The word "invertebrate" refers to an animal that lacks a backbone. Antonyms for invertebrate refer to animals that have a backbone. Examples of antonyms for invertebrate include vertebrate, spinal, and chordate. These animals are characterized by their internal skeleton, which offers support and protection to their body. Vertebrates are further classified into five subgroups: mammals, birds, reptiles, fish, and amphibians. They generally possess a well-developed nervous and circulatory system, a brain and a spinal cord, and are capable of movement. In contrast, invertebrates have diverse physiological characteristics, and some are capable of occupying extreme habitats such as heavily acidic or salty environments.