Question

A colonial hydrozoan is
A. Aurelia
B. Hydra
C. Metridium
D. Obelia

Answer 1

Hint:-Hydrozoans belong to phylum cnidaria, where they are individuals with small predatory animals, where some live a solitary life and some live a colonial life, and most of them are living in saltwater, and very few genera of hydrozoans are living in freshwater habitats.

Complete answer:
1. Hydrozoans which are solitary are capable of living as an individual, while the one living in colonies, they are larger, it is difficult to separate and live individually.
2. Hydrozoans colonies are called dioecious, which means that they have separate sexes, which includes polypoid and Medusoid stage.
3. When coming to hydrozoans which have polypoids are called polyps, and they generally live in colonies, with multiple polyps connected by a tube-like structure.
4. The tube is a hollow cavity, where it extends in the middle of the polyp so that all other individuals of the colonies are intimately connected.
5. All colonial hydrozoans also include some polyps which are specialized for reproduction.
6. Another type of hydrozoans is Medusa, which is smaller than that of typical jellyfish, that range from 0.5 to 6 cm.
7. Where the colony has polyps, all of them may be either male or female because both sexes are not present in the same colony.
8. Some reproductive polyps are known as gonozooids which bud off, and reproduce asexually and produce Medusa.
9. Some of the examples of colonial hydrozoans are Siphonophores, and obelia, etc.
So, the correct option is D.

Note:- In hydrozoans with polyp and medusa generation, the medusa phase is sexually reproductive, and Medusa of this species of hydrozoans are called as hydromedusae, and this have less lifespan compared to remaining ones.