Question

The phenomenon of polymorphism (presence of two distinct forms- polyp and medusa) is shown in the phylum
A. Porifera
B. Cnidaria
C. Nematoda
D. Mollusca
E. Echinodermata

Answer 1

Hint: Polymorphism is the phenomenon by which different individuals included in the same colony have different forms of existence. It is exhibited by many organisms in the animal kingdom. The different forms may have different functions associated. It is mainly present in the lower phyla in the animal kingdom.

Complete answer:
Polymorphism is exhibited by members of Kingdom Cnidaria. The different forms are polyp and medusa, where polyps are free-swimming or motile and medusa is sessile or stationary. Some species belonging to this phylum can exist in two different forms alternatively. An example of organisms exhibiting polyp form is the Hydra species. Medusa form is exhibited by Jellyfishes which has an umbrella-like shape.

Considering the other given options:
-Phylum Porifera or sponges are included in kingdom Animalia and mainly consist of aquatic organisms, which are multicellular, these organisms do not possess polymorphism. An example of a member organism is Sycon.
-Phylum Nematoda consists of roundworms which are characterized mainly by parasitic organisms. Leeches are the example of organisms present in this kingdom.
-Mollusca is the second largest phylum in Animalia. It consists of both terrestrial and marine animals. Pila or apple snail and octopuses belong to this phylum.
-Echinodermata consists of marine animals. It consists of starfishes and sea urchins.

Thus, the most appropriate answer is B, i.e., polymorphism is exhibited by cnidarians.

Note: When the members of phylum cnidaria, exist by switching between the polyp and medusa forms, the phenomenon is known as alternation of generations. The polyp is the asexual form while medusa is the sexual form. Under phylum cnidaria, class hydrozoa exhibits alternation of generation. This phenomenon is also known as metagenesis.