Presence of water vascular system or ambulacral system with tube feet or podia is a salient feature. This helps in locomotion, respiration, capture and transport of food.

The term 'Echinos' means spiny and 'dermos' means skin. These animals have a mesodermal endoskeleton of calcareous ossicles and hence they are called echinoderms or spiny skinned animals.

1. In Phylum Annelida, the body is metamerically segmented. The body surface is divided into segment or metameres.
2. Internally the segments are divided from one another by partitions called septa. This phenomenon is known as metamerism.

1. The female are longer than males.
2. The hind end of the male worm is curved.

1. They absorb nutrients directly from the host through their body surface.
2. Organs of attachment such as hooks and suckers are present which help to attach to host surface. Eg: Taenia.

1. In some animals, the body cavity is not fully lined by the mesodermal epithelium, but the mesoderm is formed as scattered pouches between the ectoderm and endoderm.
2. Such a body cavity is called a pseudocoel and is filled with pseudocoelomic fluid. Animals that possess a pseudocoel are called pseudocoelomates Eg: Round worms.

(i) Flame cells are found in acoelom.
(ii)They collect nitrogenous wastes from visceral parenchyma.
(iii) Excreta are transported to the lateral excretory ducts and finally ejected out by excretory pores.
(iv) When such cells collect the excreta showing flickering movements of the flame they are called as flame cells.
Eg: Planaria or dugesia belongs to the class Turbellaria of phylum Platyhelminthes.

The circulatory system is of two types,
1. Open type: The blood remains filled in tissue spaces due to the absence of blood capillaries.
Eg: Arthropods, Molluscs, Echinoderms, and Urochordates
2. Closed type: The blood Is circulated through blood vessels of varying diameters (arteries, veins, and capillaries)
Eg: Annelids, Cephalochordates and Vertebrates.

(i) Heterotrophic nutrition
(ii) Reserve food is glycogen
(iii) All animals are eukaryotes
(iv) Locomotion is the most common feature of animals

(i) Invertebrates do not have notochord and presence of notochord is the unique feature of chordates.
(ii) Cephalisation indicates the distinct head in animals
Eg: Arthropods to chordates.
(iii) dorsal nerve cord arises in chordates behind the alimentary canal.
Eg: Hemichordates and chordates but ventral nerve cord arises in non chordates infront of the alimentary canal.
Eg: Annelidans to Echinoderms.
(iv) Radial symmetry is commonly found in coelenterates or cnidarians and in most of animals of other phyla.