Pelagia noctiluca

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Geographic Range

Found in the Mediterranean and the Atlantic Ocean, it lives mainly in the open ocean as well as in coastal waters. (Grzimek 1972)

Habitat

The habitat is primarily pelagic, or in the open ocean. However, this species can survive almost anywhere ocean currents carry it, including benthic and temperate coastal habitats. (Calder 2000;Grzimek 1972)

Physical Description

Like other Cnidarians, this species is radially symmetrical. They have distinct tissues, but no organs, and only one body opening. The tissues are the outer epidermis, the inner gastrodermis, and a middle layer of gelatinous mesoglea, which has a cartilege-like consistency. The medusa stage is most prominant, and no bottom-dwelling stage exists. The umbrella edge is divided into eight lobes, where sense organs such as light receptors and odor pits are located. The umbrella can be bell-shaped or hemispherical, and color can range from purple to brownish-red. Pelagia noctiluca has a frilled edge on the bell, with eight thin, stinging tentacles and four lobes hanging down from the mouth, called oral arms. The tentacles are very elastic. The name means "night light" in German for a reason. Very colorful, this jellyfish phosphoresces when disturbed and can leave a luminous mucous behind if handled. It is called the "mauve jelly" by the British. Also known as the oceanic jelly, this species is adapted to life in the open water. It is in the class Scyphozoa, the true jellyfish. The estimated lifespan of Pelagia noctiluca is two to six months, and death is usually caused by rough waters. (Grzimek 1972; Stachowitsch 1991;Calder 2000; Marr 1999)

Reproduction

The adults, which have separate sexes, reproduce sexually by releasing gametes from gonads located near the center of the body. The ova and sperm are released through the mouth of the jellyfish, and fertilize externally. Each fertilized egg forms a planulae, an undifferentiated mass of cells that swims with external cilia. Planula may be widely dispersed by oceanic currents. Unlike other species which have a bottom-dwelling polyp stage, Pelagia noctiluca's planulae develop directly into ephyrae, young medusae. The ephyrae quickly grows into an adult medusa, completing the life cycle. (Banister and Campbell 1985; Stachowitsch 1991;Calder 2000)

  • Parental Investment
  • no parental involvement

Behavior

Jellyfish sometimes form shoals, or large groups. Pelagia noctiluca has appeared in shoals 45 kilometers in length, with thousands of jellyfish involved. They move by rhythmically contracting a muscular ring on the bottom of the bell, which propels them. The ring is formed by many specialized epithelial cells that can each contract individualy as well. The mesoglea can aid in buoyancy by expelling certain ions, which are replaced by lighter ones. However, the jellyfish usually end up wherever the currents take them.

Pelagia noctiluca defends itself with the same nematocysts used to capture prey. The nematocysts are "fired" by using water pressure. First, a high concentration of ions is built up inside the cells. When the nematocyst is stimulated to discharge, the walls become permeable to water. The water rushing in shoves the barb out and into the other organism, injecting a toxin along the way. This is one of the fastest cellular processes known in nature. (Banister and Campbell 1985;Grzimek 1972;Raven and Johnson 1999)

Food Habits

Carnivorous like other Cnidarians, this species preys mainly on zooplankton, small fish, crustaceans, other jellyfish, and eggs. Pelagia noctiluca captures its prey with tentacles armed with cnidocytes, each of which contains a nematocyst. Nematocysts have barbed filaments to trap their prey and toxins to stun them. They can even pierce the shell of a crab with their barbs. Food is digested intracellularly as well as extracellularly, in a gut cavity, enabling them to eat multicellular animals. (Raven and Johnson 1999; Banister and Campbell 1985)

Economic Importance for Humans: Positive

Pelagia noctiluca are beautiful, especially when they phosphoresce. The chemical reactions causing their luminescence are currently of great interest to researchers. Other jellyfish are used for medical and therapeutic purposes, and Pelagia noctiluca might soon be helpful for humans. One possible use of their fluorescent protein is as a genetic marker to detect protein movement or gene expression in research in developmental, environmental and medical biology. (Manning 1997)

Economic Importance for Humans: Negative

-Pelagia noctiluca- is among the jellyfish that scare tourists away from beaches, especially in the Mediterranean. Italian beaches were overrun by large groups of them in the summer of 1999. The sting of -Pelagia noctiluca- is venomous to humans, but normally only causes a whip-like scar across the body. In rare cases of allergic reactions, life-threatening conditions like anaphylactic shock can occur. Fishermen are also affected by jellyfish, including -Pelagia noctiluca- . There have been reports from France of jellyfish tearing holes in fishing nets. (Marr 1999;Calder 2000)

Conservation Status

-Pelagia noctiluca- is not in danger of extinction at the present time. They are multiplying in number in the Mediterranean, but are expected to return to normal levels in the next few years. (Marr 1999)

Contributors

Erin Leverenz (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

References

Banister, D., D. Campbell eds.. 1985. Sea Anemones and Jellyfishes. Pp. 176-177 in The Encyclopedia of Aquatic Life. New York: Fact on File Publications.

Calder, .. "Keys to Marine Invertebrates of the Woods Hole Region" (On-line). Accessed February 6, 2000 at http://www.mbl.edu/html/KEYS/INVERTS/3/Dscyphozoakeys.htm.

Grzimek, D. 1972. Coelentrates. Pp. 209-215 in Grzimek's Animal Life Encyclopedia Volume 1 Lower Animals. New York: Van Nostrand and Reinhold Company.

Manning, E. March 1997. Glow Fish. BioScience, Vol 47: 135-8.

Marr, M. August 23, 1999. "Electronic Library (members only) 'Italy smarts from invasion of the jellyfish'" (On-line). Accessed February 2, 2000 at http://www.elibrary.com/.

Raven, .., .. Johnson. 1999. Biology. Boston: McGraw-Hill.

Stachowitsch, .. 1991. The Invertebrates: An Illustrated Glossary. New York: Wiley-Liss.