This document describes the key characteristics of the five classes of vertebrates: fish, reptiles, amphibians, birds, and mammals. For each class, it outlines their habitat, body covering, limb structure, and circulatory and temperature regulation systems. The main habitats are aquatic for fish, both aquatic and terrestrial for reptiles and amphibians, terrestrial for birds and mammals. Body coverings include scales, skin, feathers, and fur or skin. Limb structures vary from fins to legs to wings. Circulatory systems are either cold-blooded for fish, reptiles and amphibians or warm-blooded for birds and mammals.