Fascinating Facts About Jellyfish, Part II

Jellyfish live mainly in the ocean, but they aren't actually fish -- they're plankton. These plants and animals either float in the water or possess such limited swimming powers that currents control their horizontal movements. Some plankton are microscopic, single-celled organisms, while others are several feet long. Jellyfish can range in size from less than an inch to nearly 7 feet long, with tentacles up to 100 feet long!

Jellyfish are about 98 percent water. If a jellyfish washes up on the beach, it will mostly disappear as the water evaporates. Most are transparent and bell-shaped. Their bodies have radial symmetry, which means that the body parts extend from a central point like the spokes on a wheel. If you cut a jellyfish in half at any point, you'll always get equal halves. Jellyfish have very simple bodies -- they don't have bones, a brain or a heart. To see light, detect smells and orient themselves, they have rudimentary sensory nerves at the base of their tentacles.


A jellyfish's body generally comprises six basic parts:

• The epidermis, which protects the inner organs
  
• The gastrodermis, which is the inner layer
  
• The mesoglea, or middle jelly, between the epidermis and gastrodermis
  
• The gastrovascular cavity, which functions as a gullet, stomach, and intestine all in one
  
• An orifice that functions as both the mouth and anus
  
• Tentacles that line the edge of the body