Question

12. Name some representatives of the Phylum Coelenterata.

13. Describe the role of the nematocyst.

14. Mention how gas exchange and excretion occur in coelenterates.

15. Describe the meaning of the term polymorphism and mention some examples.

  16. What are some examples from the Hydrozoa class?

Answer 1

Some representative of coelenterata-

• Jelly fish (Chrysaora melanaster)
• gorgonian (Annella mollis)
• rocky coral (Acropora cervicornis)
• sea anemone (Nemanthus annamensis)

Role of nematocyst-

Nematocyst helps the animal to attack their predators.It is a small stinging cells that are located on the tentacles of jellyfish.

Nematocysts inject venom into prey, and usually have barbs to keep them embedded in the victims.

Gas exchange and excretion-

In Coelenterata gas exchange takes place through water being pumped in and out of the gastrovascular cavity. Oxygen & other nutrients passes over the cells and in exchange cells excrete their waste materials. Gas exchange and circulation in Cnidaria occurs via diffusion.

Polymorphism-

Polymorphism refers to the phenom­enon of existence of different physiological and morphological forms represented by an extensive range of variation within a single species.

In Cnidarians there are particularly two types of form- medusa & polyp.

Polymorphism present in Hydrozoa​​​​​.

Polyp form:

(i) Sedentary tubular form with one end closed.

(ii) Free conical end (preoral end) bear­ing hypostome, mouth and tentacles.

(iii) Aboral end fixed.

(iv) Mouth situated on hypostome lead­ing to coelenteron.

(v) Un-branched elongated tentacles sur­rounding the mouth.

(vi) The polyp may be encased by a trans­parent covering, the hydrotheca (e.g., Hydra).

Medusoid form:

(i) Umbrella-shaped with convex exumbrella and ventral concave subumbrellar surface.

(ii) Subumbrellar surface with mouth and manubrium.

(iii) Radial and circular canals present.

(iv) Marginal tentacles are present.

(v) Presence of gonads.

(vi) A velum is often present.

Figure: A) Polyp B) Medusa.