How are animal classified on the basis of presence or absence of the backbone in their bodies?

Animals are classified into two main groups based on the presence or absence of a backbone: vertebrates and invertebrates. Vertebrates, which include mammals, birds, reptiles, amphibians, and fish, possess a backbone or spinal column. Invertebrates, on the other hand, lack a backbone and include diverse groups such as insects, arachnids, mollusks, and crustaceans. This classification helps in understanding the structural and functional diversity of the animal kingdom.