Animals are a group of living organisms with much variety. Despite their differences, animals have certain traits in com-mon. For example, all animals have a similar cell that does not include a cell wall. Their similarities show that animals descended from a common ancestor. Animals originated from chordates, which were organisms that have a notochord. Animals are classified into phyla, depending on characteristics such as having a vertebral column or not.
Animals: A kingdom of multicellular eukaryotes.
Invertebrates: Animals that lack a vertebral column.
Vertebrates: Animals that have a vertebral column.
Vertebral Column: Another name for backbone.
Exoskeleton: Non-bony skeleton that forms on the outside of the body.
Chordate: An animal with a notochord.
Notochord: A rigid rod that runs down the entire body.
Cranium: A bony skull that protects and encloses the brain.
Amniotes: Animals that produce eggs with internal membranes, which allow them to stay on land to reproduce as opposed to finding water.
Synapsids: One of the two groups that evolved from amniotes and eventually evolved into mammals.
Sauropsids: One of the two groups that evolved from amniotes. Sauropsids evolved into reptiles, dinosaurs, and birds.
Animals are heterotrophs because they do not make their own food or nutrients. They get their energy and nutrients from consuming other living things.
Animal cells have a nucleus and other membrane-bound organelles, but unlike plants and fungi, they do not have a cell wall.
This is what gives animal cells flexibility to take on different shapes to complete different jobs.
There are more than 30 phyla under the animal kingdom, but below are the 9 largest (each phylum has more than 10,000 species).
Animals can be classified as invertebrates or vertebrates depending on the presence of a vertebral column.