There are about ten thousands species of cnidarians. Fresh water hydras, jellyfish, sea anemones, and corals are just a few examples of some of the animals which belong to this particular phylum. This phylum is also known as coelenterates.
All the animals within this group are characterized as having tentacles with stinging cells. They have only one opening into their digestive cavity. This opening has to serve as both the mouth and anus. Their body walls are made up of at least two layers. The outer layer forms the body covering called an ectoderm, and an inner called an endoderm which lines the digestive cavity. Some cnidarians possess a third layer consisting of a stiff, jellylike material which helps support the animal.
Cnidarians come in two forms, shaped like a polyp, or medusa. The medusa looks like a mushroom with tentacles streaming down from below. Polyps are shaped like vases and usually live attached to a surface. Most cnidarians are shaped like polyps during their larval stage, and develop into the medusa form later in its life. The medusa, or jellyfish shaped cnidarians have a bell or umbrella-shaped body. Their mouths are found underneath their bell-shaped heads, which are usually surrounded by tentacles with stinging cells.
Cnidarians come in two forms, shaped like a polyp, or medusa. The medusa looks like a mushroom with tentacles streaming down from below. Polyps are shaped like vases and usually live attached to a surface. Most cnidarians are shaped like polyps during their larval stage, and develop into the medusa form later in its life. The medusa, or jellyfish shaped cnidarians have a bell or umbrella-shaped body. Their mouths are found underneath their bell-shaped heads, which are usually surrounded by tentacles with stinging cells.