What is the animal kingdom?

The animal kingdom comprises multicellular eukaryotes that generally obtain food from other organisms or organic matter and, in many cases, can move.

Shared traits and great diversity

Animal cells have nuclei and lack rigid cell walls of the kind found in plants. Rather than producing food by photosynthesis, animals obtain it externally; digestion, movement and sensory abilities vary widely. Sponges, insects, molluscs, fish, birds and mammals all belong to this kingdom. Vertebrates are familiar, but much animal diversity lies among invertebrates. Classification uses anatomical and genetic evidence to explain shared ancestry and relationships.

Roles in ecosystems

Animals participate in communities by grazing, hunting, pollinating, dispersing seeds or breaking down dead organic matter. A species may use different habitats during different life stages. To understand an animal, examine its diet, reproduction, behaviour and environmental relationships as well as its appearance. Counting every animal in an ecosystem is often difficult; small and little-studied species are also part of its ecological network.