(3)

Phylum Chordata includes both jawless vertebrates (Agnatha) and jawed vertebrates (Gnathostomata). Crocodile of Class Reptilia has four-chambered heart with two auricles and two ventricles. Duck-billed platypus and spiny anteater are oviparous mammals.

(1)

Parapodia are flattened, fleshy, vertical flap-like outgrowths of body wall found in annelids on lateral sides of trunk segments. These are hollow structures enclosing coelom which is continuous with that of trunk segments. These serve the dual purpose of locomotion and respiration.

(4)

Phylum Porifera (the sponges) has cellular level of body organisation, with inner cellular layer consisting of highly specialised flagellated cells called choanocytes (or collar cells). The development in this phylum is indirect as it includes a free swimming larva called amphiblastula or parenchymula for dispersal of the species.

(4)

An alternation of generation between asexual and sexual phases of an organism is referred to as metagenesis.

E.g., in Obelia (a coelenterate), polyps reproduce asexually and medusae reproduce sexually.

(2)

Petromyzon (Lamprey) belongs to the Class Cyclostomata of Phylum Chordata. It is a jawless fish which lays eggs in fresh water. The eggs hatch in about 3 weeks into minute transparent larvae called ammocoetes. After metamorphosis, the young lampreys swim down to the sea where they remain for 3 or 4 years before reaching maturity, when they once again migrate to streams or rivers to spawn and die. Gonads become mature at that time when adults return to rivers for spawning.

(1)

Trichinella spiralis is a minute nematode parasite that shows viviparity i.e., produces live youngs (larvae) not eggs. The adults of T. spiralis live in the human small intestine, where the females release large numbers of larvae. These larvae bore through the intestine and can cause trichinosis or trichiniasis which has symptoms like diarrhoea, nausea, vertigo, pain in limbs and fever etc.

(1)

Duck-billed platypus is an egg-laying mammal. It is found in the rivers in Eastern Australia and Tasmania. It is a beaver-like monotreme about 50–60 cm long and well adapted to live in water. Usually, two eggs are laid at a time. The female curls around them for incubation and remains inactive for about two weeks. Newly hatched young ones are very immature, naked, blind and each is 2.5 cm long.

(1)

Exoskeleton made of cuticle has enabled insects to live on land and to diversify to almost all the possible habitats. It gives them protection, support and also helps to prevent desiccation.

(4)

Cnidarians are the sac-like animals which are aquatic, mostly marine except a few like Hydra, are fresh water forms. They are the simplest organisms that have attained a tissue level of organization. Members of Ctenophora, Cephalochordata and Echinodermata are exclusively marine.

(2)

Planaria possesses high degree of regeneration. Both epimorphosis, in which the missing parts are formed, and morphallaxis, in which the whole body can be regenerated from a fragment of the body.