KINDS OF JELLYFISH
By some estimates there are 200 species of jellyfish. They range in size from tiny transparent hydromedusae. a few millimeters across, to giant red-and-purple deep sea varieties, that reach two meters (6-feet) across and have 30-meter (100-foot) -long tentacles. Some jellyfish reportedly have tentacles that reach 60 meters (200 feet) in lenth.
Jellyfish live in almost every ocean habitat: in tropical reefs, under polar icecaps and in ocean trenches. Many jellyfish produce bioluminescence (See bioluminescence). About 70 produce a sting that can be harmful to humans.
Jellyfish with a fringed dome with stinging tentacles are called a medusas. They are named after a woman from a Greek myth who was loved by Poseidon, the God of the Sea, and for this was changed by a jealous goddess into a beast with snakes for hair.
Cassiopea jellyfish, known as upside-down jellyfish for their preferred position, appear to sleep at night. Cassiopea jellies prefer sitting to swimming, so the suspended jellies pulsed their way down to ocean substrates, or the tank floor in labs. The evidence that they sleep comes from research that shows they descend much much faster during the day, starting to pulse by 2 seconds after losing their resting surface, than they do at night, when it takes them about 6 seconds to start pulsing — “almost as if they were groggily shaking off sleep before they could react” according to Live Science (See Jellyfish Characteristics and Behavior). [Source: Stephanie Pappas, Livescience, September 22, 2017]
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
The elusive immortal jellyfish (Turritopsis dohrnii) is said to age backward and has the theoretic potential to live forever. . When threatened, this glowing bell-shaped invertebrate can revert to its earliest life phase — essentially restarting its life. [Source: National Geographic]
According to Live Science: No bigger than a pinky nail, these translucent blobs can turn back their biological clocks when injured and revert into plant-like polyps sprouting from the ocean floor. If enough of these polyps colonize, they can eventually begin to bud and "release medusae that are genetically identical to the injured adult," according to the American Museum of Natural History. [Source: Jennifer Nalewicki, Live Science, March 31, 2023]
Technically immortal jellyfish are actually hydrozoas not true jellyfish According to Business Insider: As the jelly ages, it eventually settles onto the sea floor and becomes a colony of polyps (individual organisms). The polyps then spawn new, genetically identical jellyfish. If a Turritopsis dohrnii gets physically harmed or starts to starve, it can transform back into a polyp at will — then in turn produce new, genetically identical jellyfish.[Source: Zoë Miller,Azmi Haroun, Business Insider, December 25, 2022]
Immortal jellyfish are found worldwide in temperate to tropic waters. Like most other hydrozoans, they begin their lives as tiny, free-swimming larvae known as planulae. As a planula settles down, it gives rise to a colony of polyps that are attached to the sea floor. All the polyps and jellyfish arising from a single planula are genetically identical clones. The polyps form into an extensively branched form, which is not commonly seen in most jellyfish. [Source: Wikipedia
Immortal jellyfish begin their life anew through the cell development process of transdifferentiation, which alters the differentiated state of the cells and transforms them into new types of cells. Theoretically, this process can go on indefinitely, effectively rendering the jellyfish biologically immortal, although in practice individuals can still die. In nature, most of them likely to succumb to predation or disease in the medusa stage without reverting to the polyp form.
Lion’s Mane Jellyfish — the World’s Biggest Jellyfish
The lion’s mane jellyfish (Cyanea capillata) is the largest and longest jellyfish species. The largest known specimen stretched for 36.5 meters (across 120 feet) from its top to the bottom of its tentacles. The creature is difficult to weigh as it so blobby and 95 percent water. Its tentacles contain large amounts of neurotoxins that can cause a range of effects when humans come in contact with them, ranging a rash to respiratory difficulties. Humans don't often come in contact with them because they tend to be found in the open ocean and not near coasts. Lion’s mane jellyfish are not endangered or threatened They have “No special status” on the International Union for Conservation of Nature (IUCN) Red List: [Source: Smithsonian]
Lion’s mane jellyfish can be found in the cooler regions of the Atlantic, Pacific, North Sea and Baltic. They are especially prevalent near the east coast of Britain. They are found in the pelagic (open ocean) zone as medusae and then benthic (ocean floor) zone as polyps. They are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), have radial symmetry (symmetry around a central axis). Among the most distinguishing features of Lion’s mane jellyfish is brigh orange and pink its coloration and its tendency to form large schools. Kilometer-long shoals of them form off the coast of Norway and in the North Sea. Cyanea can be dangerous to swimmers when contact occurs, but they do not actively seek out humans. The toxins in its nematocysts can be quite powerful, capable of stinging after the jellyfish is dead or the tentacle has been emoved. . [Source: Blayne Naylor, Animal Diversity Web (ADW)]
According to Animal Diversity Web (ADW): This member of the giant jellyfish has a hemispherical bell with scalloped edges. The bell is divided into eight obvious lobes by eight indentations with second order indentations. Some lobes contain sense organs including odor pits, balance organs, and simple light receptors. Its bell normally ranges in diameter from 30 to 80 centimeters, with some individuals growing up to a maximum of 180 centimeters. The oral arms are purple with reddish or yellow tentacles, hence the common name "Lion's Mane". The bell may be pink to reddish-gold or brownish-violet. The jellyfish has no fringing tentacles around the edge of its bell, but it has eight groups of 150 tentacles each on the underside of its umbrella. These tentacles contain very effective nematocysts, as does the upper surface of the jellyfish. /=\
Lion’s mane jellyfish are continual swimmers that can reach speeds of up to several kilometers per hour and can cover great distances with the aid of marine currents. They feed mainly on fish and hunt prey by sinking slowly with their tentacles spread in a circle around it. The prey is captured in the "net" of tentacles and stunned by the nematocysts.
