Nat Demirgian, age 13, of Gadsden, Ala., for his question:
WHAT IS A MEDUSA?
Medusa is the name biologists give tj the common jellyfish. Jellyfish can range in size from a giant in Arctic waters that may be about seven feet in diameter to some that are no larger than a pea.
Jellyfish get their names from the jellylike material between the two layers of cells that make up the animal's body. The substance serves as a skeleton to support the fragile body wall.
The body of a medusa looks something like a bell or umbrella. A short tube, which contains the mouth, hangs from the center of the body like a bell clapper. The edges of this tube form four frilly projections called oral arms.
The medusa then has another group of projections, called tentacles, that hang down from the edges of the body. Each kind of jellyfish has a certain number and length of tentacles.
Jellyfish are classified as coelenterates, a phylum that includes corals, sea anemones and hydras. Large jellyfish make up a class called scyphozoan jellyfish. These sea animals are often seen at the coast and are sometimes called sea nettles. Sea nettles are about the size of soup bowls and they may be pale orange, pink, blue or other colors.
A medusa will swim by expanding the body like an opening umbrella, then pulling it together again rapdily. This squeezes water out from beneath the body and the animal is able to move forward. When these movements stop, the jellyfish slowly sinks to the bottom.
On the way to the bottom, the jellyfish will catch small animals that touch its tentacles or oral arms. These parts contain stinging cells that explode when they touch a victim. The explosion drives tiny poisonous threads into the victim and paralyzes it. The victim is then passed to the mouth of the jellyfish.
Some jellyfish can inflict painful and even dangerous stings to people.
One type of jellyfish is called the sea wasp. This creature can inject its victim with a poison that is deadlier than any snake venom. Some victims have died less than three minutes after being stung by a sea wasp. Sea wasps are found near the coasts of northern Australia and the Philippines.
The polyorchis jellyfish, found along the United States Pacific Coast, looks like an electric light bulb. Its mouth is at the lower end of a long, slender stalk that can be seen inside the "bulb." Its tentacles catch food and pass it up to the mouth.
The obelia jellyfish grows to be about one twentieth of an inch, which is about the size of a pinhead.
Scyphozoan jellyfish produce their young from eggs. These eggs develop into tiny polyps, which attach to the sea bottom. The jellyfish grow from the polyps by a process called budding. They are arranged on each polyp like a stack of saucers.
The jellyfish, when they reach a certain size, are released from the polyp and develop into adults.