Question

Choose the correct answers from the alternatives given.
Which of the following characteristics is shared by protostomes and deuterostomes?
A. They both have spiral cleavage of the embryo.
B. Coelom develops in the same way in both.
C. Mouth forms first in both, before the anus.
D. They both form a hollow sphere in the embryo that has an indentation called a blastopore.

Answer 1

If the blastopore changes to form the anus during the embryonic development of metazoans they are called deuterostomes. But if the primary cavity turns into a mouth, then those animals are called protostomes.

Complete Answer:
Metazoan animals are classified into two categories based on their embryonic development into protostomes and deuterostomes. During the embryonic development of deuterostomes, radial cleavage or cell division occurs. The cavity formed by the blastopore changes to anus of the organism and the mouth is formed on the opposite side of anus.

Following are the clades of deuterostomes based on the similarities of structure:
1. Echinodermata - Marine animals with radial symmetry. For eg. Sea cucumber and starfish.
2. Chordates - Terrestrial and marine animals such as frog, tiger, bat, snake etc.
3. Cephalochordates - Small marine organisms with a segmented body. Eg. Lancelets.
4. Vertebrates - animals having notochord at some stage of their life cycle. For eg. humans,birds etc.
5. Hemichordates - Marine organisms like echinoderms. For eg. Acorn worm, Pterobranchia etc.

Lower animals where formation of mouth occurs before the formation of anus during embryonic development are called deuterostomes. Mouth is formed from blastopore instead of anus. These animals have simple body structures. The cleavage in deuterostomes was radical whereas in protostomes, it is spiral. Most common examples include - Arthropods, Flatworms, Annelids etc.

So, the correct answer is option (D).

Note: The cleavage in both the groups of animals is different as in protostomes they show radial cleavage whereas in deuterostomes they show spiral cleavage. The coelomic development in both the groups is different. In protostomes, we can see schizocoelom and in deuterostomes, we can find enterocoelom. The development of mouth and anus is the main difference between both the groups.