Scyphozoa

(Jellyfish)

Phylum Cnidaria

Class Scyphozoa

Number of families 20

Thumbnail description
Large, soft-bodied, gelatinous marine invertebrates that swim by contracting their umbrella-shaped swimming bell and catch small prey by means of stinging tentacles

Evolution and systematics

The class Scyphozoa includes four orders, 20 families, 66 genera, and about 200 species. The four orders are Stauromedusae, the stalked jellyfish; Coronatae, the crown or grooved jellyfish; Semaeostomeae; and Rhizostomeae.

Animals in the phylum Cnidaria may have one or both of two body forms, the benthic polyp and the pelagic medusa. The four orders within the class Scyphozoa emphasize these two forms to different degrees. Specifically, in the order Stauromedusae, there is only a benthic stage, which is considered the medusa. In the orders Coronatae, Semaeostomeae, and Rhizostomeae both stages occur in most species, with the medusa stage being the largest and most conspicuous.

The phylum Cnidaria is considered to be of early evolutionary origin, but the position of the Scyphozoa relative to other cnidarian classes (Anthozoa [corals and anemones], Cubozoa [box jellyfish], and Hydrozoa [hydroids, hydromedusae, fire corals, and siphonophores]) is uncertain. It is debated whether the polyp or the medusa form is most primitive. The scyphozoans are related most closely to cubozoans, which were placed in the same class until recently. They have similar body forms and life cycles. The scyphozoans are related least to the Anthozoa. Molecular evidence suggests that Anthozoa represents the most primitive class in the phylum Cnidaria.

The fossil record of Scyphozoa is poor. Radially symmetrical impressions have been interpreted to be casts of primitive scyphomedusae. Recently, a large number of scyphomedusae that apparently were stranded and buried on a beach was discovered in central Wisconsin in the United States. Other fossil groups that may be ancient scyphozoan polyps are the conulariids, which were similar to modern coronate polyps and were present from the Ordovician to the late Triassic, and Bryonia from the Upper Cambrian and Ordovician, which is from the extinct order Bryoniida of the Scyphozoa.

Physical characteristics

Most species in the class Scyphozoa, excluding the order Stauromedusae, have two life stages, the predominant medusa stage (up to 80 in, or 2 m, in diameter) and the small, inconspicuous polyp stage (less than 0.13 in, or 4 mm, long). The medusa, or jellyfish, stage has a saucer- to umbrella-shaped body with two epithelial layers (epidermis and gastrodermis) separated by a thick layer of mesenchyme, a gelatinous connective tissue containing cells. Near the edge of the bell in the orders Coronatae and Semaeostomeae are tentacles used in

feeding. The tentacles have millions of microscopic intracellular organelles called nematocysts that evert a hollow thread from a capsule and may inject toxin into or entangle their small prey (zooplankton, fish eggs and larvae, or other gelatinous species). In the Semaeostomeae and Rhizostomeae, there are four oral or mouth arms on the underside (concave) of the bell, which also have stinging nematocysts for feeding. The polyps, called scyphistomae, can form colonies of individuals by budding or, in the case of coronate polyps, true colonies that have a chitinous sheath. Polyps are cup-shaped, attached to the substrate by a "foot," and with the central mouth surrounded by a single ring of tentacles with nematocysts.

Stalked jellyfish in the order Stauromedusae attach to seaweed or sea grasses by an aboral stalk. The main body (calyx) is funnel- or goblet-shaped and grows to 1.2 in (3 cm) wide, with eight arms, each bearing a cluster of as many as 100 short, clubbed tentacles. In the common genus Haliclystus, between each arm there is an adhesive disk, by which the animal can attach to move about. The gonads extend down the arms. The mouth is located at the inside center of the funnel-shaped body. Coloration varies; it may be shades of green, brown, yellow, or maroon and often matches the color of the substrate, making these jellyfish difficult to see. This form is considered the medusa stage, and there is no polyp or swimming stage.

Jellyfish in the order Coronatae have a deep groove around the aboral surface that separates the swimming bell into a central disk and a peripheral zone, which has lappets. One thick tentacle emerges between lappets on the upper surface of the bell; depending on the species, there are between eight and 36 tentacles. The mouth opens into a large, pouchlike stomach on the underside of the bell. Most of the species are deep living, and thus the central disk is colored dark red to maroon, making it invisible at depths and presumably concealing the bioluminescence emanating from consumed prey. Most of the medusae are small, less than 2 in (5 cm) in diameter or bell height, but some species may attain 6 in (15 cm) in diameter. The known polyps are colonial and covered with a chitinous sheath.

Adult jellyfish in the order Semaeostomeae generally are large, up to 80 in (2 m) in diameter, but usually less than 12 in (30 cm). The swimming bell is flat to hemispherical in shape. The bell edge may have lappets, or it may be smooth. From eight to hundreds of tentacles are present at the bell margin or beneath the bell. In the center of the concave side of the bell are four diaphanous or frilled oral arms that lead to the central mouth. The bell ranges from translucent to opaque and from white to dark orange in color, and it may have radiating stripes in some species. The polyp stage is small and may form groups of individuals by budding.

