Crustaceans are a diverse group of arthropods characterized by their chitinous exoskeleton, segmented body, and motile limbs. They are found in a variety of aquatic habitats around the world, including both freshwater and marine environments. Crustaceans have advanced features like bilateral symmetry, specialized organ systems, and cephalization that aid in motility, digestion, and sensing their surroundings. Their specialized structures include limbs for movement, compound eyes and antennae for perception, and an exoskeleton for protection.