The medusa form of the jellyfish reproduces sexually and has separate sexes. The ova and sperm are produced in baglike projections of the stomach wall. The sex cells are relased through the mouth for external fertilization. In the case of Cyanea, the eggs are held in the oral tentacles until the planula larvae develop. There is no parental involvement in the raising of offspring. The planula larvae then settle on the substrate and develop into polyps. These scyphopolyps reproduce asexually by horizontal division (strobilation) and are then termed strobila. With each division, a small disk forms, and when multiple disks have formed, the uppermost one detaches and swims off as a ephyra. The ephyra develops into the recognized medusa form of the jellyfish. /=\
10-Meter Giant Phantom Jellyfish Lives at Depths of 6.7 Kilometers
One of the largest jellyfish in the world, the giant phantom jellyfish (Stygiomedusa gigantea) is also one of the deepest living. It is rarely seen but one was photographed and video at a depth in 1,000 meters (3,300 feet) Monterey Bay, California by a remote-controlled submarine in 2021. In the video the “scarlet jellyfish is seen bobbing along with its bell-shaped head and four long, flowing arms that resemble a kite's ribbon tails...The giant jellyfish's large bell is seen pulsing and glowing a faint orange as it floats in the dark abyss. [Source: Elizabeth Gamillo, Smithsonian.org, December 14, 2021
According to the Smithsonian: Giant phantom jellies truly live up to their name: The creature's bell can be up to one meter (three feet) wide, and its arms reach lengths of 10 meters (33 feet). Although they are quite big, they're actually rather hard to find. Since it was first discovered by scientists in 1899, the highly elusive creature has only been observed about 100 times in total, per Live Science. Despite completing thousands of dives, Monterey Bay Aquarium Research Institute (MBARI) scientists have documented the species about nine times in the wild.
One reason these deep sea creatures are hard to find is that they lurk 6.8 kilometers (4.1 miles) below the surface. This depth of the ocean is called the midnight, or bathypelagic zone. Water pressure reaches up to 5,800 pounds per square inch at these depths, but jellies can survive these tremendous pressures because their soft gelatinous bodies absorb them. While much is unknown about the giant phantom, researchers suspect it uses its long, drape-like, "oral arms" to tangle up prey and bring it up to its mouth, Colossal reports. MBARI scientists also observed pelagic brotula (Thalassobathia pelagica) darting in and around the jellyfish's flowing body, a statement explains. Despite such close proximity to the jelly's mouth, some creatures may hide among its tentacles and large billowing head for safety in the open waters of the midnight zone.
Sea nettles (Scientific name: Chrysaora quinquecirrha) are a common type of jellyfish commonly seen off the east coast of the United States. Also known as the Atlantic sea nettle or East Coast sea nettle, they are broadly dispersed in tepid waters along the coasts of the Atlantic and Indian Oceans, as well as the Western Pacific. Along the United States east coast they are common to abundant from southern New England to as far south as Brazil. In Virginia waters these jellyfish first appear in May, and come and go and stick around until September, though some occasionally remain well into November.