The rhizostome medusae also are large, up to 80 in (2 m) in diameter. The swimming bell is hemispherical and very firm in texture and lacks tentacles at the edge. The bell margin has eight or 16 lappets. The four oral arms of rhizostome medusae are fused and usually very elaborate, with many tiny tentacles and small mouths for feeding. There may be clublike projections from the oral arms. The medusae are translucent to opaque, with colors ranging from white to dark red; some have patterns that include stripes and spots. The polyp stage is small and may form clusters of individuals by budding.

Distribution

Scyphozoans are found in all marine waters. Most Stauromedusae are found in cool waters along temperate to sub-polar shorelines spring through autumn. Coronate medusae generally occur at great depths, where temperatures are a cool 40–46°F (5–8°C), but a few species occur in subtropical to tropical waters. Semaeostome species are the predominant large medusae in polar to temperate oceans, and they also inhabit subtropical and tropical waters. The scyphistomae of those species are active only in warm months; however, they can become dormant and survive through winter months. Rhizostome species live mostly in tropical waters, with only a few species found in subtropical or temperate regions. The medusae of shallow-living scyphozoans are seen during late spring to early autumn in surface waters of temperate to polar seas. In tropical waters and among deep-dwelling species, medusae may be present all year.

Habitat

Scyphozoan medusae are found from surface waters to abyssal depths, and the polyps are attached to hard surfaces, such as pilings, shells, and rocks, at various depths, depending on the species. Most Stauromedusae are seen at intertidal

down to shallow subtidal depths, usually attached to benthic plants (algae or sea grasses). One species is known from deep hydrothermal vent communities. Coronate medusae typically are found at mesopelagic depths (1,625–4,875 ft, or 500–1,500m), but a few species occur near the surface. Deep-living species may have polyps at abyssal depths, but the polyps of shallow-living species are on shallow substrates. Semaeostome and rhizostome medusae occur most abundantly near shore in surface waters above 165 ft (150 m), where food supplies are greatest. Their polyps also are found at shallow depths, often on the underside of structures away from direct light. Some semaeostome species are deep living, and their polyps generally are not known. There are no known deep-dwelling rhizostome species.

Behavior

Jellyfish behavior generally is simple, owing to their simple nervous system. Stauromedusae move around on the substrate by somersaulting, which they accomplish by alternating adhesion of the basal disc with that of tentacles or adhesive pads located between the tentacles of some genera. The most noticeable behavior of jellyfish is the rhythmic pulsation of the swimming bell, which moves them through the water for feeding and respiration. The swimming pulsations are coordinated by nerve centers around the edge of the bell. At the bell margin there also are sensory clubs (rhopalia), each consisting of a light-sensing organ (ocellus) and a gravity-sensing organ (statocyst); thus, medusae can sense light and dark and can determine their orientation in the water column. Semaeostome and rhizostome jellyfish swim continuously. This is important for oxygen exchange, which occurs over the entire body surface, and for feeding. The swimming of several species is known to be against flow in the water column; the result is that they all swim in the same direction and may become concentrated in convergences, like bales of hay stacked up to dry. Some species move up in the water column at night and down in the day ("diel vertical migration"). The scyphistomae (polyps) are able to move by the so-called foot and its extensions. They feed when prey makes contact with their tentacles, which have nematocysts; the jellyfish contract the tentacles and bring the prey to their mouths.

Feeding ecology and diet

All scyphozoans feed with tentacles or tentacle-like projections that have millions of microscopic intracellular organelles called "nematocysts." Some nematocysts act to

paralyze or kill the prey, whereas others entangle them. Stauromedusae catch prey by the tentacles and fold the arm inward to bring the prey to the mouth. Many coronate medusae do not swim actively while feeding but instead remain nearly motionless with their tentacles extended above the bell. For semaeostome and rhizostome medusae, the pulsations of the swimming bell force water through the tentacles and create vortices that may bring prey into contact with the tentacles and oral arms. For semaeostome medusae, when a prey item is immobilized on a tentacle, the tentacle contracts and transfers the prey to an oral arm. The prey is moved by cilia up the inside of the folded oral arm to the mouth and into one of the four gastric (stomach) pouches, where short, fingerlike projections wrap around the prey and secrete digestive enzymes. For rhizostome medusae, prey capture is by the small tentacles on the oral arms, which transfer the prey to one of the many small mouths nearby.

Most species feed on small crustaceans that predominate in most habitats. Stauromedusae consume epibenthic crustaceans, including gammarid amphipods and harpacticoid copepods. Medusae in the other orders primarily eat abundant calanoid copepods but also eat other small zooplankton, such as cladocerans, larvaceans (= appendicularians), and chaetognaths. Many semaeostome species also feed on other gelatinous species, including scyphomedusae, hydromedusae, siphonophores, and ctenophores. It is of particular interest that several species are known to consume the eggs and larvae of fish. Thus, scyphomedusae may be detrimental to fish populations, both by consuming the zooplankton foods needed by fish larvae and zooplanktivorous fish species, like herring, and by feeding on the young fish directly.

