are jellyfish fish?

© Monterey Bay Aquarium NOPE! Jellyfish are an animal in the Phylum Cnidaria and the Subphylum Medusozoa. While they are popularly called “jellyfish,” many marine biologists prefer the terms “jelly” or “sea jelly” to avoid confusion. But given that it is World Jellyfish Day, I’ll be sticking with the traditional usage.

Are jellyfish poisonous to humans?

© Photosbykerry All jellyfish produce toxins with varying levels of “stings.” Only about 2% of jellyfish toxins are seriously harmful to humans.

What is the deadliest jellyfish in the world?

© Monterey Bay Aquarium One of the deadliest jellyfish in the world is the Box Jellyfish. Found primarily off the coast of northern Australia and in the Indo-Pacific, the Box Jellyfish can have 24 eyes and 15 tentacles that can reach up to three meters (10 feet) in length. Other jellyfish with powerful venom include the Irukandji, Portuguese Man o’ War, Lion’s Mane, and Sea Nettle jellyfish.

How can a jellyfish kill you?

There are about 50 species of jellyfish that have tentacles covered in cnidocytes (basically a cell that explodes when touched). Each cnidocyt contains a tiny dart with poison that, once it pierces the skin, enters the blood causing a dangerous spike in blood pressure that can stop the heart. The U.S. National Science Foundation reports that around 20 to 40 people die each year from box jellyfish stings in the Philippines. Worldwide fatalities from jellyfish are unknown due to some countries’ lack of a death certificate requirement.

Can a jellyfish live forever?

© Shutterstock The life span of jellyfish varies among species, with some only living a few days, others to a year, and a few up to 20 years. There is one species of jellyfish, the Turritopsis dohrnii, that has been dubbed ‘immortal.’ This jellyfish can reprogram the identity of its cells, essentially rewinding its life cycle. When the jellyfish is old, sick, or facing danger, its survival mechanism allows it to become a younger version of itself.

Is it okay to pee on a jellyfish sting?

© Gary Kavanagh No matter what you’ve seen on Friends, do not urinate on a jellyfish sting! Jellyfish stings should NOT be cleaned with freshwater (which urine contains) as it will not alleviate any burn and may in fact cause increased pain. As soon as you get stung, leave the water and carefully remove any remaining tentacles without making additional skin contact. To alleviate a burn, try vinegar or a baking soda paste, and if you continue to feel ill, please see a doctor.

What good do jellyfish do?

© Alexander Semenov Jellyfish are crucial to ocean health. They keep prey like zooplankton and small fish populations in check by paralyzing them with their tentacles and gobbling them up. Jellyfish also transport carbon to greater ocean depths, enhancing biodiversity and contributing to medical advances.

Can jellyfish feel pain?

© Kevin Raskoff Jellyfish don’t feel pain in the same way that humans would. They do not possess a brain, heart, bones, nor a respiratory system. They are 95% water and contain only a basic network of neurons that allow them to sense their environment.

Can jellyfish glow in the dark?

© Ocean River Some jellyfish have bioluminescent organs which enable them to emit light. This is believed to be primarily used as a defense mechanism to distract predators, but can be used to attract prey or for intraspecific communication

Are jellyfish aliens?

© NOAA No, no they are not (though they can look like flying saucers in a dimly lit ocean).

While there are plenty more questions that we can ask about jellyfish, there is still much information about how these organisms operate that is unknown. It is our hope that this will at least bring you a small step closer towards understanding the countless jellyfish that roam the sea.

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Box Jellyfish Reproduction

Box Jellyfish have the ability to reproduce both sexually and asexually. They are either male or female based on their DNA profile. However, they have the ability to offer both eggs and sperm independently. Once the eggs have been offered then sperm mixes with them to create larvae.

This stage can take a long time, even more than a year. The polyps will continue to grow and to branch out. There can be hundreds of them connected through very thin feeding tubes. As food supplies come along then the nutrients are distributed to all of the polyps through those feeding tubes.

Over time the polyps will start to breach off from each other. This is when there will be the actual Box Jelly fish. Before it can breach off though a mouth has to form, eyes form, and more tentacles form so that it will be able to swim away and care for itself. The average life span in the wild is less than 1 year.

Can someone identify this jellyfish? - Biology

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JELLY PACK: A bloom of moon jellyfish, which get their name from their circular shape

CCSS: Reading Informational Text: 2

Are people to blame for a growing number of jellyfish swarming the seas?

ESSENTIAL QUESTION: What factors might cause a population of organisms to suddenly increase?

What should have been a fun trip to the beach last June soon turned into a nightmare for thousands of visitors to Florida’s eastern coast. Over the course of two weeks, more than 3,000 beachgoers were stung by nettle and moon jellyfish. Luckily, no one was seriously injured. Although stings from these types of jellies can be extremely painful, they’re rarely deadly.