Sea nettles are native to the Indian Ocean and Atlantic Ocean and have been introduced to the Pacific Ocean. They are common in temperate waters and Atlantic estuaries which are low in salinity. In the Chesapeake Bay they are abundant from July through August, and make their way into creeks and rivers.[Source: Nate Lanier and Alexi Weber, Animal Diversity Web (ADW) /=]
sea nettles The body of an adult sea nettle is an opaque white color, often with red streaks or dots visible through the cup and tentacles. The tentacles have an average length of 50 centimeters (20 inches). Their dome-shaped body has an average width of 25 centimeters (10 inches). Atlantic sea nettles feed on zooplankton, ctenophores, as well as other jellies and occasionally eat small crustaceans, comb jellies, and fish eggs and larvae. Very few animals feed on these jellies since they are covered with stinging cells and have toxic venom. Their main known predators are Leatherback turtles, Ocean sunfish and other jellyfish.
Sea nettles are considered a keystone species, meaning their presence or absence strongly affects populations of other species in area where they live. Feeding on ctenophores, Sea nettles eliminates the main predator of copepods, thus positively influencing their abundance. Not only does a higher concentration of copepods benefit planktonic populations, it also benefits fish species that prey on plankton.
Sea Nettle Behavior and Reproduction
Sea nettles are diurnal (active during the daytime), sessile (fixed in one place) motile (move around as opposed to being stationary), solitary social colonial (living together in groups or in close proximity to each other). Hibernation is the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. [Source: Stephanie Braccini, Animal Diversity Web (ADW) /=]
Sea nettles breeds during the summer months. The and the age in which they become independent ranging from 15 (low) hours and the average time to independence is 20 hours. Fertilized eggs will remain attached to the female parent's oral arms. The eggs into planula on the arms. Once the polyps develop fully into flower-shaped progeny, they are released into the ocean where they settle.
Sea nettles are polygynandrous (promiscuous), with both males and females having multiple partners. What attracts or induces the Atlantic sea nettle to reproduce is known. This species reproduces both sexually and asexually. Parental care and pre-fertilization, pre-birth, pre-weaning and pre-independence protection are provided by females. Sea nettles are altricial. This means that young are born relatively underdeveloped and are unable to feed or care for themselves or move independently for a period of time after birth. /=\
Polyp stages of Sea nettles can remain sessile or float freely. According to Animal Diversity Web: Asexual budding from sessile polyps can lead to colonial, formation in the species. As medusa, the jellies move vertically and swim almost constantly. Vertical column distributions and swim patterns change in direct correlation with prey densities. This suggests hunting patterns are intrinsically linked to swimming. In-situ observations showed this species constantly swimming and propose it be considered a cruising predator.
When observed in nature with minimal interference, the average time spent swimming within 24 hours was recorded from 90 percent and 100 percent. The swimming patterns witnessed were highly directional and non-random. With the ability to sense light and dark, medusae can determine their location and alignment in the water.
The jellies also tend to swim against the current. As a result, they can become concentrated in large numbers, which make them coincidentally colonial (living together in groups or in close proximity to each other).
The disappearance of Atlantic sea nettles around the Chesapeake Bay area in winter months appears to be from their inability to swim away from the sea bottom. Cold water impedes and slows the jelly's ability to pulsate the swimming bell. This can lead to starvation, and usually concludes with large biomass deposits on the sediment surface.
Moon jellyfish are also called common jellyfish. These common names can refer to two species: 1) Aurelia labiata, which inhabits the coastal regions of the eastern Pacific Ocean from southern California, to Prince William Sound, Alaska; and 2) its close relative Aurelia aurita, which has a worldwide distribution, and is typically observed in coastal waters. Moon jellyfish adapt readily to tank life and are fixtures of both public and home aquariums. In the wild they exist in large numbers and there a no worries about them being threatened or endangered. [Source: Chelsea Macentimetersullan, Animal Diversity Web (ADW) /=]
Moon jellyfish are typically found at depths of zero to 1000 meters (3280.84 feet). They float near the surface in warm nearshore waters and are especially prevalent in bays and harbors. Despite this they are often referred to as pelagic (open ocean). Aurelia aurita can survive in waters ranging from -6̊ to 31̊C (21̊ to 88̊F). Their lifespan in the wild is typically around one year. Moon jellyfish polyps usually become strobilates early in spring, and become medusa and mature very quickly, spawn, and die by midsummer or early fall. /=\
The moon jellyfish sting is mild and does not harm humans. Their main known predators are lion's mane jellyfish. Moon jellyfish play an important role in marine ecosystems as consumer of marine zooplankton and sometimes compete with fish, which also feed on marine zooplankton. Moon jellyfish sometimes appear in groups with hundreds to millions of individuals. These aggregations have been widely studied in Prince William Sound, Alaska, and the evidence suggests the groups form because the jellies get stuck in currents and flow features of the water column. Reduced swimming due to collisions amongst the medusae in crowded areas is believed to assist in maintenance of the aggregations.
