Question

Segmentation in the body is first observed in which of the following:
A. Platyhelminthes
B. Aschelminthes
C. Annelida
D. Arthropoda

Answer 1

Hint: Segmentation is a body plan feature observed in animals in which the body is formed from a series of repeating fragments. It is also known as metamerism and each body segment is called a metamere.

Complete Answer:
Let us analyse the options to find the correct answer.
- Option A: Metamerism or segmentation of body is absent in Platyhelminthes. An Example of Platyhelminthes is Tapeworms. Hence, this is an incorrect option. These animals are bilaterally symmetrical and triploblastic.
- Option B: Aschelminthes are non non segmented animals. Roundworms is an example. Hence, this is an incorrect option. They are aquatic and unsegmented worms.
- Option C: Segmentation was first observed in Annelida in the animal kingdom. Segmentation is a fundamental characteristic of Phylum Annelida. Examples include Earthworm and Leeches. Segmentation evolved independently in Annelida and is conspicuous in their adult forms. Hence, this is the correct option.
The segmented body plan implies that the internal and external features of morphology are the same in each body segment. To make their movement more efficient Annelids can add more segments and become bigger.
- Option D: Arthropoda comes after Annelida in the plant kingdom. They have segmentation but it was not observed for the first time in them. Hence, this is an incorrect option.

Hence the correct answer is option C.

Note: With the evolution of segmentation animals were able to perform sophisticated movements and acquire complex body plans. The functions were divided between different parts of the body.