1. They are small fish like coelomate forms with chordate characters like notochord, dorsal tubular nerve cord and pharyngeal gill slits throughout their life.
2. Closed type of circulatory system is seen without heart.
3. Excretion is by protonephridia. Eg: Amphioxus

The Ctenophores have eight external rows of ciliated comb plates (comb jellies) in the mesoglea which help in locomotion. Hence they are commonly called as comb jellies or sea walnuts.

Polyp and Medusa are two basic body forms found in phylum cnidaria. Cnidarians which exist in both forms also exhibit alternation of generations in their life cycle

Polyp	Medusa
1. Asexual generation	Sexual generation.
2. Cylindrical in shape.	Umbrella-shaped.
3. It is a fixed zooid.	It is a free swimming form.

1. In Phylum Porifera organisms possess a water transport system or canal system where water enters through minute pores called ostia lining the body wall through which the water enters into a central cavity (spongocoel) and goes out through the osculum.
2. This water transport system is helpful in food, gathering, circulation, respiration, and removal of waste.

(i) Feathered vertebrates like birds have endoskeleton.
(ii) Flying birds have air filled hollow bones due to extension of air sacs of lungs. These bones are called as pneumatic bones.
(iii) In flying birds bones are very much demineralised.
(iv) In flying birds striated flight muscles well attached with carina of sternum.
(v) While in flightless birds bones are hard, compact and not filled by air but striated muscles are well attached to bones for leading, running and walking.

(i) Bony fishes belongs to osteichthyes.
(ii) Notochord is replaced by skeletal system.
(iii) Body is spindle shaped.
(iv) Skin is covered by ganoid, cycloid and ctenoid scales.
(v) 4 paired filamentous gills covered by operculum to perform respiration.
(vi) Air bladder is independent to gut or dependent to gut.
(vii) Heart is ventral and two chambered.
(viii) Mesonephric kidneys excrete NH₃.
(ix) Lateral line sense organs are well developed (choose any three features).

(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.

(i) Eggs or young ones produced by an oviparous (egg laying)and viviparous (directly yield young ones) female animals may not be equal.
(ii) Numerous eggs are laid by oviparous, so the number of produced offsprings is indefinite.
(iii) Eggs laid by oviparous, female may not develop into adults due to predators.
(iv) Oviparous female includes polyembryony.
(v) Viviparous produced by females need protection from predators associated with parental cares.
(vi) Development of young ones of oviparous female occurs in environment whereas the development of young ones of viviparous female occurs in the female reproductive system of adults.

(i) The larva trochophore belongs to the phylum annelida.
(ii) In the class Polychaetae of phylum annelida the fertilization is internal and the development is indirect due to the presence of larva trochophore.