Question

In which of the following classes, polymorphism is very distinct?
a. Eucestoda
b. Hydrozoa
c. Crinoidea
d. Gastropoda

Answer 1

Hint: Polymorphism is the occurrence of two or more different morphs or forms in the population of a species. It is also referred to as alternative phenotypes. These morphs must occupy the same habitat at the same time and belong to a panmictic population, a population in which the probability that any given male and female is equal for all individuals.

Complete answer:
• Hydrozoa belongs to Coelenterata.
• These are aquatic mostly marine.
• The sedentary or free-swimming forms or solitary or colonial forms exist.
• They are radially or bi-radially symmetrical.
• They exhibit polymorphism. Two main types of structures exist- Polyp and medusa.
• The polyp is a sessile and asexual zooid and Medusa is a sexual and free-swimming zooid.
• Polymorphism is seen in Obelia.
• Obelia possesses three kinds of zooids: Polyps, blasto styles, and medusae. Polyps are considered as the nutritive zooids that provide food to the colony. Blasto Styles- budding zooids and are responsible for giving rise to medusa by budding.
• Medusae- sexual zooids which have testes or ovaries to produce gametes.

Hence, the correct answer is option (B).

Additional information:
Some information regarding other options-
• Eucestoda- It is commonly referred to as tapeworms. The body is flat and ribbon-like. The body is divided into few or many segments rarely divided.
• Crinoidea- These are marine animals and fall in the class Crinoidea. It is one of the classes of the phylum Echinodermata. These include starfish, brittle stars, sea urchins, and sea cucumbers.
• Gastropoda- These are commonly known as snails and slugs. These belong to invertebrates within the phylum Mollusca called Gastropoda.

Note: The term polymorphism refers to the existence of functionally and structurally two or more different types of individuals within the same organism. The polyps and medusa forms are the characteristic forms of zooids found within colonial organisms like those in Hydrozoa. The zooids will perform different tasks.