Question

3. Add a small piece of egg yolk to the water near mall piece of egg yolk to the water near the planarian. The planarian may approach the egg und begin to feed by extending a long tubular pharynx out of the mouth, a circular opening on the ventral side of the body. Record your observations in the questions below. Observe the prepared slide of the planarium cs under the compound microscope. + Review of Phylum Platyhelminthes: 1. What class of Platyhelminthes does the planarian belong to? 2. What are some of the distinguishing characteristics of organisms in Phylum Platyhelminthes? 3. Describe the locomotion of the living planarian observed in class. Is the locomotion directional what is the position of the head? Does its body appear to contract? 4. How does the symmetry of the planarian differ from those exhibited by the Porifera and the Cnidarians? Why is the planarian considered to be the most evolutionarily advanced of the three phyla already studied?

Answer 1

Ans-1 Planaria belongs to the class Turbellaria of Phylum platyhelminthes. In this class , free living flatworms are present which could be freshwater or terrestrial ones.

Ans-2 Distinguishing characteristics of Phylum platyhelminthes.-

• they are acoelomate animals means no coelom.

• they are dorsoventrally flattened or leaf like structure.

• could be free living or parasitic

• bilateral symmetry is present in these organisms

• they have undergone cephalization( means they have head)

• they have a ladder like nervous system with no spinal cord

• they have three germ layers ( means triploblastic)

Ans- 3 The locomotion of Planaria is directional because of the presence of cephalization. They usually glides over the surface by beating their epidermal cilia. They have longitudinal, circular and oblique muscles and while gliding over the surface, they show contraction in circular muscles which is not properly visible but yes they do show contractions.

Ans- porifera are unsymmetrical and cnidaria are radially symmetrical while platyhelminthes are bilateral symmetrical. Animals in phylum cnidaria and porifera cannot be divided into identical equal halves like that in platyhelminthes. It is considered most evolutionary advanced among the three phyla because it is the first phylum to show presence of cephalization which means a initiation of nervous system in the animals. This is major advancement because earlier animals don't have any such evolved characters that could help them to react in a certain specific way. There response towards stimuli have also shown their advancement from animals of earlier two phylums.

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