A. $\rightarrow$ (v) B. $\rightarrow$ (iii) C. $\rightarrow$ (ii) D. $\rightarrow$ (i) E. $\rightarrow$ (vi) F. $\rightarrow$ (iv)

A. Amphibians possess dual habitat, i.e., they are found in both aquatic and terrestrial habitat. Their larva is completely aquatic and adult lives in terrestrial as well as in aquatic habitat

B. Mammals have mammary glands which produce milk and feed their young ones. The mammary glands are enlarged exocrine modified sweat glands functional in female mammals.

C. Chondrichthyes have the cartilaginous rod (notochord) in the young stage which is gradually replaced by cartilage.

D. Osteichthyes have air bladder which is a vesicle or sac containing air,

E. Cyclostomes possess sucking and circular mouth without jaws which is surrounded by tentacles and the tongue bears teeth. e.g., lamprey and nagfish.

F. Aves have light weighted bones with internal spaces filled with air called pneumatic bones and aerodynamic lungs with specialised air sacs. These are the adaptations which enable birds to fly.

The endoparasites such as Taenia solium and Fasciola hepatica (liver fluke), etc., are found inside the host body, and survive due to the presence of certain characters.

Special characters present in by endoparasites are as folows

(i) The possess anaerobic respiration and the gaseous exchange is through general body surface.

(ii) These organisms bear additional organ for the attachment to the host. Fasciola hepatica possesses acetabulum or posterior sucker for the attachment. Taenia solium posses hooks and suckers for the attachment with the host.

(iii) Reproductive organs are well developed. They are generally, hermaphrodite and self fertilisation is common in them.

(iv) The thick tegument (body covering) is present which is resistant to the host's digestive enzymes and antitoxins.

(v) Absence of locomotary organs.

(vi) Tapeworms lack digestive organs because digested and semidigested food of the host is directly absorbed through their because body surface.

A. $\rightarrow(\mathrm{v})$ B. $\rightarrow$ (ii) C. $\rightarrow$ (iii) D. $\rightarrow$ (iv) E. $\rightarrow$ (ii) F. $\rightarrow$ (vi)

A. Pila-Presence of shell Shell in Pila is an elongated structure which consists of a tubular whorl coiled around a central axis called columella. The main function of shell is to provide protection from harsh conditions.

B. Cockroach-Jointed appendages Presence of jointed appendages along with segmented body is the characteristic feature of arthropods (e.g., spiders, bees, crabs etc).

C. Asterias-Water vascular system It is the unique and characteristic feature in echinoderms. This system acts as a hydraulic system, composed of canals connecting numerous tube feet. It is very important as it helps Asterias (sea star) to move as well as to catch food. Respiration also takes place, through, water vascular system.

D. Torpedo Electric organ. Torpedos are unique organisms, having two large kidney shaped electric organs. These organs are capable of generating high voltage electric shocks.

E. Parrot-Perching Birds with the feet adapted (to hold tree branches are perching birds. The Passeriform birds are true perching birds with four toes, three directed forward and one backward.

F. Dog fish-Placoid scales Placoid scales are tough scales that cover the skin of elasmobranchs (dog fish, sharks and rays). They are covered with hard enamel. The function of these scales is to protect against predators.

Characteristic features of different classes mentioned are as follows

(a) Chondrichthyes

(i) These are marine animals with a stream lined body.

(ii) Body is has cartilaginous exoskeleton and the skin is tough due to the presence of minute placoid scales.

(iii) These animals are predaceous.

(iv) Due to the absence of air bladder they have to swim constantly to avoid sinking.

(v) They are cold blooded animals e.g., Scoliodon (dog fish), Pristis (saw fish).

(vi) Some of them possess electric organs and poison sting (Torpedo and Trygon).

Osteichthyes

(i) These animals are found in both habitats, i.e., marine and freshwater. They bear bony endoskeleton.

(ii) Body is streamlined, posseses four pairs of gills covered by an operculum, on each side.

(iii) Skin is covered by cycloid or ctenoid scales.

(iv) Presence of air bladder is an additional feature providing buoyancy to animal.

(v) Heart is two chambered.

(vi) Sexes are seperate, fertilisation usually external, oviparous animal with direct development.

e.g., marine- Exocoetus (flying fish), Hippocampus (sea horse); freshwaterLabeo (rohu).

(b) Urochordata

(i) In urochordates, notochord is only present in larval tail.

(ii) They contain a tough outer covering called tunic.

(iii) Persence of pharyngeal slits during some stage of the life cycle and a muscular, post anal tail is the characteristic features in urochordates.

e.g., Salpa, Ascidia, Doliolum.

Cephalochordata

(i) Cephalochordates are exclusively marine animals.

(ii) The notochord in cephalochordates extends, from the heart to tail region and is persistent throughout the life.

(iii) Body-wall shows one cell thick, non-ciliated epidermis, connective tissue, striated muscle and parietal peritonium.

(iv) Fertilisation is external

e.g., Branchiostoma (Amphioxus or Lancelet).