Reproductive biology

Scyphozoans generally reproduce both asexually and sexually. The benthic forms, Stauromedusae and scyphistomae (polyps) of the other orders, reproduce asexually by budding new polyps or cysts from the body or foot. Scyphistomae, which are present in most species of all orders except Stauromedusae, also produce the medusa stage by an asexual budding process called strobilation. Strobilation typically takes place at a certain time of year and is triggered by environmental factors, which differ by species; these factors include rising (spring) or falling (autumn) temperatures or changes in light levels. During strobilation, the polyp undergoes transverse segmentation, forming one to several small medusae, called "ephyrae." The process requires days to weeks, depending on temperature.

The fully formed ephyrae break free by swimming pulsations. The ephyrae grow into sexually mature medusae over the course of a month or longer. The medusae of most species have separate sexes, but a few species are sequential hermaphrodites. The males and females are indistinguishable except by examination of the gonads. No mating occurs. Sperm strands are released into the water by males and are taken up by the females during feeding. The gonads surround the gastrovascular cavity, and eggs may be fertilized in the ovary or after they are released into the gastrovascular cavity. In most species the fertilized eggs develop into small ciliated larvae (planulae) that swim to a suitable substrate, attach, and develop into polyps. In some species, the planulae are retained (brooded) by the female before settlement. Some species lack a polyp stage.

Conservation status

No species of Scyphozoa is listed by the IUCN.

Significance to humans

Scyphozoan jellyfish have direct and indirect effects on humans, many of which are negative. Swimmers fear them for their painful stings. All jellyfish sting, but the stings of small specimens and those with short tentacles often are not painful to humans. The genera Chrysaora and Cyanea are known for painful stings. Scyphozoan stings are painful but not deadly. More painful and dangerous stingers are in the class Cubozoa (box jellyfish) and the class Hydrozoa (specifically, the Portuguese man of war, Physalia physalis).

Fish populations and commercial fisheries may be affected detrimentally by jellyfish. Jellyfish may occur in great abundance, and, if they are caught in fishing nets, their great weight may cause the nets to rip or the fish catch to be damaged. Jellyfish eat the pelagic eggs and larvae of fish as well as the small zooplankton prey of fish larvae and zooplanktivorous fish species. Therefore, jellyfish both eat fish and compete with them for food. Jellyfish also appear to be intermediate hosts for some parasites of fish. Jellyfish have been a nuisance to fish farms, where they break up on the fish impoundments and sting and kill the fish, and to power plants, where they may clog the cooling water intake screens, sometimes causing the plants to suspend operations. On the positive side for fish and fisheries, the juveniles of at least 80 species of fish, many of which are commercially important, associate with large jellyfish. While the relative advantages of such associations are not known, they are thought to benefit the fish partners most.

Jellyfish also have a place of value in human enterprise. In Japan and China jellyfish are an important food and have been exploited for more than 1,700 years. In China they are considered a culinary delicacy and are thought to have medicinal value. A multimillion-dollar commercial fishery exists for at least 10 species of rhizostome medusae throughout Southeast Asia, and a fishery for Stomolophus meleagris has been started in the Gulf of Mexico. The swimming bell of the jellyfish is processed in a mixture of salt and alum and packaged for distribution. The semidried jellyfish is rehydrated, desalted, blanched, and served in a variety of dishes. The prepared jellyfish has a special crunchy texture.

Owing to their great beauty and the relaxing effect of their swimming pulsations, jellyfish have been a great success as specimens in public aquariums and even as household pets. Over the past decade, considerable advances have been made in jellyfish husbandry, and several species are on display at aquariums worldwide. In Japan jellyfish are kept as pets in special aquariums.

Species accounts

List of Species

Thimble jelly

Linuche unguiculata

order

Coronatae

family

Linuchidae

taxonomy

Linuche unguiculata Schwartz, 1788, American Tropical Atlantic.

other common names

None known.

physical characteristics

The medusae grow only to 1 in (2.5 cm) in height. As the name implies, they are thimble-shaped, with a shallow groove near the top of the bell. They have eight very short tentacles and eight rhopalia alternating between the 16 lappets at the bell margin. The outside of the bell is transparent, with numerous warts of stinging cells. The inner part of the bell is white with greenish brown spots. The polyps form colonies and are covered by a thin, chitinous sheath.

distribution

This species lives in tropical and subtropical waters worldwide.

habitat

The medusae occur near the surface in near shore waters in spring and summer, which is unusual for coronate species. Polyps occur on coral rubble.

behavior

The thimble jelly usually is found in large groups, up to 0.6 mi² (1 km²) in area, just beneath the surface. They are very active swimmers, moving horizontally in circles. Surface convection cells cause them to become concentrated, and their swimming behavior helps them remain in an aggregation.

feeding ecology and diet

The medusae catch a variety of zooplankton prey on the lappets. The colored spots in the bell are filled with intracellular algae (zooxanthellae) that transfer some of their photosynthesized carbon to the medusa, contributing to the animal's nutrition.

reproductive biology

The fertilized eggs of the thimble jelly form large larvae that remain planktonic for three to four weeks. They settle and form an unbranched colony of polyps. Each polyp can produce an unusually large number (up to 40) of ephyrae that grow into sexually mature medusae.

conservation status

Not listed by the IUCN.

significance to humans

Stings from the planktonic larvae or medusae of the thimble jelly cause the syndrome called "seabathers' eruption." The problem is aggravated when they become trapped underneath a swimsuit. This syndrome, characterized by a prickling sensation and red bumps persisting for 7–12 days, is an irritating but not a dangerous condition.

