Mammals give birth to young ones and are called viviparous.

Cnidarians possess tentacles.

In Leeches, body cavity is a true coelom, often divided by internal septa.

Porifera – (Pori - holes) - This group includes organisms with holes. These are non-motile animals attached to some solid support under water. There have holes or ‘pores’, all over the body. These lead to a canal system that helps in circulating water throughout the body to bring in food and is helpful in respiration and removal of waste material. 

Amphibians have a three-chambered heart and not four. All other options are correct.

Liver fluke - Belongs to group platyhelminthes. Platyhelminthes is a group of triploblastic animals.

 Elephantiasis refers to a parasitic infection that causes extreme swelling in arms and legs. This disease is caused by filarial worm.

Arthropods possess jointed legs.

Echinodermata - In Greek, ‘echinos’ means 'hedgehog' (skin is not smooth, but is rough with spines) and ‘derma’ means 'skin'. Thus, these are organisms with spines on the skin. These are free-living marine animals. They have peculiar water-driven tube system, which they use for moving around in water, capture and transport of food and respiration (exchange of gases). For example, starfish and sea urchins. 

The number of chambers in the heart depends on the complexity of the body organization. For example, mammals are more complex and therefore, they possess maximum number of chambers in the heart  (four-chambered heart) and fishes have less complex body organization than mammals, so they possess less number of chambers in the heart than found in case of mammals. Piscean - These are fishes. They are exclusively water animals. Their skin is covered with scales/plates. They obtain oxygen dissolved in water by using gills. They are cold-blooded and have two-chambered heart.  

 Whale, the largest mammal, lives in water. Mammals are warm-blooded animals with four-chambered hearts. They have mammary glands for the production of milk to nourish their young ones. Their skin has hair as well as sweat and oil glands. 

Salamander belongs to the phylum Amphibia.

Aves (birds) have outside covering of feathers, and two forelimbs (either of the two front limbs of four-limbed vertebrates) are modified for flight. 

Reason: Vertebrates are

Mollusca: In the animals of this group, there is bilateral symmetry (the left and the right halves of the body are same in design) with little segmentation. The coelom (body cavity) is reduced. They have an open circulatory system (blood does not flow in blood capillaries) and bear kidney-like organs for excretion of waste material. There is a foot, which is used for moving, e.g. unio, chiton, pila, octopus, etc.