Summary
Multicellular heterotrophic eukaryotes without cell walls that typically move and ingest food.
In depth
Animals are multicellular heterotrophs with cells lacking walls, extracellular matrix with collagen, nerve and muscle cells (except sponges), and typically sexual reproduction with a distinctive embryonic development. Around 1.5 million species are described; the real number may be several million.
Animals evolved from colonial choanoflagellate-like ancestors.
Animals are grouped into about 35 phyla. Body plans differ in symmetry, germ layers, cavities and development. Evolution from simple to complex is not linear.
Key idea: animals share heterotrophy and multicellularity.
About 1.5 million animal species are described, and estimates for the total range from 7 to 10 million, with insects the largest group. Animals appeared in the oceans more than 600 million years ago, with the Cambrian explosion adding most body plans. Features define the group: ingestive heterotrophy, collagen and cell junctions, Hox genes, and embryonic development through a blastula. Major lineages are sponges, cnidarians, and the bilaterians divided into protostomes and deuterostomes.
Animals shape ecosystems as herbivores, predators, pollinators, decomposers and engineers, and provide food, materials, models for research and companionship. Classification by body plan (symmetry, germ layers, coelom, segmentation) is supported by molecular data.
Example: the 35 or so animal phyla differ more in body plan than in species number, and arthropods alone hold over 80 percent of species.
Frequently asked questions
What is Animal Kingdom?
Multicellular heterotrophic eukaryotes without cell walls that typically move and ingest food.
Which area of biology covers Animal Kingdom, and how advanced is it?
Animal Kingdom is one of the 53 topics in Zoology & Animal Diversity. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Vertebrates and Invertebrates, Protostomes and Deuterostomes, Insects.
Can you give an example of Animal Kingdom?
Most animals are insects.
What should I learn before Animal Kingdom?
Animal Kingdom is a Beginner topic, so no earlier topic is required. Other Beginner topics in Zoology & Animal Diversity that pair well with it include Vertebrates and Invertebrates, Sponges, Cnidarians.
What topics are related to Animal Kingdom?
The closest topics to Animal Kingdom are Vertebrates and Invertebrates, Protostomes and Deuterostomes, Insects, Germ Layers. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Animal Kingdom?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Animal Kingdom. To practise the whole of Zoology & Animal Diversity, use the Zoology & Animal Diversity quiz.
How is Animal Kingdom different from Vertebrates and Invertebrates?
Animal Kingdom: Multicellular heterotrophic eukaryotes without cell walls that typically move and ingest food. Vertebrates and Invertebrates: Vertebrates have a backbone; invertebrates, which are over 95 percent of animals, do not. Read both side by side and note what each one explains.
How should I study Animal Kingdom step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Vertebrates and Invertebrates and explain the difference aloud. Finally, take the Zoology & Animal Diversity quiz and come back to this page for any question you miss.