Question

An animal with metameric segmentation (metamerism) is:
A. Housefly
B. Earthworm
C. Roundworm
D. Planaria

Answer 1

Metameric segmentation is true segmentation in which external segmentation corresponds to the internal segmentation, this dividing the body into a number of linear series of segments (metameres). It is mainly found in phylum Annelida and also in members of Arthropoda.

Complete answer:
A. Housefly: It belongs to class Insecta, of phylum Arthropoda. These do not have a metamerically segmented body. Option (a) is incorrect.

B. Earthworm: It belongs to class Oligochaeta of the phylum Annelida. As mentioned earlier, true metamerism is the characteristic of annelids. Earthworms have 100-120 meters. Option (b) is correct.

C. Roundworm: These are Aschelminths or Nematodes and these do not possess metameric segmentation. Option (c) is incorrect.

D. Planaria: It belongs to class Turbularia, of phylum Platyhelminthes and is not a segmented organism. Though it has a high power of regeneration. Option (d) is incorrect.

Hence, the correct answer is (b).

Note: Other common features of phylum Annelida:
- They are bilaterally symmetrical and triploblastic animals.
- These are protostomes (blastopore converts first into mouth).
- Coelomates i.e., true coelom is present in them. They are schizocoelomate, meaning the coelom is formed through a fischer in mesoderm.