Last June, visitors flocked to Florida’s eastern coast. It should have been a fun trip to the beach. But it soon turned into a nightmare for thousands of people. More than 3,000 visitors were stung by nettle and moon jellyfish over a two-week period. Luckily, no one was seriously hurt. Stings from these types of jellies can be extremely painful, but they’re rarely deadly.

This map shows areas with increased sightings of jellyfish blooms, represented by red triangles and blue squares. Scientists are uncertain whether more blooms are in fact occurring or if people are just better at reporting them than in the past.

This map shows areas with increased sightings of jellyfish blooms, represented by red triangles and blue squares. Scientists are uncertain whether more blooms are in fact occurring or if people are just better at reporting them than in the past.


This map shows areas with increased sightings of jellyfish blooms, represented by red triangles and blue squares. Scientists are uncertain whether more blooms are in fact occurring or if people are just better at reporting them than in the past.

This map shows areas with increased sightings of jellyfish blooms, represented by red triangles and blue squares. Scientists are uncertain whether more blooms are in fact occurring or if people are just better at reporting them than in the past.


This is just one recent encounter between people and swarms of jellyfish, called blooms , in the worlds’ oceans. Reports of these incidents have been on the rise for the past few decades ( see Jellyfish Sightings ). Jellyfish blooms can cover thousands of square miles and cause all sorts of trouble. In places like Israel, Japan, the Philippines, Scotland, Sweden, and the U.S., the gelatinous animals have clogged intake pipes at power plants that pull in water from the ocean to cool machinery. That can cause the plants to temporarily shut down. Large masses of jellies also frustrate people who are fishing by damaging their nets and gumming up boat engines.

“There are definitely more reports of jellyfish blooms from more locations,” says Mark Q. Martindale, a marine biologist at the University of Florida. He explains that scientists are unsure whether blooms are really increasing or if reporting of the occurrences has just improved. However, Martindale says changing climate patterns and human activities, like overfishing, could be affecting jellyfish numbers. That could result in larger blooms showing up more often closer to shores—and in places where they haven’t been spotted before.

This is just one recent run-in between people and swarms of jellyfish in the worlds’ oceans. Reports of these events have been increasing for the past few decades (see Jellyfish Sightings). Swarms of jellyfish are called blooms. They can cover thousands of square miles and cause all sorts of trouble. Some power plants pull ocean water in through pipes to cool machinery. Jellyfish have clogged these pipes in places like Israel, Japan, the Philippines, Scotland, Sweden, and the U.S. That can cause the plants to shut down for a while. Large masses of jellies also make trouble for fishermen. The jellies damage fishing nets and gum up boat engines.

“There are definitely more reports of jellyfish blooms from more locations,” says Mark Q. Martindale. He’s a marine biologist at the University of Florida. He explains that scientists aren’t sure why. Are blooms really increasing, or are they just being reported better? But Martindale says changing climate patterns could be affecting jellyfish numbers. So could human activities, like overfishing. That could result in larger blooms showing up more often, closer to shores, and in completely new places.

Jellyfish almost killed this scientist. Now, she wants to save others from their fatal venom

TALAO-TALAO, THE PHILIPPINES—On 17 June, several families were celebrating Father's Day here at Dalahican Beach, a popular bathing spot near Lucena, a city on Luzon island. A steady breeze blew across sand that looked like fine brown sugar. Children splashed in the dark green water. Suddenly, people started to scream as a toddler was lifted unconscious from the water, his lips pale. A witness recalled that dark lashes crawled across the toddler's thighs—the telltale marks of a jellyfish sting. The boy's family simply held him and cried. Shortly after, Prince Gabriel Mabborang, 18 months old, was dead—one of at least three children killed in the Philippines this summer by the stings of box jellyfish.

On a midmorning 3 weeks later, Angel Yanagihara, who studies jellyfish venom at the University of Hawaii (UH) in Honolulu, arrived at Dalahican Beach. After slipping into a full-body wetsuit, she slung a box over her shoulder, put on gloves, and walked into the sea. No reminders of the recent tragedy were present children were playing in the shallows, clapping their hands to Filipino songs. "Hello! What's your name?" they giggled as Yanagihara, 58, walked by. Yanagihara spent almost 3 hours wading in waist-deep waters, hoping to catch box jellyfish for her studies of their venom. One of the nearly transparent animals swam to the surface, almost within reach, but then escaped as she approached. She emerged empty-handed, but villagers had brought her two specimens earlier that day.

