The common characteristic of all arthropods is their exoskeleton, which is a hard outer structure made of chitin. This exoskeleton provides protection, support, and prevents water loss, critical for survival in various habitats. Arthropods also possess jointed appendages, segmented bodies, and a nervous system that supports complex behaviors. They include diverse groups such as insects, arachnids, crustaceans, and myriapods, making them the largest phylum in the animal kingdom. Their adaptability and biodiversity play significant roles in many ecological systems.