Characteristics of Animals

What characteristics do all animals share?

All members of the animal kingdom share certain characteristics. Animals are all heterotrophs; they obtain nutrients and energy by eating other organisms. Animals are also multicellular; their bodies are composed of many cells. The cells that make up animal bodies are eukaryotic, containing a nucleus and membrane-bound organelles. Unlike the cells of algae, fungi, and plants, animal cells lack cell walls. Animals, which are members of the kingdom Animalia, are multicellular, heterotrophic, eukaryotic organisms whose cells lack cell walls.

Types of Animals

What characteristics distinguish invertebrates and chordates?

Animal diversity is so vast and differences among animals so great that we need to divide these organisms into groups to even begin talking about them. Animals are often classified into two broad categories: invertebrates and chordates.

Invertebrates More than 95 percent of animal species are informally called invertebrates. Invertebrates include all animals that lack a backbone, or vertebral column. Because this category lumps together organisms that lack a characteristic, rather than those that share a characteristic, “invertebrates” do not form a clade or any other kind of true category in the system of biological classification. Invertebrates include at least 33 phyla, which are the largest taxonomic groups of animals. Invertebrates include sea stars, worms, jellyfishes, and insects. They range in size from dust mites to colossal squid more than 14 meters long. DOL•31–DOL•45.