Question

Describe the polymorphism in obelia

Answer 1

Answer:

Because, in Obelia, there are no true two generations to alternate each other. ... Obelia shows polymorphism in which the polyps are for feeding the colony, blastostyles for budding and medusae for disseminating gametes.

Answer 2

Explanation:

What is polymorphism?

Polymorphism = Poly + morphe

(Which implies many forms)

Polymorphism is a distinct characteristic in which a single organism shows more than one different forms which are morphologically and functionally different.

For example: In a group of termites that consists of Queen termites, workers and soilders. All are of same species but the Queen termite is larger in size and lays eggs while others are smaller. Workers can fertilise Queen's ova to form new queen else new workers will be reproduced by parthenogenesis.

Importance:

- Division of labour: each Individual has assigned a work to do instead of a part of the organism.

Patterns of Polymorphism:

1. Dimorphic : Many hydrozoan like obelia, tubularia performs this. They consist of two zooids or individuals.

2. Trimorphic : They consist of three zooids for feeding, reproduction and protection. Example: plumularia

3. Polymorphic : They include more than 3 zooids like for sensory and skeleton in addition. Example: Physalia

POLYMORPHISM IN OBELIA:

As Obelia are dimorphic, they include two forms in their body strcuture. Those are :

1. Polyp Form: (3cm in size)

It's a plant like cylindrical structure (though it's a cnidaria). It has hydrorhiza (for supporting substratum), hydrocaulus, perisarc (rigidity) and coenosarc. Body is covered with epidermis and gastrodermis. Popyps are sessile.

It has two zooids:

A. Gastrozooid: Helps in feeding, it has tentacles by which it catches minute organisms. It consists of hypostome, hydrotheca and mouth.

B. Gonangium/Blastostyle: During full development it releases gonozooids by budding (asexuality). It release Medusa buds which moves out via opening called gonopore.

2. Medusa Form : (1-2 mm in diameter)

The mudusa buds released by gonopore grows in size representing sexual stage of obelia. Medusa are umbrella like structure, mobile, dioecious and free swimming.

It bears tentacles, statocyst (for sensing), mouth, circular and radial canal (for circulation), mouth, manubrium and 4 gonads which are covered by epithelium.

They burst releasing male gametes which reaches female, fertilises the egg forming zygote.

This zygote then develop to embryo which grows into gastrula then planula which in turn perform metagenesis to form a new hydrula polyp.