All animals are classified as vertebrates, which are mostly animals but also include birds, reptiles, mollusks, and some fishes. All vertebrates belong to the Kingdom Animalia, a division of the Phylum Chordata, which is a class of animals that are not true mammals. Animals are multicellular, meaning they have multiple skeletal systems including a skeleton and muscles. With few exceptions, all animals breathe oxygen, consume organic matter, can move, reproduce sexually, and consume their own food.

The three domains of the animal kingdom are Phylum (phyto), Class (stratum) and Subclass (metacarpal) and there are 60 different types of animals in each domain. Animals are classified on the basis of their arrangement of limbs, but most animals are properly classified according to the classification scheme of the animal kingdom. For example, whales and dolphins are in the Phylum Chordata, but they are categorized as a separate class of mammals. In the Class Stem Cells, there are two categories of animals: Balaenoptera and Cetacea.

The class of animal kingdom also includes several classes of unicellular organisms, which are grouped together based on similarities of body plan. These animals are placed in the Kingdom Animalia, the same as insects and fishes, but here the animals are classified on the basis of their mode of reproduction. Among these, there are two major classifications of animals: Multicellular and unicellular. Multicellular animals reproduce by means of a series of cells while unicellular animals reproduce through a single cell.

The majority of animals belong to one of the classes of animalia. Among these are several unicellular animals that belong to the Kingdom Animalia. Among the animals in this kingdom are both fishes and amphibians. The most important classification of animals is the vertebrates, which are classified as a group of mammals and they have evolved in the Eukaryota (omni-plant) phylum. The other animals in this kingdom are the fishes, the amphibians, some eels and crocophilians, such as clams and oysters.

Other animals include reptiles, amphibians, cephalopods, mollusks, crustaceans, unicellular organisms and some echinoderms. The unicellular organisms are in this kingdom animalia with a protoplant (keratin) which is the major component of their exoskeleton. The animal kingdom has many more specialized sensory organs than this, such as the eyes, ears, olfactory organs, sense of taste, nose, tongue and lung.

The different animals have evolved over the course of evolution. Some are adapted to live on land, some can survive in water, some are adapted for aquatic habitats and amphibians and vertebrates are both terrestrial and aquatic animals. Among all these animals, the most common types are birds, whales, cats, dogs, insects, amphibians, and some unicellular organisms. Insects such as mosquitoes are important contributors to the control of animal diseases. By preventing animal disease, mosquitoes help to reduce the spread of animal diseases.