Moon Jellyfish Physical Characteristics
Moon jellyfish range in length from 10 to 45 centimeters (4 to 18 inches). Sexual dimorphism (differences between males and females) is minimal: Both sexes are roughly equal in size and look similar; but are sexes colored and patterned a little differently. [Source: Chelsea Macentimetersullan, Animal Diversity Web (ADW) /=]
Moon jellyfish are venomous, ectothermic, (use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment), have radial symmetry (symmetry around a central axis).
According to Animal Diversity Web: The translucent, moonlike bell that is characteristic of Moon jellyfish has earned Moon jellyfish their common name. They do not have the long trailing tentacles that people usually associate with jellyfish. Instead, they have a fine fringe lining the bell margin. The body form of Moon jellyfish is distinguished from close relatives in the genus Aurelia by an enlarged, fleshy manubrium, four oral arms protruding from the base of the manubrium, planulae (ciliated fertilized egg) brooding on the manubrium, and secondary scalloping of the bell margin between rhopalia, forming 16 notches. Bells of juveniles and young adults are translucent, and with maturity they turn milky white, sometimes with a pink, purple, peach, or blue tint.
Eastern Pacific Moon Jellyfish Populations
Eastern Pacific moon jellyfish can easily be divided into three geographical morphotypes. According to Animal Diversity Web: The southernmost form, found in California from San Diego to Marina del Ray, has a manubrium that is a wide, rounded frill. The radial canals range in number, depending on age. The oral arms are typically straight. Planulae range in color from white to bright orange, and the bells are colorless to milky white. Male sex organs are dark purple, and female sex organs are pale pink. Southern Moon jellyfish grow to a maximum of 35 centimeters. /=\
The central form inhabits coastal waters from Santa Barbara, California, to Newport, Oregon. Abundant in late summer, central Moon jellyfish have an elongated manubrium that is rectangular and tapering. The radial canals are very numerous, and the oral arms are straight or bent counter-clockwise. The planulae are lavender, and medusae found in Monterey, California, are usually purple, while those found in Santa Barbara are often pale pink. Male sex organs are dark purple, and female sex organs are brown. Individuals of the central form of Moon jellyfish have been recorded as high as 45 centimeters. /=\
The northernmost form, ranging from Puget Sound, Washington, to Prince William Sound, Alaska, have a pyramidal manubrium. The many parallel radial canals of adults give the bell a lacy appearance. The oral arms are generally straight, and the planulae are found in variable colors. The bells are peach or whitish, male sex organs are dark purple, and female sex organs pale brown. Northern Moon jellyfish range in size from 14-29 centimeters. /=\
Moon Jellyfish Reproduction and Development
Moon jellyfish reproduce using internal fertilization. According to Animal Diversity Web: The sex organs are one of the most recognizable characteristics of the animal. They are horseshoe shaped organs with deep coloration that can be seen in the center of the bell. In the mating season, males are seen with sperm filaments attached to their oral arms. Sperm is carried to the gastric pouch of the female by cilliary currents. Females hold the fertilized eggs, which appear as grey clumps, on the manubrium. [Source: Chelsea Macentimetersullan, Animal Diversity Web (ADW) /=]
Aurelia aurita is known to reach sexual maturity in the spring and summer. In these seasons much of the organism's energy is devoted to reproduction. As the jellies live in close aggregations, complex mating rituals do not exist, males simply release their sperm filaments during the period of sexual maturity, which are carried to the female sex organs by ciliary currents.
Male and female medusa spawn into the sea where the eggs are fertilized. The fertilized egg is called a planula, a cilliated organism that is elliptical and elongated. The planulae are brooded on the manubrium of Moon jellyfish. They are shaken off and attach to a substrate, usually hanging upside-down from the underside of docks, mussel shells, or rocks. There they transform into a polyp 2-3 millimeters in height, with an oral disk 1-2 millimeters in diameter. Polyps range in color from whitish to pale pink and orange. Polyps attached to a substrate asexually reproduce by side budding, stolon budding, or podocyst formation.
Eventually the polyp strobilates, meaning that it transforms into a stack of several organisms. In Moon jellyfish, the strobila are both monodisk (produced one at a time) and polydisk (several disks produced), with more than 20 developing ephyrae (free-swimming, immature medusae). Their color varies with location (cinnamon in Southern California and tan in Monterey). The strobilation time lasts for about seven days, and the ephyrae are released. Typical ephyrae are 2-3 millimeters when released, with eight marginal arms and nematocysts (stinging cells) on the exumbrellar surface. The ephyrae swim about until they develop into mature medusa form. (Gershwin, 2001) /=\
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023