Question

Ladder like nervous system is characteristic of which phylum.
a) Annelida
b) Platyhelminthes
c) Mollusca
d) Chordata

Answer 1

Hint: Phylums have different kinds of nervous systems which are complex in animals as they coordinate in actions and sensory information by signal transduction to different parts of the body. It detects the impacts which are being detected from the environmental change. CNS and PNS belong to the nervous system only.

Complete answer:
b) Platyhelminthes- Platyhelminthes have a ladder-like nervous system with a ventral nerve cord.
Option B is the correct answer.
a) Annelida- annelids have primitive brain and nerve cords which are connected to ventral and anterior ganglia and segments. leeches belong to Hirudinea which is a subclass of Annelida. They are closely related to Oligochaetes.
Option A is not the correct answer.
c) Mollusca- Mollusca have three pairs of ganglia like- cerebral, pedal and pleural ganglia, which are connected to cerebra-pedal and pleuro-pedal. There are diverse animals in this group which are an important part of the ecosystem.
Option C is not the correct answer.
d) Chordata- Chordata have hollow nerve tubes and notochords which are in expanded tubes and vesicles.
Option D is not the correct answer.

Note:
Flatworms also known as Platyhelminthes have complex yet decentralized nervous systems. It is longitudinal having peripheral nerve plexuses and auricles too. The nerves are connecting the cords from the side of the head. Due to their cylindrical body their nervous system is ladder-like.