1. These are bilaterally symmetrical, triploblastic, schizocoelomate, segmented animals.
2. They have organ system grade of organization.
3. They have jointed appendages.
4. Body is covered by chitinous exoskeleton. The body is divided into head, thorax, and abdomen.
5. Body cavity is filled with colorless blood. It is called hemocoel.
6. Respiratory organs are gills, book gills, book lungs, trachea.
7. Open-type circulation is seen.
8. Sense organs are present.
9. Fertilization is internal. e.g., humulus, insects.

1. The animals are marine, diploblastic and radially symmetrical.
2. They have eight external rows of ciliated comb plates which help in locomotion.
3. Bioluminescence is seen.
4. They lack nematocysts but have lasso cells which help in food capture.
5. Digestion is by both extra cellular and intracellular.
6. Sexual reproduction is seen.
7. Fertilization is external and development is indirect.
8. Cydippid larva is seen. e.g., Hemiphora.

Coelomic fluid acts as hydrostatic skeleton which helps to maintain the shape of the body

All vertebrates possess three salient features of chordates:
1. Presence of Notochord.
2. Presence of dorsal, hollow nerve cord.
3. Presence of pharyngeal gill slits in some stage of their l.ife cycle. Hence all vertebrates are chordates.
All chordates are not vertebrates:
Primitive chordates have only a notochord which is not replaced by vertebral column as seen in vertebrates. Hence all chordates are not vertebrates

1. The name of phylum Cnidaria is derived from cnidocytes or cnidoblasts with stinging cells or nematocysts on tentacles.
2. Cnidoblasts are used for anchorage, defense, and to capture the prey.