Among the world's public health problems, jellyfish stings may seem trivial, affecting millions of people each year but known to kill only a few dozen. But many deaths may go unrecorded, and in some places, jellyfish stings take a real toll. Prince Gabriel was the second child killed on the same beach in the past year, and many people in the area bear the scars of nonfatal attacks. After news of the boy's death spread rapidly on social media, Lucena health officials invited Yanagihara to talk about jellyfish venom and how to save sting victims, a service she provided for free. She spoke at a basketball court by the beach, and as she flipped to her slide on first aid, cellphones rose in a wave, snapping photos.

Her message was clear—and controversial. Yanagihara has staked out one corner in a debate over how the venom of box jellyfish kills, stopping the heart in as little as 5 minutes. What she calls her unified field theory holds that the venom contains proteins that puncture red blood cells and release potassium, disrupting the electrical rhythms that keep the heart beating. Her conclusions, and the treatments she has based on them, emerged from 20 years of science that colleagues praise as thorough and imaginative. Yanagihara "has done a great favor to the field in doing systematic comparisons" of methods to collect and study the venom, says Kenneth Winkel, a former director of The University of Melbourne's Australian Venom Research Unit who is now at the university's Melbourne School of Population and Global Health.

But nobody has independently replicated Yanagihara's methods and findings or tested her treatments. Some jellyfish researchers say other compounds in the venom are the real killers and that different remedies—or none at all—are more likely to work. "Jellyfish venom is a graveyard for simplistic causation and therapy," Winkel says.

Research that would resolve the debates is scarce. Worldwide, only about five research groups study jellyfish venom. Funders prefer to focus on bigger public health problems—although Yanagihara thinks the stings exact a much higher death toll than most people assume. So she and her few colleagues and competitors struggle on with small budgets to study the threat, develop remedies, and educate communities at risk.

Most of the 4000 species of jellyfish cause only pain and discomfort when they sting humans. Only Cubozoans, or box jellyfish, of which some 50 species inhabit tropical and temperate seas around the globe, are fatal. They take their name from their cubic body, which has between four and 15 tentacles up to 3 meters long growing from each of the four corners. The tentacles are carpeted with hundreds of thousands of specialized cells, each harboring a capsule called a nematocyst that can fire a microscopic harpoon at speeds of more than 60 kilometers per hour. The harpoon carries a spiny hollow tube that injects venom after it strikes a victim.

Yanagihara, born in Alaska, hadn't planned to study jellyfish. But in 1997, the year she obtained her Ph.D. at UH for research on cellular ion channels, the jellyfish found her. One day that year, Yanagihara swam out to sea before dawn—"My father taught me to swim before I walked," she says—when she encountered a swarm of box jellyfish some 500 meters offshore. She felt needles burning into her neck and arms and her lungs collapsing her arms began to fail. She switched to a breathing technique she had learned for childbirth and clawed back to shore in agony, "like an automaton." The pain kept her in bed for 3 days. After she recovered, she wanted to know what almost killed her.

In some cases, box jellyfish venom causes Irukandji syndrome, in which an overload of stress hormones and inflammation proteins produces pain and nausea for days, as well as high blood pressure that can lead to brain hemorrhage and death. Most sting casualties, however, die within minutes from cardiac arrest. The prevailing hypothesis 20 years ago was that the culprits are ion channel blockers, molecules that disrupt movement of ions in and out of cells. The blockage shuts down nerve and muscle cells, including those that keep the heart pumping.

To test the idea, Yanagihara followed a standard procedure for studying jellyfish venom: She dissolved the tentacles in water to release the nematocysts and broke them with a mortar and pestle or glass beads to release the venom. Then she exposed immature frog egg cells—a common model in cell physiology—to the venom and measured ion movement using electrophysiological techniques. But the experiments kept failing. After scrutinizing every part of her experimental setup, she began to wonder whether her venom preparation was too impure to reveal its secrets. She realized that crushing the nematocysts produced a crude mix of venom and cellular debris—akin to putting "a rattlesnake in a blender" to get its venom, she says.

Taking a cue from a 1970s study, she developed a new method that uses citrate, an acidic compound, to dislodge the nematocysts without breaking them. She then puts them in a French press, in which a piston forcibly ruptures all the nematocysts at once. A minuscule harvest of venom squeezes out through a tiny outlet that filters larger cellular components.

The yield is excruciatingly low: some 10 milliliters of venom from 1000 box jellyfish. (Yanagihara collects a species named Alatina alata, often called the sea wasp, en masse in Hawaii.) But the result, she says, is a much purer venom. In it she found not only ion channel blockers, but also many porins, proteins that puncture cells, allowing their contents to leak out. She suspected hemolysis—the destruction of red blood cells by porins—might be the fatal mechanism.

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