Question

…………………………………….are non-motile animals.
A) Porifera
B) Coelenterate
C) Mollusca
D) None of these.

Answer 1

Hint: Movement is an important biological activity in living organisms. Except for plants, most of the organisms show movement as an act of moving independently.

Complete answer:
Porifera are marine, multicellular organisms which bear pores and challenges on their body surfaces which allows water to circulate past them. They are non-motile and form sedentary colonies. Porifera consists of jelly like mesophyll or mesophyll cells present in between the two layers of the dermis. Poriferans are commonly called sponges. The poriferans are the lowest multicellular organisms and they belong to the kingdom Animalia.
Coelenterate includes the sea anemones, sea pens, coral animals belonging to the phylum Cnidaria and Ctenophora. They have a very simple type of organization of tissue system. The tissue system consists of only two layers of cells and is divided into the external or internal layer of cells. They show radial symmetry and are solitary in nature. They are motile organisms and lack a specialized circulatory system which works on the diffusion across the tissue layers.
Mollusca are the phylum consisting of organisms bearing a mantle cavity which may or may not cover the body. They are also known as shelled animals and the shell or mantle is made up of proteins and calcium carbonate. The whole body of the organisms can be retracted inside the shell to protect it as the body is quite soft. Molluscs also bear a singular muscular foot, which is used for movement.

>Hence, the option (A) is the correct answer or option.

Additional information
There are about five thousand species of porifera. They are commonly known as the pore bearing multicellular animals. The pores in porifera are known as Ostia. They are exclusively aquatic and are mostly found in marine habitats and only a very few are found in freshwaters

Note: Lower animals are also known as non-chordate or invertebrate. Non chordates are characterised by absence of notochord, skeleton or vertebrate and they are pseudocoelomate or coelomate, triploblastic organisms. Porifera, Coelenterate and Molluscs belong to non-chordates among which Porifera are sedentary and non-motile organisms.