Question

Gonads of Obelia occur
A.In hydrocaulist age and indefinite in number
B.Bases of tentacles of Medusa and 8 in number
C.On blast styles and 8 in number
D.On radial canals , oral surface of Medusa and four in number .

Answer 1

Hint: Obelia belongs to Animal Kingdom of Phylum coelenterata . The Phylum is also known as Cnidaria phylum . Phylum coelenterata exhibits a type of body forms called polyp and Medusa . The polyp is the sessile and cylindrical form like hydra , Adamsia etc. Whereas the Medusa form is umbrella shaped and free swimming like jellyfish .

Complete answer:
1.In some of the cnidarians both forms are exhibited that means alternation of generation is present . Alternation of generation is also known as metagenesis . In Alternation of generation polyps produce Medusa asexually and Medusa produce polyp sexually . Example , Obelia
2.As we know Medusa is produced sexually by polyp . Gonads of the sexual reproduction in Obelia are present on the radial canal which is the oral surface of Medusa and are four in number .
3.These gonads are responsible for the sexual reproduction in the Phylum cylinder and also for the dispersion of sperms and ovum in the water by which fusion between this takes place.
4.Cnidarians exhibit tissue level of organisation and are diploblastic animals . Phylum coelenterata have a gastrovascular cavity with a single opening mouth on the hypostome . digestion is both extracellular and intracellular .
Some of the cnidarians also have a skeleton composed of calcium carbonate .

Hence the correct answer is OPTION(D)

Note: Phylum cnidaria is characterized by the presence of cnidoblast . Cnidoblasts are used for Anchorage , defence and for capture of prey . They are also known as nematocysts.