Jellyfish

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This article is about the aquatic animal-form. For similar animals, see gelatinous zooplankton. For other uses, see Jellyfish (disambiguation).
Jellyfish
Temporal range: 505–0Ma
Cambrian – Recent
Pacific sea nettle
Chrysaora fuscescens
Scientific classification e
Kingdom: Animalia
Phylum: Cnidaria
Subphylum: Medusozoa
Petersen, 1979
Classes
Flower hat jelly, Olindias formosa, photographed at Osaka Aquarium

Jellyfish are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.

Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years,[1] and possibly 700 million years or more, making them the oldest multi-organ animal.[2]

Contents

Terminology

The term medusa was coined by Linnaeus in 1752, alluding to the tentacled head of Medusa in Greek mythology.[3] This term refers exclusively to the non-polyp life-stage which occurs in many cnidarians, which is typified by a large pulsating gelatinous bell with long trailing tentacles. All medusa-producing species belong to the sub-phylum Medusozoa.

The English popular name jellyfish has been in use since 1796.[3] It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores (members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) were included as "jellyfishes".[4] Even some scientists include the phylum ctenophora when they are referring to jellyfish.[5] Other scientists prefer to use the more all-encompassing term gelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column.[6]

As jellyfish are not even vertebrates, let alone true fish, the usual word jellyfish is considered by some to be a misnomer, and American public aquariums have popularized use of the terms jellies or sea jellies instead.[7]

Many textbooks and websites refer to only scyphozoans as "true jellyfish".[8][9]

A group of jellyfish is sometimes called a bloom or a swarm.[10] "Bloom" is usually used for a large group of jellyfish that gather in a small area, but may also have a time component, referring to seasonal increases, or numbers beyond what was expected.[11] Another collective name for a group of jellyfish is a smack,[12] although this term is not commonly used by scientists who study jellyfish. Jellyfish are "bloomy" by nature of their life cycles, being produced by their benthic polyps usually in the spring when sunshine and plankton increase, so they appear rather suddenly and often in large numbers, even when an ecosystem is in balance.[13] Using "swarm" usually implies some kind of active ability to stay together, which a few species such as Aurelia, the moon jelly, demonstrate.[14]

Medusa jellyfish may be classified as scyphomedusae ("true" jellyfish), stauromedusae (stalked jellyfish), cubomedusae (box jellyfish), or hydromedusae, according to which clade their species belongs.[15]

In biology, a medusa (plural: medusae) is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below. The upper or aboral surface is called the exumbrella and the lower surface is called the subumbrella; the mouth is located on the lower surface, which may be partially closed by a membrane extending inward from the margin (called the velum). The digestive cavity consists of the gastrovascular cavity and radiating canals which extend toward the margin; these canals may be simple or branching, and vary in number from few to many. The margin of the disk bears sensory organs and tentacles as its said.

German biologist Ernst Haeckel popularized medusae through his vivid illustrations, particularly in Kunstformen der Natur.

Anatomy

The major surfaces and axes of a jellyfish

Most jellyfish do not have specialized digestive, osmoregulatory, central nervous, respiratory, or circulatory systems. The manubrium is a stalk-like structure hanging down from the centre of the underside, with the mouth at its tip. This opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. It is joined to the radial canals which extend to the margin of the bell.[16] Jellyfish do not need a respiratory system since their skin is thin enough that the body is oxygenated by diffusion. They have limited control over movement, but can use their hydrostatic skeleton to navigate through contraction-pulsations of the bell-like body; some species actively swim most of the time, while others are mostly passive.[citation needed] The body is composed of over 95% water; most of the umbrella mass is a gelatinous material — the jelly — called mesoglea which is surrounded by two layers of protective skin. The top layer is called the epidermis, and the inner layer is referred to as gastrodermis, which lines the gut.

Nervous system

Jellyfish have no brain nor central nervous system, but employ a loose network of nerves, located in the epidermis, which is called a "nerve net".[17] A jellyfish detects various stimuli including the touch of other animals via this nerve net, which then transmits impulses both throughout the nerve net and around a circular nerve ring, through the rhopalial lappet, located at the rim of the jellyfish body, to other nerve cells.

