:  Cnidarians
The Cnidarians are divided into 3 broad classes: Hydras, Sea Anemones, Jellyfish, Corals. Below are links to the descriptions of the different groups.

Class: Hydrozoa, Order: Hydrocorals, Examples: Hydroids, Hydras, Hydrocorals
Class: Scyphozoa, Order: Jellyfish, Examples: Jellyfish, Box Jellyfish, Jellies, Upside-down Jellies
Class: Anthozoa, Order: Octocorals, Examples: Octocoral, Soft Coral, Gorgonian, Sea Fan, Sea Plume, Sea Pen, Finger Leather Coral, Carnation Coral, Cauliflower Coral, Tree Coral, Leather Coral, Star Polyp, Mushroom Coral, Cabbage Leather Coral, Finger Leather Coral, China Coral
Class: Anthozoa, Order: Colonial Anemones, Examples: Button Polyps, Colonial Anemones, Snake Polyps, Tube Polyps, Sea Mat, Yellow Polyps
Class: Anthozoa, Order: Mushroom Corals, Examples: Mushroom Coral, Corallimorphs, Ricordea, Rhodactis, Actinodiscus
Class: Anthozoa, Order: Stony Corals, Examples: Stony Coral, Cauliflower Coral, Bird's Nest Coral, Finger Coral, Staghorn Coral, Velvet Coral, Montipora, Pineapple Coral, Torch Coral, Hammer Coral, Frogspawn Coral, Moon Coral, Plate Coral, Brain Coral, Open Brain Coral, Lobed Brain Coral, Closed Brain Coral, Sun Coral
Class: Anthozoa, Order: Anemones, Examples: Anemone, Bubble-tip Anemone, Rose Anemone, Carpet Anemone
Class: Anthozoa, Order: Black Corals, Examples: Whip Corals, Wire Corals, Black Corals