The video "What Are Cnidarians?" introduces viewers to Cnidaria, a fascinating phylum comprising over 10,000 aquatic species found in freshwater and saltwater environments. The central concept highlighted is the unique cnidocytes, specialized stinging cells used by cnidarians to capture their prey. The video explores the five classes of cnidarians, explaining how species like jellyfish occupy four of these classes. It delves into the anatomy and physiology of cnidarians, discussing their symmetrical body shapes, simple nervous systems, and remarkable regenerative abilities. Additionally, the video explains the ecological significance of cnidarians, such as coral reefs providing crucial benefits like habitat protection and tourism. With engaging examples and interesting trivia, this educational content elucidates the role cnidarians play in marine life, making it both informative and enjoyable for discovery in both biology and marine life education contexts.