Another counter to the "brainless jellyfish" hypothesis[clarification needed] is that some species explicitly adapt to tidal flux to control their location. 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 waiting for the tide to rise, ascending and allowing it to sweep them back into the bay. They monitor salinity to avoid fresh water from mountain snowmelt, again by diving until they find enough salt.[2]

Vision

Some jellyfish have ocelli: light-sensitive organs that do not form images but which can detect light, and are used to determine up from down, responding to sunlight shining on the water's surface. These are generally pigment spot ocelli, which have some cells (not all) pigmented.

Certain species of jellyfish, such as the Box jellyfish, have been revealed to be more advanced than their counterparts. The Box jellyfish has 24 eyes, two of which are capable of seeing color, and four parallel information processing areas or rhopalia that act in competition,[18] supposedly making it one of the few creatures to have a 360 degree view of its environment.[19] It is suggested that the two eyes that contain cornea and retina are attached to a central nervous system which enables the four brains to process images. It is unknown how this works, as the creature has a unique central nervous system.[2]

The eyes are suspended on stalks with heavy crystals on one end, acting like a gyroscope to orient the eyes skyward. They look upward to navigate from roots in mangrove swamps to the open lagoon and back, watching for the mangrove canopy, where they feed.[2]

Size

The lion's mane jellyfish Cyanea capillata is one of the larger species of jellyfish.

Jellyfish range from about one millimeter in bell height and diameter to nearly two meters in bell height and diameter; the tentacles and mouth parts usually extend beyond this bell dimension.

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which have bell disks from 0.5 mm to a few mm diameter, with short tentacles that extend out beyond this, on which these tiny jellyfish crawl around on seaweed or the bottoms of rocky pools.[20] Many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope; they can reproduce asexually by splitting in half (called fission). Other very small jellyfish, which have bells about one mm, are the hydromedusae of many species that have just been released from their parent polyps;[21] some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living for months, yet never growing beyond a few mm in bell height and diameter.[22] Another small species of jellyfish is the Australian Irukandji, which is about the size of a fingernail.[2]

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 metres (120 ft) long (though most are nowhere near that large).[23][24] They have a moderately painful, but rarely fatal, sting. Claims that this jellyfish may be the longest animal in the world are likely exaggerated; some other planktonic cnidarians called siphonophores may typically be tens of meters long and seem a more legitimate candidate for longest animal.

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 probably a much better candidate for "largest jellyfish", since the largest Nomura's jellyfish in late autumn can reach 200 centimetres (79 in) in bell (body) diameter and about 200 kilograms (440 lb) in weight, with average specimens frequently reaching 90 centimetres (35 in) in bell diameter and about 150 kilograms (330 lb) in weight.[25][26] The large bell mass of the giant Nomura's jellyfish[27] can dwarf a diver and is nearly always much greater than the up-to-100 centimetres (39 in) bell diameter Lion's Mane.[28]

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea is another solid candidate for "largest jellyfish", with its thick, massive bell up to 100 centimetres (39 in) wide, and four thick, "strap-like" oral arms extending up to 6 metres (20 ft) in length,[29] very different from the typical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion's Mane.

Classification and evolution

Medusa jellyfish are a life stage exhibited in some species of the phylum cnidaria. Medusa jellyfish belong exclusively to medusozoa, the clade of cnidarians which excludes anthozoa (e.g., corals and anemones). (This suggests that the medusa form evolved after the polyps.)[30]

The phylogenetics of this group are complex and still being worked out. Some progress has been made: the Medusozoa appear to be a sister group to Octocorallia.[31] Staurozoa appears to be the earliest diverging; Cubozoa and the coronate Scyphozoa form a clade that is the sister group of Hydrozoa plus discomedusan Scyphozoa. The Hydrozoa are the sister group of discomedusan Scyphozoa. Limnomedusae (Trachylina) is the sister group of hydroidolinans. This group may be the earliest diverging lineage among Hydrozoa. Semaeostomeae is a paraphyletic clade with Rhizostomeae.

