Mr and Mrs Smith's Life Science

SciCoralB&W.bmp (122358 bytes) Cnidarians
Jellyfish  Sea Anemone  Coral  Hydra

Class: Scyphozoan

The jelly's bell is the closest thing it has to a body. Underneath the bell, in the center, lies the only way in or out of a jellyfish - its mouth. Once inside, we find no brain, no heart and no spine - just a simple stomach and four gonads, or reproductive organs. In every other scallop along the edge of the bell, we find a bundle of sensory nerves. This bundle allows the jelly to detect light, smells and stay upright while swimming. In some jellies the bell is home to tiny crab or fish hitchhikers.

Fringing the bell is a row of tentacles. These vary in length from the slight fringe of the moon jelly to the longer tentacles of some pelagic jellies, which might reach over 100 feet. Jelly tentacles are used in food gathering and are covered with thousands (or in some cases millions) of stinging cells called nematocysts.

Four oral arms hang from the middle of a jellyfish's bell, surrounding its mouth. Oral arms are also covered with stinging nematocysts. These cells contain a hollow, barbed thread that fires on impact or in response to a chemical cue. Many are toxic, used to paralyze or kill their prey. The most toxic, the box jelly (or sea wasp) can kill a human being in minutes. Others, such as the moon jelly, won't even cause a rash.


Class: Anthozoan

Often mistaken for plants, anemones are animals. The stinging cells on their tentacles help them capture prey and defend themselves. Some reproduce sexually, others can clone themselves asexually.

Corals may not seem as though they fit the Cnidarian mold, but put them under a microscope and all becomes clear. Corals are made up of thousands of tiny polyps living in a colony. Each is complete with tentacles--stinging cells and all.

Class: Hydrozoan

They appear to be jellies, but are actually colonies of many organisms functioning as a single unit. These cnidarians vary in size from very small up to 66 feet (20 meters). Each unit is composed of many individuals, each with a different function. These functions include reproduction, feeding and defense. By working together as a single unit, a colonial organism can function more efficiently.

One example of a siphonophore is the Portuguese man-of-war, Physalia physalia. A Portuguese man-of-war is not a true jelly. This is another colonial animal with specialized polyps for feeding, stinging, and reproduction, all hanging from a gas-filled float.

Sea pen
It looks like an ostrich plume pen, but it is yet another colonial cnidarian. The center stalk roots itself in the sandy bottom and supports thousands of tiny polyps that filter feed on plankton.

The parade of colonial creatures continues with the hydroid. Hydroids are brushlike colonials that grow on pilings, rocks and shells. They have specialized polyps for feeding, , defense and reproduction.

Comb jellies
These aren't really jellies at all. In fact, they aren't even Cnidarians. They make up their own phylum, Ctenophora. which include 100 species that all have eight rows of iridescent comblike plates used in locomotion.

1. Fill in the Chart

   Scyphozoan           Anthozoan            Hydrozoan   

2. Write the definitions