Question

In metagenesis
A. Polyp produces medusa asexually and medusa produces polyp asexually.
B. Polyps produce medusa sexually and medusa produces polyp asexually.
C. Polyps produce medusa asexually and medusa produces polyp sexually.
D. Polyps produce medusa sexually and medusa produces polyp sexually.

Answer 1

Hint: Metagenesis is a unique process of alteration of the reproductive cycle found in cnidarians. The asexual stage is represented by Polyp and the medusa represents the sexual stage.

Complete answer:
By budding Polyp forms the medusa while the medusa by sexual reproduction forms polyps. A medusa produces gametes (male & females), which are shed into the water; upon fertilization, the structure develops into a swimming larva, which later on settles and develops in a polyp.

So, the correct answer is (C) Polyps produce medusa asexually and medusa produces polyp sexually.

Additional Information:

Polyp	Medusa
They are asexual form	They are sexual form
Body shape- tubular	Body shape- bell-shaped
Mouth direction- upwards	Mouth direction- downwards
Manubrium- absent	Manubrium- present
Sense organs- absent	Sense organs- present like photoreceptor & statocysts are found
Method of reproduction- Asexual	Method of reproduction- Sexual
Evolutionarily they are primitive form of Cnidarians	Evolutionarily they are a more advanced form of Cnidarians
Cleavage- absent	Cleavage- Holoblastic
Fertilization- absent	Fertilization- present

Note:
> Metagenesis is the phenomenon where one generation of certain animals reproduce asexually, while the next generation is sexually reproducing. Both generations of these organisms are diploid during metagenesis, so it represents the alternation of generation.
> Example - Coelenterates like Obelia where polyp alternates with medusa in their life cycle. Medusa possesses gonads. They are dioecious, i.e. sex organs (testes and ovaries) are borne on separate individuals.
> Four gonads are found in each medusa. Gonads are ovoid, knob-like bodies lined by epidermis from outside and by gastrodermis from inside. Fertilization is external. Post gamete liberation parent medusa dies.
> Zygote undergoes holoblastic cleavage, which forms morula, later on, it develops into a blastula.
> Blastula consists of blastomeres & bears a cavity called the blastocoel.
> Gastrula in this case is stereo gastrula. Gastrula later forms a planula larva that can swim.