Animals of the World

The animal kingdom includes millions of species, ranging from microscopic creatures to the largest mammals. Scientists classify animals into groups based on shared characteristics, beginning with the broad split between vertebrates, which have a backbone, and invertebrates, which do not. Vertebrates include fish, amphibians, reptiles, birds, and mammals, while invertebrates encompass insects, arachnids, mollusks, and many other forms that together make up the great majority of animal species.

Animals occupy nearly every habitat on Earth, from oceans and rivers to forests, grasslands, and deserts. Reptiles such as snakes, including constrictors like the boa and python, are adapted to warm environments, while mammals such as bears, big cats, and primates are found across many climates. The variety of body forms reflects different ways of feeding, moving, and reproducing: carnivores hunt other animals, while many mammals and reptiles have specialized adaptations for breeding and raising young.

Studying animals by name and group helps reveal relationships among them and the adaptations that allow each to survive. Zoos and wildlife reserves house and breed many species, including those that are rare or endangered, and support research and education. Understanding how animals are organized, from arachnids and insects to hooved mammals and marine creatures, provides a framework for appreciating the diversity of life worldwide.

Frequently asked questions

What is the difference between vertebrates and invertebrates?

Vertebrates have an internal backbone and include fish, amphibians, reptiles, birds, and mammals. Invertebrates lack a backbone and include insects, arachnids, and mollusks.

How do snakes such as boas and pythons catch prey?

They are constrictors that coil around prey and tighten their grip, rather than using venom, before swallowing the animal whole.

Why are zoos involved in breeding programs?

Captive breeding helps maintain populations of rare and endangered species and supports research and education about animals.