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

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. 

Flatworms are acoelomates. There is no true internal body cavity or coelom in which well-developed organs can be accommodated. 

Sycon belongs to Porifera, which have pores all over the body. 

This is not a basic feature that is considered while classifying all organisms into a hierarchical classification. Many organisms may not have any similarities except common habitat. Thus, this is the correct answer choice.

Living beings should be categorised on the basis of their body design.

Whittaker described 5 kingdoms of living organisms. They are Monera, Protista, Fungi, Plantae and Animalia.

Warm-blooded animal species can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The only known homeotherms are mammals and birds.

Reason: Coelom is a true internal body cavity between body wall and digestive tract of many animals in which well-developed organs can be accommodated. 

Spongilla belongs to the group porifera. They are commonly known as sponges. The word ‘porifera’ means organisms with holes. These are non-motile animals attached to some solid support under water. They have holes or ‘pores’ all over the body. These lead to a canal system, which helps in circulating water throughout the body to bring in food and oxygen. The members of this phylum lack mouth and anus. 

Amphibians can live both on land as well as in water.

  Presence of water vascular system is not a feature of vertebrates.

There is an outside covering of feathers and two forelimbs are modified for flight.

A flexible rod-like structure that is present in the embryos of all chordates and in the adult forms of certain groups, such as the lancelets and hagfishes. The notochord develops into the spinal column in most vertebrates.

Yes, a kingdom is the highest taxonomic category. For example, Kingdom Monera, Kingdom Protista, etc. Species is the lowest category. For example, Solanum tuberosum, Panthera leo, etc.