Criteria for new system of classification :
A. Grades of organization :
- Protoplasmic grade' of organization : unicellular organisms - Amoeba, Paramecium
- Cellular grade organization : multicellular animals in which tissues are not formed -Ex. Phylum-Porifera.
- Cell - tissue grade’ organization : cells come together to form tissues - Ex. Animals from phylum- Cnidaria.
- Tissue Organ grade’ organization : tissues are organized to form some organs - Flat worms.
- Organ - system grade organization : different organs are joined together to form organ system - Ex. Crab, Frog, Human, etc.
B. Body Symmetry :
- Asymmetrical Body : no any imaginary axis of the body through which we can get two equal halves. - Ex. some sponges.
- Radial symmetry : if imaginary cut passes through central axis but any plane of body [five different planes], it gives two equal halves. Ex. Star fish.
- Bilateral symmetry : there is only one such imaginary axis of body through which we can get two equal halves. - Ex. Insects, fishes, frog, birds, human, etc.
C. Germ Layers:
- Diploblastic : only two germ layers [Endoderm & ectoderm] are formed during initial period of their embryonic development.- Ex.: All Cnidarians.
- Triploblastic : Three germ layers are formed i.e. mesoderm besides endoderm & ectoderm. Ex- In most of all the remaining animals.
D. Body cavity (Coelom) :
- Eucoelomate [animals with true body cavity ] : Body cavity is formed from either mesoderm. Ex- phylum Annelida and all phyla coming after Annelida
- Acoelomates : Body cavity is absent. Ex - animals from phyla Porifera, Cnidaria and Platyhelminthes.
- Pseudocoelomates : they have body cavity but it is not formed by the above mentioned two ways. Ex - Animals from phylum Aschelminthes.
E. Body Segmentation :
- Segmented : Body of animals is divided into small, similar units, segment. - Ex. Animals like earthworm from phylum Annelida.
- Non-Segmented : Body of animals is Not divided into small, similar units. - Ex -