31 Years NEET Previous Year Questions: Animal Kingdom - 1

Cnidarians are aquatic, mostly marine, solitary or colonial sessile or free-swimming radially symmetry animals while members of Ctenophora, Cephalochordata, Echinodermata are found exclusively in the marine environment.
So the correct answer is 'Cnidaria'.

Gorgonia (sea-fan) is an animal and all animals lacks a cell wall.

• Planaria is a flatworm that possesses a high power of regeneration due to the neoplastic cells which are found in them.
• If an individual is cut transversely into two parts, the anterior segment will generate a new tail and the posterior end will develop a new head.

Torpedo is a sluggish fish. It is carnivorous. The prey is firstly killed by electric shock. The shock can also be harmful to human beings.

Platypus is an oviparous animal (egg-laying). It belongs to the class- Mammalia.

• Cyclostomata have sucking and circular mouth without jaws. Median fins (appendages) are present but paired fins (appendages) are absent. Integuments are without scales.
•  In aves, forelimbs are modified into wings for flying and hind limbs are used for walking and running. The body is covered with feathers. Skin is thin, dry and non-glandular. Lungs have air sacs. 
• In mammals, mammary glands are present for the nourishment of the young ones. Hairs are present on the body. They have 2 pairs of limbs. Pinnae are absent in monotreme (mammals that lay eggs). 
• Chondrichthyes have a persistent notochord, placoid scales as the exoskeleton and ventrally positioned mouth. Gill slits are not covered by an operculum. 

• Petromyzon (Lamprey) 
  Class: Cyclostomata 
  Phylum: Chordata
• It is a jawless fish that lays eggs in freshwater. 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.

• Phylum Porifera (the sponges) has a cellular level of body organisation, with an 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.

• Parapodia are present in aquatic annelids like Nereis, which help them in swimming.
• The other three features, i.e. metameric segmentation, jointed appendages and chitinous exoskeleton are present in phylum-Arthropoda. 

• Chondrichthyes always have a cartilaginous endoskeleton.
• Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas lay eggs.
• Chordates have jawless animals (Agnatha) as well.
• Most reptiles have 3 chambered heart. Crocodilians have 4 chambered hearts. Turtles have 3 chambered heart but with an incomplete wall in the single ventricle, so their hearts are functionally 4 chambered.

• Giving birth to living young that develop within the mother's body rather than hatching from eggs is called viviparity.
• All mammals except the monotremes are viviparous. Birds are oviparous and mammals are viviparous.