The phylum Cnidaria contains approximately 9000 living species worldwide. They are among the simplest of the higher organisms, but are also among the most beautiful. The creatures in this phylum are radially symmetrical. This means that the parts of the body extend outward from the center. A common example of radial symmetry is the sea star.
The Cnidarians include the hydroids, jellyfish, anemones, and corals. All Cnidarians have tentacles with stinging cells in their tips which are used to capture and subdue prey. The phylum name "Cnidarian" literally means "stinging creature." The stinging cells are called cnidocytes. The nematocyst is a coiled thread-like stinger. When the nematocyst is engaged, it uncoils, and shoots out. The thread goes through the cnidocyte wall and into the prey. Most Cnidarians also have a toxin in their stinger which helps to disable the prey.
Cnidarians have a one way digestive system, this means that undigested food and digested food are passed through the same opening. This one way digestive tract is called the Gastrovascular Cavity. Cnidarians are predators and use many different nematocysts to puncture, jab, stick to, and entrap their prey. These nematocysts inject a toxic chemical which stuns or kills their pray. Once captured, food is passed into the Gastrovascular Cavity and digested.
The Cnidarians include the hydroids, jellyfish, anemones, and corals. All Cnidarians have tentacles with stinging cells in their tips which are used to capture and subdue prey. The phylum name "Cnidarian" literally means "stinging creature." The stinging cells are called cnidocytes. The nematocyst is a coiled thread-like stinger. When the nematocyst is engaged, it uncoils, and shoots out. The thread goes through the cnidocyte wall and into the prey. Most Cnidarians also have a toxin in their stinger which helps to disable the prey.
Cnidarians have a one way digestive system, this means that undigested food and digested food are passed through the same opening. This one way digestive tract is called the Gastrovascular Cavity. Cnidarians are predators and use many different nematocysts to puncture, jab, stick to, and entrap their prey. These nematocysts inject a toxic chemical which stuns or kills their pray. Once captured, food is passed into the Gastrovascular Cavity and digested.