There are four major classes of medusozoan cnidaria:

  • Scyphozoa are often called true jellyfish. They have tetra-radial symmetry. They have tentacles around the outer margin of the bowl-shaped bell, and oral arms around the mouth.
  • Cubozoa (box jellyfish) have a box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to "true jellyfish" than either are to hydrozoa.[30]
  • Hydrozoa may form medusa which resemble scyphozoans (but generally with a velum) and are distinguished by an absence of cells in the mesoglea. However, many hydrozoa species do not form medusa at all (such as hydra, which is hence not considered a jellyfish).
  • Staurozoa (stalked jellyfish) do not have a polyp stage, however the medusa is generally sessile, oriented upside down and with a stalk from the "bell" planted to the substrate. Until recently, staurozoa was classified within scyphozoa.

Some other animals are frequently associated with or mistaken for medusa jellyfish.

  • Siphonophorae are an order of hydrozoa which generally live as colonies (for example, free-swimming chains of repeated units, some units similar to polyps or to medusa). They are not considered medusa jellyfish. A well-known example is the Portuguese Man o' War.
  • Ctenophores (comb jellies) are a separate phylum from cnideria. Their method of propolsion is cillia paddles rather than a pulsating bell.
  • Salps are transparent, gelatinous marine organisms that form pelagic colonies like siphonophores. Salps are chordates, and as such are actually more closely related to humans than they are to cnidarians and comb jellies.[32]

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 20 species of Cubozoa, and in Hydrozoa there are about 1000–1500 species that produce medusa (and many more hydrozoa species that do not).[33][34]

Life-cycle

See also: Biological life cycle and Developmental biology
Illustration of two life stages of seven jelly species.
The developmental stages of scyphozoan jellyfish's life cycle:
1–3 Larva searches for site
4–8 Polyp grows
9–11 Polyp strobilates
12–14 Medusa grows

Most jellyfish alternate between polyp and medusa generations during their life cycle. Additionally, there are several possible larval life-stages.

After fertilization a primitive free-swimming larval form, called the planula, develops. The planula is a small larva covered with cilia. It settles onto a firm surface and develops into a polyp. Some polyps can also asexually produce a creeping frustule larval form, which then also develops into a new polyp.

The polyp is generally a small planted stalk with a mouth that is ringed by upward-facing tentacles. The polyps are like miniatures of the closely related anthozoan (sea anemones and corals) polyps, which are also members of Cnidaria. The jellyfish polyp may be sessile, living on the bottom or another substrate such as floats or boat hulls, or it may be free-floating or attached to tiny bits of free-living plankton[35] or rarely, fish[36] or other invertebrates. Polyps may be solitary or colonial. Polyp colonies form by strobilation, resulting in multiple polyps which share a common stomach cavity.[37] Most polyps are very small, measured in millimeters. They feed continuously. The polyp stage may last for years.

Eventually the polyp gives rise to the medusa stage. New medusae are usually created asexually by strobilation or budding from the polyp. The medusa is the life stage which is most typically identified as a jellyfish.

Reproduction

Jellyfish reproduce both sexually and asexually. Upon reaching adult size, jellyfish spawn daily if there is enough food. In most species, spawning is controlled by light, so the entire population spawns at about the same time of day, often at either dusk or dawn.[38] Jellyfish are usually either male or female (hermaphroditic specimens are occasionally found).

In most cases, adults release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms. In a few species, the sperm swim into the female's mouth fertilizing the eggs within the female's 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.

After a growth interval, the polyp begins reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. New scyphistomae may be produced by budding or form new, immature jellies called ephyrae. A few jellyfish species can produce new medusae by budding directly from the medusan stage. Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. A few species of hydromedusae reproduce by fission (splitting in half).[35]

In the second stage, the tiny polyps asexually produce jellyfish, each of which is also known as a medusa. Tiny jellyfish (usually only a millimeter or two across) swim away from the polyp and then grow and feed in the plankton.[citation needed] Medusae have a radially symmetric, umbrella-shaped body called a bell, which is usually supplied with marginal tentacles – fringe-like protrusions from the bell's border that capture prey. A few species of jellyfish do not have the polyp portion of the life cycle, but go from jellyfish to the next generation of jellyfish through direct development of fertilized eggs.[citation needed]

Most jellyfish have a second stage to their life cycle, the planula larvae phase, following the initial egg and sperm phase. Although this is a short lived stage for jellyfish, it is an important phase when the fertilized eggs that had previously undergone embryonic development, hatch, and planulae emerge from the females mouth or brood pouch and are off on their own.[39]