Crown jellyfish

Periphylla periphylla

order

Coronatae

family

Periphyllidae

taxonomy

Periphylla periphylla Peron and Lesueur, 1809, equatorial Atlantic Ocean.

other common names

None known.

physical characteristics

These medusae have a conical swimming bell that is up to 8 in (20 cm) tall and 6.5 in (17 cm) in diameter, but specimens from oceanic waters usually are less than 2 in (5 cm) in size. The bell of small specimens is transparent and reveals the reddish brown stomach. In large specimens, the bell is opaque and maroon in color. The bell has a pronounced groove with 16 deeply notched lappets beneath it. Twelve thick tentacles emerge from the bell surface above the clefts, in a repeating pattern of three tentacles and one rhopalium. The stomach is baglike. Oral arms and the polyp stage are lacking.

distribution

This species is found at mesopelagic depths in all oceans worldwide. Populations that are several orders of magnitude greater than they are in the open ocean have been found in Norwegian fjords, especially Lurefjorden.

habitat

The crown jellyfish generally is found at depths below 3,000 ft (900 m), where water temperatures remain a cool 45°F (7°C) or less all year. At high latitudes they inhabit shallower depths, 650–1,300 ft (200–400 m) in the daytime and from the surface to 650 ft (200 m) at night.

behavior

These medusae undergo vertical migration from deepwater in the daytime to shallower depths at night, presumably following their prey. Exposure to white light causes rapid downward swimming. As with other deep-dwelling coronate medusae, when they are disturbed, the bell and ovaries are brilliantly bioluminescent. They also produce copious amounts of luminescent mucus that contains stinging cells.

feeding ecology and diet

The natural behavior of medusae was observed with red light and video cameras on a Remotely Operated Vehicle (ROV) in Lurefjorden, Norway. The medusae hold their tentacles up alongside the bell or at right angles to the bell. They swim downward for about 30 ft (10 m) and then drift upward. The tentacles sometimes quickly arch toward the mouth, coil, and enter the stomach. Few prey (copepods, ostracods, and chaetognaths) were found in ROV-collected specimens. These

medusae have low metabolic rates and apparently survive on few (less than 35) prey items daily.

reproductive biology

Fertilized eggs are released in deepwater, where they drift, not feeding for several months. Eggs and larvae are present all year in Lurefjorden, suggesting lack of seasonality in the relatively constant environment of the deep ocean. The larvae develop directly into medusae without polyp or ephyra stages.

conservation status

Not listed by the IUCN.

significance to humans

In Lurefjorden the crown jellyfish may have nearly excluded small fish, which are common in other fjords. There are possible medical applications for the bioluminescent proteins. Deep oceanic populations have no apparent significance for humans.

Upside-down jellyfish

Cassiopea xamachana

order

Rhizostomeae

family

Cassiopeidae

taxonomy

Cassiopea xamachana R. P. Bigelow, 1892, Jamaica, West Indies.

other common names

None known.

physical characteristics

Medusae in the genus Cassiopea are unique in resting bell side down on the ocean bottom. The swimming bell may reach 6 in (15 cm) in diameter. It is flattened, with 40 lappets. The oral arms are about 1.5 times the bell radius. They branch laterally and have numerous tiny tentacle-like projections. The upside-down medusae appear to be clumps of algae because of the bushy greenish brown oral arms that cover the bell. The topside of the bell can be marked boldly with regular spots and stripes in brown and blue. Tentacles are lacking.

distribution

This species is found in the eastern tropical Atlantic, including Florida, the Caribbean, and Mexico. Other members of the genus occur in tropical waters worldwide.

habitat

These jellyfish are found year-round in sunny, shallow tropical lagoons and mangroves and in coral back-reef areas.

behavior

Although the medusae rest bell side down on the bottom, regular swimming pulsations are important in terms of feeding and water exchange for respiration. The medusae do not swim in the water column unless they are disturbed.

feeding ecology and diet

Nutrition of the upside-down jellyfish depends on a combination of zooplankton feeding and symbiosis with intracellular algae (zooxanthellae). Pulsations of the bell sweep small epibenthic crustaceans and zooplankton into the oral arms, where they are caught by the numerous tiny tentacle-like projections and passed to the many small mouths along the oral arms. The greenish brown color of the oral arms comes from the zooxanthellae in the tissues. These algae contribute photosynthetic products to the medusa's nutrition. The symbiosis represents a mutual exchange of nutrients that, together with zooplankton, supports algae and medusa metabolism, growth, and reproduction. The polyps also contain zooxanthellae and feed on small crustaceans.

reproductive biology

The life cycle is typical of rhizostome scyphozoans. Metamorphosis of the larvae into polyps requires a peptide derived from the cell walls of decomposing plants, such as mangroves. Polyps can reproduce asexually by budding off chains of special individuals that settle to form polyps. Strobilation produces only one ephyra per polyp.

conservation status

Not listed by the IUCN.

significance to humans

The creation of protected lagoons for resorts or aquaculture and associated eutrophication (nutrient pollution) of those areas have resulted in increased medusa populations in the Florida Keys and Mexico. The medusae are harmless to humans but can be irritating if they are handled.

