Question:
The most primitive animal with a central nervous system (CNS) located on the ventral side of body is-------.
The most primitive animal with a central nervous system (CNS) located on the ventral side of body is-------.
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Flatworms like Planaria are the first animals with cerebral ganglia and ventral longitudinal nerve cords.
Updated On: Nov 12, 2026
- Hydra
- Planaria
- Sycon
- Scoliodon
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept
Primitive animals differ in how developed their nervous systems are: no nerves, a nerve net, or a true central nervous system.
Step 2: Compare the animals
Sycon is a sponge (Porifera) and has no nerve cells.
Hydra (Cnidaria) has only a diffuse nerve net with no brain or nerve cord.
Scoliodon is a fish, with a dorsal hollow nerve cord, and it is not primitive.
Step 3: Planaria
Flatworms are the first animals to show cephalisation: a pair of cerebral ganglia in the head and two ventral longitudinal nerve cords joined by cross connectives.
Final Answer:
Planaria is the most primitive animal with a ventral central nervous system. \[ \boxed{\text{(B) }\text{Planaria}} \]
Primitive animals differ in how developed their nervous systems are: no nerves, a nerve net, or a true central nervous system.
Step 2: Compare the animals
Sycon is a sponge (Porifera) and has no nerve cells.
Hydra (Cnidaria) has only a diffuse nerve net with no brain or nerve cord.
Scoliodon is a fish, with a dorsal hollow nerve cord, and it is not primitive.
Step 3: Planaria
Flatworms are the first animals to show cephalisation: a pair of cerebral ganglia in the head and two ventral longitudinal nerve cords joined by cross connectives.
Final Answer:
Planaria is the most primitive animal with a ventral central nervous system. \[ \boxed{\text{(B) }\text{Planaria}} \]
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