Marine Phyla Pages -- Coastal Carolina University
SCYPHOZOA
Scyphozoa
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Systematics
Jellyfish range in size from a mere twelve millimeters to more than two meters across. The largest is Cyanea arctica, which may have tentacles over 40m long! Despite their often enormous size, jellyfish have no head, no skeleton, and no special organs for respiration or excretion. Their life cycle involves an alternation between sesslie polyp phase and a free-swimming medusa stage, though the medusa stage usually predominates.
Feeding
Food and waste must be passed in and out through the same opening, since like other cnidarians, they have no digestive tract. Cilia within the digestive cavity move water and dissolved food and gases around. While smaller jellyfish may feed on trapped food particles from the water, the larger jellyfish are predators on fish or on swimming invertebrates. They accomplish this by using special stinging cells to immobilize their prey.
Habitat & Locomotion
Most scyphozoan jellyfish are pelagic, free-swimming forms of the open ocean. Some small species are planktonic, and one order, the Stauromedusae, are sessile on the ocean floor. All scyphozoa are marine, though a few fresh water forms have occasionally been reported.
Defense
True jellyfish [can be] deadly creatures. Their stings may cause skin rashes, muscle cramps, or even death.
Other Information
While many species live solitary lives, some like Aurelia may travel in shoals of hundreds to thousands of individuals stretching for dozens of kilometers. These mass accumulations can cause fishing problems, clogging nets and making them difficult to clean. At times, large shoals are washed ashore by storms.
Scyphozoa Links
http://www.ucmp.berkeley.edu/cnidaria/scyphozoa.html