Question

Medusa of Obelia is
(a)Carnivorous
(b)Herbivorous
(c)Detritus feeder
(d)Omnivorous

Answer 1

Hint: Obelia is a marine animal that belongs to the phylum Cnidaria. It has two reproductive stages in its life cycle known as polyps and medusa. Polyps are the asexual reproductive phase whereas medusa is the sexual reproductive phase.

Complete answer:
Obelia belongs to the genus hydrozoans which is a class consisting of mainly marine and some freshwater animal species which exist in both polyps and medusa stages in their life cycle. Members of hydrozoa are relatively simple in structure. Obelia is commonly known as sea fur. Obelia shows alternation of a generation which means that there is an alternation between polyps and medusa stage. The asexual polyp stage of Obelia eats aquatic crustaceans and worms. Whereas the sexual medusa stage feeds on planktons. So both the polyp and medusa stage of Obelia are carnivorous in nature.

Additional Information: Let us know more about the phylum Cnidaria.
-It consists of organisms that are aquatic, sessile, or free-swimming and readily symmetrical.
-Tissue level of organization and a diploblastic body is present in them.
-They are called cnidarians as they have cnidoblasts or cnidocytes present on the tentacles of their body.
-Cnidoblasts have nematocysts (stinging capsules) and thus are used for anchorage, defense, and capture of prey.
-Another characteristic feature is the presence of a large central gastro-vascular cavity with a single opening known as hypostome.
-The sessile cylindrical form is known as a polyp and is seen in Hydra, Adamsia, etc
-The umbrella-shaped free-swimming form is known as medusa and is seen in Aurelia and jellyfish.
-Examples of cnidarians include Physalia which is known as the Portuguese man-of-war, Adamsia known as the sea anemone, etc.
So, the correct option is ‘Carnivorous’.

Note: -Obelia consists of an outer epidermis (ectoderm) and an inner gastrodermis (endoderm).
-There is a jelly-like matter present between these two layers known as mesoglea.
-Digestion is both extracellular as well as intracellular in cnidarians.

Diagram: An example of a Cnidarian: Jellyfish