Animalia synapomorphies[1, chap32]
Animals differ from other eukaryotes in many ways:
- Multicellularity: This separates them from many protists.
- Lack of cell walls: Plants and fungi both have cell walls, made of cellulose or chitin. Animal cells are held together by proteins, most notably collagen, which is also unique to animals.
- Mode of nutrition: Animals do not produce their own energy. They are heterotrophic, as are fungi, but decomposers among fungi digest nutrients while they are still outside the organism, and then absorb them. Animals consume and then digest.
- Specialized tissues: Nerve and muscle tissue are unique to animals.
Several characteristics also separate animalia into different groups:
- Development patterns: True tissues spawning from germ layers in the embryo excludes sponges from the rest of the kingdom (eumetazoans, true + animal), and spiral cleavage distinguishes deuterostomes from other bilateral animals.
- Body plans: Bilateral animals form a clade within the eumetazoans.
- Particular structures or processes: Ecdysis is shared by ecdysozoans but not found in lophotrochozoans. A notochord and dorsal nerve cord signify chordates.
References
[1]Campbell & Reece, Biology 8th Edition