Kingdom Animalia encompasses a vast diversity of complex organisms, divided into vertebrates (animals with backbones) and invertebrates (animals without backbones). Vertebrates include mammals, birds, reptiles, amphibians, and fishes, while invertebrates are categorized into several phyla, including echinoderms, arthropods, mollusks, annelids, nematodes, platyhelminthes, cnidarians, and poriferans. Each group exhibits unique characteristics, reproductive methods, and habitats, contributing to the ecological balance of their environments.