Lifespan

Jellyfish lifespans typically range from a few hours (in the case of some very small hydromedusae) to several months. Life span and maximum size varies by species. Jellyfish held in public aquariums are carefully tended, fed daily even when food might be seasonally rare in the wild, and sometimes treated with antibiotics if they develop infections, so may live several years, though this would be very unusual in the sea. Most large coastal jellyfish live 2 to 6 months, during which they grow from a millimeter or two to many centimeters in diameter. One unusual species is reported to live as long as 30 years[citation needed]. Another unusual species, T. nutricula, falsely reported as Turritopsis dohrnii, might be effectively immortal because of its ability under certain circumstances in the laboratory 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 ocean organism .[40] So far this transdifferentian of life form has been observed only in the laboratory and it is not known if it actually occurs in wild Turritopsis populations.

Ecology

Feeding

Jellies are carnivorous, feeding on plankton, crustaceans, fish eggs, small fish and other jellyfish, ingesting and voiding through the same hole in the middle of the bell. Jellies hunt passively using their tentacles as drift nets.

Predation

Other species of jellyfish are among the most common and important jellyfish predators, some of which specialize in jellies. Other predators include tuna, shark, swordfish, sea turtles and at least one species of Pacific salmon. Sea birds sometimes pick symbiotic crustaceans from the jellyfish bells near the sea's surface, inevitably feeding also on the jellyfish hosts of these amphipods or young crabs and shrimp.

Blooms

Photo of translucent moon jelly on black blackground. The jelly contains a white gamsana mass extending through about 2/3 of its body
Aurelia sp. occurs in large quantities in most of the world's coastal waters. Members of this genus are nearly identical to each other.
Map of population trends of native and invasive species of jellyfish[41]
  Increase (high certainty)
  Increase (low certainty)
  Stable/variable
  Decrease
  No data

Jellyfish bloom formation is a complex process that depends on ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentrations. Ocean currents tend to congregate jellyfish into large swarms or "blooms", consisting of hundreds or thousands of individuals. Blooms can also result from unusually high populations in some years. 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 relatively better able to survive in warmer waters.[42]

Scientists have little historic data about jellyfish populations.[13]

One hypothesis is that the global increase in jellyfish bloom frequency may stem from human impact. In some locations jellyfish may be filling ecological niches formerly occupied by now overfished creatures, but this hypothesis lacks supporting data.[13] Youngbluth states that "jellyfish feed on the same kinds of prey as adult and young fish, so if fish are removed from the equation, jellyfish are likely to move in."[43]

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).[44][45] Invasive populations can expand rapidly because they often face no predators in the new habitat.

Increased nutrients, ascribed to agricultural runoff, have been cited as contributing to jellyfish proliferation. Graham states, "ecosystems in which there are high levels of nutrients ... provide nourishment for the small organisms on which jellyfish feed. In waters where there is

very few will kill you but they give intense pain
Jellyfish stings | Ministry of Health NZ
Home > YourHealth topics > Bites and stings > Jellyfish stings

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Information from the UK National Health Service.

Jellyfish stings

There are several kinds of jellyfish found in New Zealand – and some can deliver a painful sting. Find out which jellyfish to watch out for, and what to do if you or a family member gets stung.

Photo of a lion’s-mane jellyfish, a large, pale blue jellyfish with many tentacles.
Lion’s-mane jellyfish, photo by Jérôme Mallefet / CC BY-NC-SA 3.0.

Photo of a mauve stinger, a purple jellyfish with several large tentacles hanging from the bell, and a few thinner catch tentacles.
Mauve stinger, photo by Hans Hillewaert / CC-BY-SA-3.0.

Photo of a washed up blue bottle, with a pale blue body which looks like you could pop it, and blue tentacles.
Washed-up blue bottle, photo by Pappito at en.wikipedia / CC-BY-SA-3.0.

The lion’s-mane jellyfish is a common stinging jellyfish. It can be found in colours from white to deep blue. It grows to almost 2 m across. Its tentacles can be up to 5 m long and are almost invisible.

The mauve stinger has only few stinging catch tentacles. It can grow to 40 cm across.

The Portuguese man-of-war (blue bottle) has a burning sting. It’s not a true jellyfish, which means there are some things you should do differently to treat the sting. These are described below.

