Kingdom animalia are multicellular eukaryotes. They have ingestive, heterotrophic nutrition. They have the power of locomotion. They show increased sensitivity through nervous system.
Basis of Classification of Animals
Organization, symmetry, body cavity, number of embryonic cell layers and presence or absence of notochord are the features used for distinguishing broad categories of animals.
Bodies of animals are multicellular. Cells may or may not be organised into tissues and organ systems. Animals such as sponges are aggregates of cells. These are at cellular level of organisation. Cnidarians have groups of cells performing specialized functions. They are at tissue level of organisation. All other animals have organs and systems for performing body functions. They are at organ-system grade.
Symmetry means dividing the body into two equal and identical parts. Sponges are asymmetrical. Cnidaria and Echinoderm larvae are radially symmetrical. All other animals are bilaterally symmetrical or dorsiventral.
Body Cavity or Coelom
It is a cavity between body wall and food canal. It is not present in Acoelomates and is present in Eucoelomates. Pseudocoelom is not a true body cavity. It is found in roundworms.
Three layers of cells, ectoderm, mesoderm and endoderm in the embryo (germinal layers) give rise to various parts of the body of the animals. Sponges and Cnidaria do not have mesoderm in their embryos. They have two germinal layers ectoderm and endoderm (diploblastic). Others have three germinal layers (triploblastic).
It is a solid found in embryonic stage or adults of some animals which are grouped as phylum Chordata. All animal groups lacking notochord are termed non-chordates.