jellyfish, common name for the free-swimming stage (see polyp and medusa polyp and medusa, names for the two body forms, one nonmotile and one typically free swimming, found in the aquatic invertebrate phylum Cnidaria (the coelenterates).
..... Click the link for more information. ), of certain invertebrate animals of the phylum Cnidaria Cnidaria (nīdâr`ēə) or Coelenterata
..... Click the link for more information. (the coelenterates). The body of a jellyfish is shaped like a bell or umbrella, with a clear, jellylike material filling most of the space between the upper and lower surfaces. A mouth is located in the center of the undersurface and tentacles dangle from the bell margin. Many jellyfish are colored, with pink or orange internal structures visible through the colorless or delicately tinted bell, and all are exquisitely designed; they are among the most beautiful of animal types. Typically, jellyfish catch their prey with the aid of stinging cells located in the tentacles; many jellyfish can cause irritating or even dangerous stings to humans. Food is carried by the tentacles to the mouth, then is moved into the stomach and is distributed to the body through radial canals. Jellyfish move up and down by contracting and relaxing the bell, using muscles that circle the bell margin; they are carried horizontally by waves and currents. Jellyfish of the class Hydrozoa are small, ranging from 1-8 in. (0.32 cm) to several inches in diameter, and usually have four tentacles. They have several (often four) unbranched radial canals and simple sense organs. In this group the polyp, or attached stage, is often larger and more conspicuous than the medusa. Jellyfish of the class Scyphozoa, sometimes called true jellyfish, are larger and often have numerous tentacles; they have branched radial canals and complex sense organs. In this group the medusa is the prominent form and the polyp is reduced to a small larval stage. Scyphozoan jellyfish are commonly 3-4 in. to 16 in. (2–40 cm) in diameter; Aurelia, the flattened jellyfish common along North American coasts, may be as much as 1 ft (30 cm) across. One species of Cyanea found in cold northern seas may reach 6 ft (1.8 m) across and have tentacles over 100 ft (30 m) long. Tiny Craspedacusta, a hydrozoan jellyfish less than 1 in. (2.5 cm) long, occurs in freshwater lakes and ponds, but all other jellyfish are marine, living in ocean depths as well as along the coasts. The hydrozoan Physalia, or Portuguese man-of-war, is actually a large colony of modified individuals, some medusalike and some polyplike; a large gas-filled sac acts as a float for the colony. The tentacles of such a colony may extend 60 ft (18 m) into the water and can cause severe injuries to swimmers. Physalia is usually bright blue, sometimes with tints of pink and orange. The purple sail, Velella, a floating colony 1 to 3 in. (2.5–7.5 cm) across, may be blue or purple. Jellyfish are classified in the phylum Cnidaria, classes Hydrozoa and Scyphozoa.
Any of about 200 described species of free-swimming marine cnidarians (in the classes Scyphozoa and Cubozoa), many of which have a bell-shaped body. The term is also frequently applied to other similar cnidarians (e.g., Portuguese man-of-war) and some unrelated forms (e.g., ctenophores and salps). In scyphozoan jellyfish, the free-swimming medusa form is the dominant stage, with the sessile polyp form found only during larval development. Jellyfish live in all oceans and include the familiar disk-shaped animals that are often found drifting along the shoreline. Most species are 1–16 in. (2–40 cm) in diameter; some are 6 ft (1.8 m) in diameter, with tentacles more than 100 feet (30 m) long. Though some jellyfish simply filter-feed, most feed on small animals (e.g., crustaceans) that they catch in their tentacles, whose stinging cells immobilize the prey; contact can be irritating and sometimes dangerous to humans. The cubozoan jellyfish comprise 50 species of box jellies (the rather spherical body is squared off at the edges), which are usually 1–2 in. (2–4 cm) in diameter.
jellyfish
..... Click the link for more information. ), of certain invertebrate animals of the phylum Cnidaria Cnidaria (nīdâr`ēə) or Coelenterata
..... Click the link for more information. (the coelenterates). The body of a jellyfish is shaped like a bell or umbrella, with a clear, jellylike material filling most of the space between the upper and lower surfaces. A mouth is located in the center of the undersurface and tentacles dangle from the bell margin. Many jellyfish are colored, with pink or orange internal structures visible through the colorless or delicately tinted bell, and all are exquisitely designed; they are among the most beautiful of animal types. Typically, jellyfish catch their prey with the aid of stinging cells located in the tentacles; many jellyfish can cause irritating or even dangerous stings to humans. Food is carried by the tentacles to the mouth, then is moved into the stomach and is distributed to the body through radial canals. Jellyfish move up and down by contracting and relaxing the bell, using muscles that circle the bell margin; they are carried horizontally by waves and currents. Jellyfish of the class Hydrozoa are small, ranging from 1-8 in. (0.32 cm) to several inches in diameter, and usually have four tentacles. They have several (often four) unbranched radial canals and simple sense organs. In this group the polyp, or attached stage, is often larger and more conspicuous than the medusa. Jellyfish of the class Scyphozoa, sometimes called true jellyfish, are larger and often have numerous tentacles; they have branched radial canals and complex sense organs. In this group the medusa is the prominent form and the polyp is reduced to a small larval stage. Scyphozoan jellyfish are commonly 3-4 in. to 16 in. (2–40 cm) in diameter; Aurelia, the flattened jellyfish common along North American coasts, may be as much as 1 ft (30 cm) across. One species of Cyanea found in cold northern seas may reach 6 ft (1.8 m) across and have tentacles over 100 ft (30 m) long. Tiny Craspedacusta, a hydrozoan jellyfish less than 1 in. (2.5 cm) long, occurs in freshwater lakes and ponds, but all other jellyfish are marine, living in ocean depths as well as along the coasts. The hydrozoan Physalia, or Portuguese man-of-war, is actually a large colony of modified individuals, some medusalike and some polyplike; a large gas-filled sac acts as a float for the colony. The tentacles of such a colony may extend 60 ft (18 m) into the water and can cause severe injuries to swimmers. Physalia is usually bright blue, sometimes with tints of pink and orange. The purple sail, Velella, a floating colony 1 to 3 in. (2.5–7.5 cm) across, may be blue or purple. Jellyfish are classified in the phylum Cnidaria, classes Hydrozoa and Scyphozoa.
jellyfish
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Life cycle of the common jellyfish Aurelia. Eggs released by females pass out through the …
(credit: © Merriam-Webster Inc.)
jellyfish
1. any marine medusoid coelenterate of the class Scyphozoa, having a gelatinous umbrella-shaped body with trailing tentacles
2. any other medusoid coelenterate
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