Call 111 for an ambulance if you or someone else has been stung and has symptoms of a serious allergic reaction or anaphylaxis.

These symptoms include:

  • swelling around the lips and eyes
  • rapid development of a rash
  • shortness of breath or wheezing
  • chest tightness
  • severe dizziness or faints
  • persistent sneezing or coughing
  • hoarse voice
  • difficulty swallowing or throat tightness
  • signs of shock (pale skin, rapid pulse and fainting).

Self care for jellyfish stings

If you or a family member has been stung by a jellyfish, get out of the water and follow these steps.

  • Apply wet sand or a towel soaked in sea water. If tentacles are still sticking to your skin, don’t try to pull them off.
  • If you are able to warm up some sea water, pour this over the area (even urine is better than nothing!). If you can get vinegar, pour this over the stung area (but do not use vinegar for blue bottle stings).
  • Do not apply fresh water as this will activate the stingers.
  • Wait five minutes and then wipe the tentacles off with a dry towel. Be careful not to get stingers on your hands – wear gloves if you have some.
  • For all stings except blue bottles, apply cool compresses to the affected skin.
  • For blue bottle stings, immerse the stung area in warm water (45°C) for 20 minutes.
  • Elevate the affected area for 24 hours.
  • If necessary, take pain relief such as Panadol.
  • Antihistamines such as Telfast, Claratyne and Phenergan may relieve itching and swelling. A cream with hydrocortisone will reduce inflammation. You can get these from your pharmacy.

Medicine precautions

  1. Do not give aspirin (acetylsalicylic acid) or aspirin-containing products to anyone 18 years or younger because of the risk of a serious illness called Reye's syndrome.
  2. Take non-steroidal anti-inflammatory drugs (NSAIDs) with food or milk to prevent stomach irritation. Do not give NSAIDs to anyone with:
    • NSAID-induced asthma
    • increased risk of bleeding, such as ulcer disease, a bleeding disorder, if taking blood thinners (anticoagulants), or following surgery, significant trauma or major dental work
    • an allergy to NSAIDs.

When to see your doctor

Call your doctor if you have been stung and have:

  • increasing numbness or difficulty breathing
  • signs of poisoning: abdominal pain, muscle cramps, nausea, vomiting
  • signs of infection later: increasing pain, redness, swelling, red streaks leading away from the sting, heat, discharge of pus, fever or chills
  • pain that is not controlled by following the self-care instructions
  • any new or worsening symptoms.

Page last updated: 02 August 2012

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they are found in nz or austraila

The Bluebottle Jellyfish The blue bottle feeds on small fish and other small ocean creatures. They envelope their prey with their tentacles, where a poison is released thus paralysing its prey before being consumed. The tentacles adhere extremely well to their prey. If a tentacle is put under the microscope you will see that it looks like a long string of barbed hooks, which explains the ability of the tentacle to attach. If a tentacle attaches itself to a human, it releases a poison (through the use of nematocysts), and if you continue to rub the skin after the tentacle has been removed more poison or venom will be released. If you are stung, it is best to wash the area without touching. A cold pack should be used to relieve the pain. If stung, please consult a doctor immediately. No fatalities have ever been reported within Australia or New Zealand from the sting of a blue bottle. The blue bottles colour can range from a blue to a pink hue, with a transluscent body. The float or body of the blue bottle measures between 3 to 15 cms. The tentacles can range in length from 15 cms up to 10 metres!. The way it stings is by as shown here it puts its tentecals around it and stings it If stung you look like this man above Also it will float round like this it will float round with its tentacals trailing behind it This jellyfish is actually made up of zooids. The blue bottle is not a single organism, but made up of a number of zooids. Each zooid has a specific role and together they function as if it were an animal. For example a number of zooids will make up the stinging tentacles, others will make up the feeding tentacles. It will only sting people if it thinks its under attack and will only sting its prey purposely. It stinging humans is its own form of defence In Australia and New Zealand, this jellyfish is known as the blue bottle, due to its colour and shape when strewn on a beach. Elsewhere in the world it is known as the "Portuguese Man o War" as it is said to look like a Portuguese battleship with a sail. A washed up bluebottle The thing that made me want to do this was at brighton beach there was tons of blue bottles washed up on the shore