(From the Clade Choanoformes, Kingdoms of Life, and Organismic Biology pages.)
Zoology is the study of animal life. Animals are multicellular, heterotrophic eukaryotes that do not utilize cell walls in their anatomy, that are motile in at least one stage of development, and which pass through a blastula stage of embryonic growth - one of the six Kingdoms of Life living today.
Animals differ from plants in that, although both are multicellular, animal cells, like all their filozoan ancestors, do not possess cell walls, allowing animal tissues to utilize a more complex inter-cellular signaling at cellular junctions. Filozoans and their amoeboid relatives make up for the lack of a cell wall by utilizing a sophisticated cytoplasmic skeleton composed of actin and tubulin filaments which also permits the development of more complex cell types that require a very organized method of segregating and transporting cell components, such as nerve and muscle cells.
The following are the largest morphologic groupings of organisms in the Animal Kingdom. For a taxonomic progression that more closely demonstrates the evolution of animals from their earliest common ancestors, start with the Invertebrate grouping:
- ↑ The invertebrate clade is polyphyletic and, as organized by this outline, contains the vertebrates as a sub-taxonomic clade of the more general classes of animals within which it is contained.
- ↑ Not monophyletic.
- ↑ Although the listing of Vertebrata here as a subclade of Animalia is the conventional taxanomic assignment, in fact it is not properly grouped as such in a strictly monophyletic taxonomy where it should be listed as a subclade of Craniata (itself a subclade of Chordata), since Vertebrata shares a common ancestor with the other clades of Craniata.