Question

Which animal possesses the most primitive nervous system?

• A. Earthworm
• B. Hydra
• C. Frog
• D. Human

Hint:

The simplest nervous system in animals is the nerve net, found in Cnidarians such as Hydra and jellyfish. It lacks a central brain and allows impulses to move in different directions.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the organism with the simplest or earliest form of a nervous system among the given choices. In biological evolution, the nervous system began as simple networks before developing into complex centralized organs.
Step 2: Detailed Explanation:
In the animal kingdom, members of the phylum Cnidaria (such as Hydra) are the first to exhibit a nervous system.
Unlike higher animals, Hydra does not have a brain or a central nervous cord. Instead, it possesses a "nerve net."
This nerve net consists of interconnected neurons spread throughout the body wall.
While organisms like Earthworms have ganglia (primitive brains), and Frogs or Humans have highly centralized systems with brains and spinal cords, the Hydra's system remains the most basic and decentralized.
Step 3: Final Answer:
Hydra possesses the most primitive nervous system, characterized as a diffuse nerve net.