The video "What Are Echinoderms?" explores the fascinating world of echinoderms, which include well-known species such as the starfish. Echinoderms are marine invertebrates known for their unique radial symmetry, allowing their bodies to be divided into five identical parts, similar to a pizza. These organisms inhabit ocean environments exclusively and possess a water vascular system used for movement, feeding, and respiration through tube feet. The video discusses echinoderms' spiny skin and various defense mechanisms against predators, such as chemical defenses and unique behaviors like those of the sea cucumber. The educational content highlights the importance of understanding echinoderms' biological characteristics and their role in marine ecosystems.