Question

Cephalization first occurs in:

• A. annelida
• B. flatworm
• C. roundworm
• D. mammals

Answer 1

The correct option is A

annelida

The correct option is A

Explanation of the correct option:

1. The union of a few of the anterior body segments to form a head which is specialized by the development of nervous, sensory, and feeding structures is called cephalization.
2. Cephalization is due to the development of feeding organs in association with the mouth and the concentration of the principal sense organs.
3. The nervous tissue also becomes concentrated to form a brain in the head.
4. Annelids are the first group of non-chordates that show cephalization.

Explanation of the incorrect option:

Option B:

1. They are triploblastic, acoelomate, bilaterally symmetrical and organ level of organization.
2. Their body is dorsoventrally flattened without any segments and appears like a leaf.
3. They are devoid of the anus and circulatory system but have a mouth.
4. They respire by simple diffusion through the body surface.
5. They do not have a digestive tract.
6. They are hermaphrodites, i.e., both male and female organs are present in the same body.

Option C:

The organisms belonging to the phylum Nematoda are also known as “roundworms”. They are unsegmented vermiform animals.

Option D:

1. Mammals are warm-blooded animals who give birth to their younger ones.
2. They have mammary glands that help them produce milk to feed their younger ones.
3. Presence of a region of the brain known as the Neocortex.
4. Mammals have a four-chambered heart. The sinus venous and renal portal systems are absent.
5. The brain is well developed and divided into the cerebrum, cerebellum, and medulla.
6. The mammals can lay eggs also. They are known as viviparous.

Final answer: Cephalization first occurs in Annelida.