, the true jellyfish. Click on the buttons below to learn more about Cnidaria. Visit the for information and links dealing with all manner of cnidarians. Visit the home page of the. Casually touching many cnidarians will make it clear how they got their name when their nematocysts eject barbed threads tipped with poison. Many thousands of cnidarian species live in the world's oceans, from the tropics to the poles, from the surface to the bottom. Some even burrow. Cnidarians are incredibly diverse in form, as evidenced by colonial, massive and, feathery, and with. Yet, these diverse are all armed with stinging cells called nematocysts. Introduction about life essay. Cnidarians are united based on the presumption that their nematocysts have been inherited from a single common ancestor. The name Cnidaria comes from the Greek word cnidos, which means stinging nettle.
A smaller number of species are found in rivers and fresh water lakes. There are four major groups of cnidarians:
, which includes true corals, anemones, and sea pens;
, the amazing box jellies with complex eyes and potent toxins;
, the most diverse group with siphonophores, hydroids, fire corals, and many medusae;