Golden jellyfish

Mastigias papua

order

Rhizostomeae

family

Mastigiidae

taxonomy

Mastigias papua Lesson, 1830, Japan.

other common names

None known.

physical characteristics

The firm bell is hemispherical and up to 3.5 in (9 cm) in diameter. The bell is translucent with white spots and a granular appearance. The eight oral arms are frilled and flare near the bell, tapering to smooth clublike structures at the end. Tissue along the bell margin and in the frilly oral arms is golden in color, from intracellular algae (zooxanthellae). Tentacles are lacking.

distribution

This species is found in the tropical southern and central Pacific Ocean and into the Indian Ocean, Malaysia, Japan, Fiji, the Philippines, and Palau.

habitat

Medusae occur in tropical surface waters near shore. They have tremendous populations in the marine lakes of Palau.

behavior

These medusae undergo daily horizontal migrations across the lakes of Palau, staying in the sun or avoiding the shade, which maximizes photosynthesis by their symbiotic algae. The medusae also migrate vertically at night down to nutrient-rich deeper layers in the lakes, which provide nutrients for algal photosynthesis.

feeding ecology and diet

The medusae have symbiotic algae (zooxanthellae) in the tissues that supply much of their nutrition. They also eat zooplankton, catching them with small tentacle-like projections on the oral arms. The polyps also have zooxanthellae and eat zooplankton.

reproductive biology

The medusa (sexual) and polyp (asexual) generations alternate, as is typical of rhizostome medusae. In the marine lakes in Palau, asexual reproduction can occur all year, but medusa production (strobilation) is inhibited at high temperatures that kill the zooxanthellae.

conservation status

Not listed by the IUCN.

significance to humans

The very large populations of medusae (1.5 million) in marine lakes have become an important tourist attraction in Palau. The jellyfish in the lakes also have been featured in National Geographic and an IMAX film.

Cannonball jellyfish

Stomolophus meleagris

order

Rhizostomeae

family

Stomolophidae

taxonomy

Stomolophus meleagris L. Agassiz, 1862, Atlantic Ocean, East Coast of United States.

other common names

English: Cabbagehead jellyfish.

physical characteristics

The firm, almost spherical swimming bell grows up to 7 in (18 cm) in diameter and lacks tentacles. The oral arms are fused to form a rigid, short mound below the bell. The bell color ranges from nearly white to bluish, and it may darken to reddish orange with blue speckles toward the bell margin; the oral arms are white.

distribution

The cannonball jellyfish occurs in subtropical and tropical Atlantic and Pacific North American waters. It is abundant from North Carolina through the Gulf of Mexico. It also is found in

the Caribbean, in South America to northern Argentina, and in the Pacific from southern California to Ecuador.

habitat

The medusae are found in coastal waters in summer.

behavior

These medusae are strong swimmers. Within a group, individuals swim horizontally in the same direction, oriented with or against the wind and surface-wave or current direction.

feeding ecology and diet

The medusae lack obvious long feeding tentacles and oral arms, but they pump water containing zooplankton through the oral arms and elaborate filtering structures within the bell. There, minute tentacle-like projections with nematocysts catch prey. The medusae eat a variety of zooplankton prey, including mollusk veligers, copepods, tintinnids, larvaceans (= appendicularians), and fish eggs.

reproductive biology

This species exhibits the typical life cycle of rhizostome scyphozoans, having both medusa (sexual) and polyp (asexual) stages. Only one or two ephyrae are produced per polyp.

conservation status

Not listed by the IUCN.

significance to humans

This is one of the 11 species of rhizostome medusae that are fished commercially for human consumption. This species has no stinging tentacles but produces mucus that is shed in strings laden with nematocysts that irritate skin on contact. They also act as a host for juvenile butterfish Peprilis species that depend on the jellyfish for protection.

Lion's mane jellyfish

Cyanea capillata

order

Semaeostomeae

family

Cyaneidae

taxonomy

Cyanea capillata Linnaeus, 1758, North Sea.

other common names

None known.

physical characteristics

Medusae are reported to grow to 80 in (2 m) in diameter but are usually less than an eighth that size. The edge of the swimming bell is divided into eight lobes, giving it the appearance of a flower viewed from above. As many as 150 long tentacles are present in groups beneath each of the eight lobes. The oral arms form a diaphanous mass beneath the bell that is a little longer than it is wide. The bell often is brownish orange, and the oral arms are maroon, but color varies from pale yellow to dark red.

distribution

Medusae are present during summertime in boreal latitudes, but in wintertime they occur in temperate zones. Reported from Arctic, northern European, North American Atlantic and Pacific, southern Australian, and Antarctic waters.

habitat

The medusae prefer cool temperatures below 70°F (20°C). They often are found in surface waters of estuaries or coastal bays.

