Question

Which of the following represents the nervous system in Mollusca?
(a) A paired nerve cords
(b) A paired nerve cord with the brain and circumpharyngeal connectives
(c) 3- 4 paired ganglia
(d) Primitive brain with a nerve cord

Answer 1

Hint: The nervous system of mollusks is different from other higher- class organisms. They don’t have a brain or nerve cords. Instead, they own certain specialized cell body masses to carry out neural coordination.

Complete step by step answer:
The nervous system in Mollusca is made of 3- 4 paired ganglia. The three paired ganglia are-
- Cerebral ganglia
- Pleural ganglia
- Pedal ganglia
These are connected by three connectives namely the celebropedal, pluropedal, and celebro pleural.
So, the correct answer is ‘3-4 paired ganglia’.

Additional Information: Cerebral ganglia are masses of nerve cell bodies. Although different mollusks have different types of nervous systems, the typical mollusks have 3 paired ganglia connected by connectives or commissures. The connectives are also three in number, that were mentioned in the answer. The peripheral nervous system consists of a pair of ganglia connected by commissure. The pair of parietal ganglia are connected to that.
This is the hypothetical scheme of the nervous system in mollusks. Various modifications have occurred with evolution such as protoneurous condition, streptoneurus condition, simple chiastoneury, and complex chiastoneury. Among these, the protoneurous one is the simplest and closest to the hypothetical model.

Note: Mollusca is one of those phyla in which members don’t have a brain but produces 3- 4 paired ganglia as their nervous system. In the question, there are other types of nervous systems as well. Members of the phylum Annelida have a primitive brain with a ventral nerve cord. A bilobed brain with subpharyngeal ganglion, circum-pharyngeal connectives, and a ventral nerve cord consist of the nervous system of an earthworm (a member of Annelida).