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Which of the following is an animal that remains fixed in one place?
A. Amoeba
B. Sponge
C. Chlamydomonas
D. Hydra

Last updated date: 22nd Feb 2024
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IVSAT 2024
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Hint: Animals that are fixed in one place and do not move from one location to another are known as sessile animals. Animals that belong to the phylum porifera are all sessile. These animals remain attached to a substratum throughout their lives.

Complete answer: In Amoeba, member of the phylum protozoa. It belongs to the class Sarcodina. It is a unicellular organism. Amoeba moves with the help of pseudopodia. Pseudopodia is the extended plasmalemma.
-In Sponge, a member of the phylum Porifera. The members of this phylum are sessile animals. These animals cannot locomote to different places. They remain attached to a surface throughout their lives. They do not have any organs for locomotion as well.
-Chlamydomonas is a member of the phylum algae of the kingdom Plantae. Chlamydomonas is a member of the class Chlorophyceae or green algae. It is a unicellular organism. Chlamydomonas has a pear-shaped body and two flagella. The flagella help the algae to swim and move from one place to another.
-Hydra is a member of the phylum Cnidaria. These animals move with the help of tentacles. The tentacles are thread-like structures that move and capture the prey for the hydra. Also, the tentacles possess the cnidoblast cells or the nematoblast cells to protect itself from the prey.
Thus, based on the above information we can conclude that the sponge is an animal that remains fixed in one place.
Hence, the correct answer out of the provided choices is option (B).

Note: Poriferans were earlier considered as plants. This is because they were attached to the substratum and they could not move, and it was believed that animals could move and plants remained attached to the surface. However, later Elis found the water circulation in the Poriferans and classified them as animals.