behavior

The swimming bell of the medusa orients upward toward the water surface. The swimming beat is slow, just maintaining the position of the medusa in the water column. The tentacles may spread out several meters around the bell. They do not form aggregations.

feeding ecology and diet

The diet includes planktonic crustaceans, such as copepods and cladocerans, and fish eggs and larvae. It also contains large proportions of pelagic tunicates (larvaceans = appendicularians), ctenophores (comb jellies), hydromedusae, and scyphomedusae. The long tentacles snare such relatively large prey and bring them to the oral arms, where they are enveloped and digested. Predation effects have been studied in Australia, Norway, and Alaska, where populations of medusae remove only a small percentage of the zooplankton daily.

reproductive biology

The life cycle is typical of semaeostome scyphomedusae. Sperm are shed into the water and fertilize eggs in the female. Larvae are brooded along the edges of the oral arms. Sexual reproduction takes place near the end of the life of the medusa, in early spring in warm climates and during the summer at high latitudes. Larvae attach to the undersides of hard surfaces and form polyps, which asexually produce medusae and other polyps.

conservation status

Not listed by the IUCN.

significance to humans

Medusae have a painful sting that annoys swimmers and fishermen retrieving fishing nets.

Sea nettle

Chrysaora quinquecirrha

order

Semaeostomeae

family

Pelagiidae

taxonomy

Chrysaora quinquecirrha Desor, 1848, Nantucket Bay, Massachusetts, United States.

other common names

None known.

physical characteristics

The swimming bell may reach 10 in (25 cm) in diameter, but medusae generally are much smaller. The edges of the swimming bell appear scalloped, with 16 or more lappets. One large tentacle emerges from between every other lappet, and twice as many small tentacles arise from beneath the lappets. Eight rhopalia are present in alternate clefts between lappets. The narrow oral arms are long and diaphanous. Medusa color ranges from milky white to white with radiating purplish red stripes on the bell.

distribution

This species is found near shore in temperate to subtropical Atlantic Ocean waters of North, Central, and South America above the equator and in the Gulf of Guinea and Angola, Africa. They also are reported from the western Pacific Ocean in the Philippines, southern China, Malaysia, and the Bay of Bengal.

habitat

Medusae are most abundant during the summer in estuaries, where they thrive at salinity levels as low as 7 ppt. In Chesapeake Bay unusually low salinity levels in spring result in fewer medusae, with the distribution shifted to waters of higher salinity.

behavior

The medusae swim constantly in slow circles, owing to the drag of their oral arms and tentacles. As seems to be true for other scyphomedusa species, the sea nettle feeds continuously.

feeding ecology and diet

This species has been studied extensively in Chesapeake Bay and its tributaries, where it occurs in great numbers. When they are abundant, medusae may reduce copepod populations. This species also feeds on comb jellies (Mnemiopsis leidyi) and can eliminate them from tributaries. Bay anchovy (Anchoa mitchilli) spawns during peak medusa abundance, and medusae may eat 50% of the fish eggs and larvae daily, on average. Surprisingly, the polyps eat and digest oyster larvae (veligers), but the medusae do not digest them.

reproductive biology

The life cycle is typical of semaeostome scyphomedusae, having both a polyp and a medusa stage. In temperate Chesapeake Bay, the polyps become dormant during the cold winter months. They excyst and undergo strobilation in spring when water temperatures exceed 60°F (17°C). More ephyrae are produced at salinity levels between 10 and 25 ppt than at lower or higher salinity levels. Spawning takes place around dawn. Larvae are not brooded by the females.

conservation status

Not listed by the IUCN.

significance to humans

This species was so abundant in Chesapeake Bay during the 1960s that a legislative bill was passed to provide money for research on it. The medusae have an irritating sting, which deters swimming, especially in the shallow tributaries where they are most abundant. The species may be of overall benefit in the food web, by controlling populations of comb jellies, which consume oyster veligers and much more zooplankton than do the medusae. Thus, more zooplankton may be available for zooplanktivorous fishes, such as bay anchovy, which are prey for favorite sport fish, such as striped bass and bluefish.

Nightlight jellyfish

Pelagia noctiluca

order

Semaeostomeae

family

Pelagiidae

taxonomy

Pelagia noctiluca Forskål, 1775, Mediterranean Sea.

other common names

English: Mauve baubler.

physical characteristics

The swimming bell usually is less than 3.5 in (9 cm) in diameter. It has a bumpy surface from clusters of stinging cells, which impart a purple or yellowish color to the translucent bell. There are four elongate oral arms and eight long tentacles that alternate with eight rhopalia in the clefts between lappets. There is no polyp stage.

distribution

The medusa is found in tropical to warm temperate Atlantic and Pacific waters and in the Mediterranean Sea. They are present throughout the year in warm waters.

habitat

They are found in surface waters of the open ocean, but sometimes can be advected into shallow coastal waters.

behavior

This species is unusual among semaeostome scyphomedusae in being bioluminescent. Medusae emit a blue-green light when they are touched or injured. Mucus released from the damaged area continues to glow. The bioluminescence is believed to serve a protective function. Medusae look like glowing balls at night in a boat's wake.

