Definition
The class Echinoidea encompasses sea urchins, sand dollars, and other closely related marine animals. These creatures are characterized by their rigid skeletons, typically covered with spines or bristles. Think of them as the porcupines of the sea! 🌊 They exhibit pentaradial symmetry, a hallmark of echinoderms. Unlike vertebrates, they lack a centralized brain but possess a complex nervous system. They inhabit a wide range of marine environments, from shallow tide pools to the deep ocean floor. They are important grazers and detritivores, playing a crucial role in marine food webs.