* Body structure: Vertebrates have a backbone, while invertebrates do not. Vertebrates include fish, amphibians, reptiles, birds, and mammals. Invertebrates include insects, spiders, worms, mollusks, and crustaceans.
* Size: Animals can range in size from microscopic to massive. The largest animal is the blue whale, which can grow up to 100 feet long and weigh up to 400,000 pounds. The smallest animal is the etruscan shrew, which is only about 2 inches long and weighs about 0.2 ounces.
* Shape: Animals come in all shapes and sizes. Some are long and thin, others are short and round. Some have wings, others have fins, and still others have legs.
Behaviorally
* Communication: Animals communicate with each other in a variety of ways. They may use vocalizations, body language, or scent marking.
* Reproduction: Animals reproduce in a variety of ways. Some give birth to live young, others lay eggs. Some animals are monogamous, while others are polygamous.
* Social behavior: Some animals are solitary, while others live in groups. Social animals may cooperate to find food, defend themselves from predators, or raise their young.
* Diet: Animals eat a variety of foods. Some are carnivores, some are herbivores, and some are omnivores.
Ecologically
* Habitat: Animals live in a variety of habitats. Some live in forests, others live in deserts, and still others live in oceans.
* Adaptation: Animals have evolved a variety of adaptations that help them survive in their environment. Some animals have thick fur to keep them warm in cold weather, others have sharp claws to help them catch prey, and still others have camouflage to help them hide from predators.
Animals are diverse and fascinating creatures. They play an important role in the environment, and they are an integral part of our planet.