feeding ecology and diet

This species has a diverse diet that includes all types of zooplankton, such as crustaceans, mollusk larvae, chaetognaths, pelagic tunicates (larvaceans, salps, and doliolids), siphonophores, hydromedusae, ctenophores, and fish eggs and larvae. It feeds in the same manner as other semaeostome scyphomedusae. Populations of medusae may require a 5–8% diet of zooplankton daily to balance their metabolism.

reproductive biology

This species is unusual among semaeostome scyphomedusae in lacking a polyp stage. The larvae develop directly into ephyrae, without ever settling on the bottom. Medusae reproduce throughout the year in tropical waters.

conservation status

Not listed by the IUCN.

significance to humans

The nightlight jellyfish periodically develops large populations in the Mediterranean Sea. The medusae can become concentrated near the shore in crowded tourist areas. They have a painful sting, which can cause a severe reaction and has led to two international scientific conferences on jellyfish blooms in the Mediterranean Sea. Dramatic fluctuations in their abundance in the Mediterranean is linked to 12-year climate cycles.

Moon jelly

Aurelia aurita

order

Semaeostomeae

family

Ulmaridae

taxonomy

Aurelia aurita Linnaeus, 1758, Baltic Sea.

other common names

None known.

physical characteristics

The diameter of the medusa swimming bell may reach 20 in (50 cm). The eight lobes of the bell are marked by shallow indentations, each with a rhopalium. The bell is translucent, usually with a pink tinge. The gonads resemble a pink four-leaf clover, as seen inside the semitransparent bell. Hundreds of short, fine tentacles hang in a single circle from the bell margin. The oral arms extend only to about the edge of the bell and may have bright reddish orange larvae brooded in pockets at the edges. Polyps are white and about 0.1–0.2 in (2–4 mm) long, with a single ring of tentacles. They often occur in large aggregations. Developing ephyrae are orange.

distribution

The moon jelly is reported from all oceans, from tropical to temperate waters between 70°N and 55°S latitude. They are common in coastal European, North American, and Japanese waters. They also are reported from some locations in Asia, Australia, Pacific Islands, South America, and Africa. This species may be endemic to Europe and introduced elsewhere. It closely resembles other species in the genus. Recent molecular studies indicate perhaps six species in the genus that may be easily confused.

habitat

This species occurs in a wide range of conditions, in waters with near-freezing winter temperatures, to 90°F (32°C), and with salinity levels of 14–38 ppt. Medusae generally are present only in warm months in temperate locations, but they occur throughout the year in tropical and some temperate locations. They often are found in estuaries, fjords, and bays, usually at the surface to 100 ft (30 m). Large populations may form in semi-enclosed bays with restricted tidal exchange. The polyps are found at depths above 65 ft (20 m) on the undersides of hard structures.

behavior

The moon jelly is remarkable in forming large aggregations of medusae. Aggregations may be a mile or more (2 km) in length and can contain millions of individuals. These groups may be seen from low-flying airplanes and detected by "fish finders" on fishing boats. The aggregations are formed because of the tendency of the medusae to swim either up or down against directional water flow. They also are reported to swim horizontally by orienting to a specific compass direction in sunlight, causing them to gather in certain locations.

feeding ecology and diet

The fine tentacles of the medusae catch mainly small crustacean zooplankton, such as copepods and cladocerans. They also feed on fish and mollusk larvae, small hydromedusae, and even microzooplankton, such as ciliates. They may catch food in the mucus on the outer surface of the swimming bell.

reproductive biology

The life cycle is typical of semaeostome scyphomedusae, having both a medusa (sexual) stage and a polyp (asexual) stage. Moon jelly aggregations are believed to increase fertilization success by bringing females and males into proximity. The males release sperm strands into the water, which are taken up by the females during feeding. The fertilized eggs form larvae that are brooded in pockets on the oral arms. The larvae attach to hard surfaces and become polyps, which then bud medusae.

conservation status

Not listed by the IUCN.

significance to humans

Aggregations sometimes have clogged the seawater intakes of power plants in Asia. The medusae also may reduce commercial herring populations by feeding on larvae in Kiel Bight, Germany. Their sting is not painful to humans. They are raised easily for aquarium exhibits and sometimes are kept in special home aquariums.

Stalked jellyfish

Haliclystus auricula

order

Stauromeduasae

family

Lucernariidae

taxonomy

Haliclystus auricula Rathke, 1806, Norway.

other common names

None known.

physical characteristics

In the Stauromedusae the medusa is stalked and remains attached to the substrate. The "bell" (calyx) is funnel-shaped and grows to 1.25 in (3 cm) in diameter, with the mouth at the bottom of the funnel. The calyx has eight arms, with clusters of 30–80 knobbed tentacles at the tips. Between the arms are eight bean-shaped sticky pads. The stalk is as long as the calyx is wide. The color of this jellyfish often matches the substrate—green, brown, yellow, or reddish-purple.

distribution

This species is found on the northern Atlantic and Pacific coasts above 40°N latitude.

habitat

These stauromedusae live attached to rock, algae, or eelgrass in shallow intertidal and subtidal areas late spring through autumn.

behavior

Stauromedusae can move about by somersaulting. The stalk bends toward the substrate, where the calyx can attach temporarily by a sticky pad between the arms or by the tentacles. The stalk releases its hold, arches over, and reattaches to the substrate in a different location as the calyx releases its attachment.

feeding ecology and diet

Stauromedusae feed on epibenthic animals, including amphipods, copepods, and gastropods, that bump into their stinging tentacles. The arms bend toward the center to bring captured prey to the central mouth.

reproductive biology

The stalked jellyfish spawns into the water at first daylight. Fertilized eggs form creeping, nonswimming larvae. When the larvae attach to the substrate, they form a minute polyp, which grows directly into an adult.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Arai, Mary N. A Functional Biology of Scyphozoa. London:Chapman and Hall, 1997.

