Question

Which of the following statements is true about planaria?
a) This animal is covered with a hard layer outside.
b) There is no segmentation of its flat body and is mostly free living.
c) The body is made up of two layers.
d) There are holes and segments all over the body.

Answer 1

Hint:-Platyhelminthes is a phylum comprising invertebrate animals. They are flatworms that can live freely or as parasites. Platyhelminthes do not have a body cavity and thus no specialized organs and systems. Planaria belongs to phylum Platyhelminthes.

Complete Answer:-
Planaria belongs to class Turbellaria and phylum Platyhelminthes. The general characteristics of the animals are listed out below:
● Planaria has a soft unsegmented bilaterally symmetrical body.
● Specialized organs and organ systems are absent and these animals have an acoelomate flat body.
● They have three layers – ectoderm, mesoderm and endoderm.
● Planarians are free living and found in both freshwater and marine water.
● A specific characteristic of the planarians is the ability to regenerate lost body parts.
● They have a branched digestive tract with a single opening. Associated structures like mouth, pharynx and intestine are also present.
● Respiration takes place by diffusion.
● Excretory cells are flame cells.
● Reproduction is sexual or asexual.
● Locomotion takes place by beating cilia.
Therefore, we can conclude that planarians are soft bodied organisms, with an unsegmented flat body. The body is bilaterally symmetrical with three layers. They are mostly free-living forms. There are no holes in the body of planaria.
Thus, the right option is B.

Note:- Planaria are flat bodied bilaterally symmetrical organisms. Planarians have soft bodies without any covering and have three layers. They do not have a coelom, that is they are acoelomate and therefore devoid of respiratory and circulatory systems. Planaria is used in research laboratories for research on aging by virtue of their regenerating capacity.