Anthozoa is a class of marine invertebrates that includes organisms such as corals and sea anemones. They are characterized by their polyp form, which is a cylindrical body with a mouth surrounded by tentacles. Anthozoans are primarily found in ocean environments, often forming large colonies that contribute to coral reefs. Anthozoans are unique because they do not have a medusa stage, which is common in other cnidarians like jellyfish. They reproduce both sexually and asexually, and many species play a crucial role in marine ecosystems by providing habitat and shelter for various marine life.