Cornelius, Paul F. S. "Keys to the Genera of Cubomedusae and Scyphomedusae (Cnidaria)." In Proceedings of the Sixth International Conference on Coelenterate Biology, edited. by J. C. Den Hartog. Leiden, The Netherlands: National Natuurhistorich Museum, 1997.

Franc, André. "Classe des Scyphozoaires." In Traité de Zoologie: Anatomie, Systématique, Biologie. Vol. 3, Cnidaires, Cténaires, edited by Pierre-P. Grassé. Paris: Masson, 1993.

Mayer, A. G. Medusae of the World. Vol. 3, The Scyphomedusae. Washington, DC: Carnegie Institution, 1910.

Mianzan, Hermes W., and Paul F. S. Cornelius. "Cubomedusae and Scyphomedusae." In South Atlantic Zooplankton, edited by Demetrio Boltovskoy. Leiden, The Netherlands: Backhuys, 1999.

Purcell, Jennifer E., W. Monty Graham, and Henri J. Dumont. Jellyfish Blooms: Ecological and Societal Importance. Developments in Hydrobiology, no. 155. Dordrecht, The Netherlands: Kluwer Academic, 2001.

Purcell, Jennifer E., Alenka Malej, and Adam Benovic. "Potential Links of Jellyfish to Eutrophication and Fisheries." In Ecosystems at the Land-Sea Margin: Drainage Basin to Coastal Sea, edited by Thomas C. Malone, Alenka Malej, Larry W. Harding Jr., Nenad Smodlaka, and R. Eugene Turner. Washington, DC: American Geophysical Union, 1999.

Wrobel, David, and Claudia Mills. Pacific Coast Pelagic Invertebrates: A Guide to the Common Gelatinous Animals. Monterey, CA: Monterey Bay Aquarium, 1998.

Periodicals

Brodeur, Richard D., Claudia E. Mills, James E. Overland, Gary E. Walters, and James D. Schumacher. "Evidence for a Substantial Increase in Gelatinous Zooplankton in the Bering Sea, with Possible Links to Climate Change." Fisheries Oceanography 8, no. 4 (1999): 296–306.

Kramp, P. L. "A Synopsis of the Medusae of the World." Journal of the Marine Biological Association of the United Kingdom 40 (1961): 1–469.

Larson, Ronald J. "Feeding in Coronate Medusae (Class Scyphozoa, Order Coronatae)." Marine Behavior and Physiology 6 (1979): 123–129.

——. "Scyphomedusae and Cubomedusae from the Eastern Pacific." Bulletin of Marine Science 47 (1990): 546–556.

——. "Diet, Prey Selection and Daily Ration of Stomolophus meleagris, a Filter-Feeding Scyphomedusa from the NE Gulf of Mexico." Estuarine Coastal and Shelf Science 32 (1991): 511–525.

——. "Riding Langmuir Circulations and Swimming in Circles: A Novel Clustering Behavior by the Scyphomedusa Linuche unguiculata." Marine Biology 112 (1992): 229–235.

Mills, Claudia E. "Jellyfish Blooms: Are Populations Increasing Globally in Response to Changing Ocean Conditions?" Hydrobiologia 451 (2001): 55–68.

Purcell, Jennifer E. "Predation on Zooplankton by Large Jellyfish (Aurelia labiata, Cyanea capillata, Aequorea aequorea) in Prince William Sound, Alaska, USA." Marine Ecology Progress Series 246 (2003): 137–152.

Purcell, Jennifer E., and Mary N. Arai. "Interactions of Pelagic Cnidarians and Ctenophores with Fishes: A Review." Hydrobiologia 451 (2001): 27–44.

Other

Gershwin, Lisa. "Medusozoa Home Page." [June 13, 2003]. <http://www.medusozoa.com>.

Jellies and Other Ocean Drifters. Video. Monterey Bay Aquarium, 1996.

"The Jellies Zone." [June 13, 2003]. <http://jellieszone.com>.

Ocean Drifters. Video. National Geographic Explorer, 1993.

Mills, Claudia E. Home Page. June 10, 2003 [June 13, 2003]. <http://faculty.washington.edu/cemills>.

Monterey Bay Aquarium. [June 13, 2003]. <http://mbayaq.org>.

The Shape of Life: Life on the Move: Cnidarians. Video. Sea Studios, Monterey, CA, 2001.

Jennifer E. Purcell, PhD