∞ generated and posted on 2016.08.31 ∞
Chemoheterotrophic, multicellular organisms that possess an actively motile and multicellular juvenile form.
There actually are quite a number of ways to define or be an animal, but multicellular, at some point motile (other than just as sperm or zoospores), and chemoheterotrophic are sufficient to distinguish them from protozoa, fungi, and plants, respectively (and also algae).
We can also consider animals in terms of their common anatomy:
The animals are distinguished into numerous phyla, which is the major taxonomic category (i.e., domain, kingdom, phylum, class, order, family, genus, species). These include, for example,
phylum Porifera (the sponges)
phylum Cnidaria (the jellyfish, etc.)
phylum Platyhelminthes (the flatworms)
phylum Nematoda (the roundworms)
phylum Annelida (the segmented worms)
phylum Mollusca (the mollusks)
phylum Arthropoda (the insects, etc.)
phylym Echinodermata (the starfish, etc.)
phylum Chordata (the vertebrates, etc.).