Question

Radial symmetry is often exhibited by animals having
A) One opening of alimentary canal
B) Ciliary mode of feeding
C) Benthos or Sedentary nature
D) None of the above.

Answer 1

Hint:Radial symmetry is a body plan in an organism which divides into 2 similar halves when a plane passes through their central main axis. A radially asymmetric animal has only bottom and top halves and no right or left half.

Complete answer:
Radial symmetry is a characteristic feature of animals like Jellyfish and Sea Anemone of Phylum Cnidaria which are sessile and bottom dwelling. Such an arrangement in animals implies that all parts around the central axis are symmetrical. This allows the organisms to interact with the outside environment from all possible directions.

Let us analyse the options to find the correct answer.
>Option A. One opening of the alimentary canal is seen in organisms like Hydra and Uvula. Hence, this is an incorrect option.
>Option B. Ciliary mode of feeding is observed usually in aquatic invertebrates. Hence, this is an incorrect option.
>Option C. Organisms having radial symmetry are benthos which means they are bottom dwellers. Also, they are attached or seated on a substratum and do not show much activity which means they have a sedentary lifestyle. Hence, this is the correct option.
>Option D. This is an irrelevant and incorrect option.

Additional Information:
In Sea Anemones the mouth opening which is in the centre is surrounded by tentacles. It helps in catching the food and for defense against the predators.
A jellyfish has two phases in its life cycle which are a bottom dwelling polyp and a free swimming medusa.

Thus, the correct answer is Option (C) Benthos or Sedentary nature.

Note:A radial symmetry helps organisms to maintain a stable position, acquire food from all directions and even interact with the environment.Radial symmetry is mainly seen in phylum Cnidaria and Echinodermata.