The Phylum Cnidaria consists of over 9,000 species of water creatures which are often mistaken for floating plants because of their long tentacles and flower- like body shapes. Although there are many different cnidarians there are only two different body forms; Medusae and Polups. Most jellyfish are classified as Medusae jellyfish which have an umbrella like form with a mouth on the under side and tentacles surrounding the mouth. Sea anemones usually have polyp shaped bodies with long tube like immobile forms that have flowing tentacles that are necessary to catch food with. The polyp form of cnidarians reproduce asexually while the medusae form reproduce sexually. Although cnidarians are undeniably beautiful, they also are quite dangerous. The word Cnidaria means 'stinging animal' and although their stinging cells are used in capturing food, they are often used in defense and have the capacity to harm a human quite badly. Many cnidarians can range in size from a microscopic organism to aroung seven feet long. Cnidarians are classified into Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa groups which is based on whether each cnidarian was cleary a medusae or polyp form.
The Phylum Cnidaria consists of jellyfish, hydra, sea anemones, and corals. These animals first appeared on earth an esstimated 500 million years ago and are still reproducing and evolving today. Cnidarian polyps survive by attaching themselves to hard matter on the ocean floor and eaither catching food or protecting other cnidarians. Medusae jellyfish swim openly in the water and these jellyfish have recieved their name because of the thick liquid substance under their first layer of skin. The Phylum Cnidaria may be simple creatures but they have been enormously successful in evolution.
