It is very simple in star fish and is found in the form of a nerve net. It consists of nerve fibers and a few ganglionic cells, all confined to the body wall except the visceral nerve plexus situated in the gut wall. The different parts of nervous system are following:
1. Superficial or ectoneural nervous system:
It is situated just beneath the epidermis and consists of
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(i) a circumoral nerve ring
(ii) five radial nerves
(iii) subepidermal plexus.
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The circumoral nerve ring lies in the periphery of the peristome. It supplies branches to peristome and oesophagus.
It also gives off 5 radial nerve cords which run along ambulacral groove of each arm. Each nerve cord terminates in a sensory tentacle.
It supplies fibers to the tube feet. The subepidermal plexus is in the form of an elaborate nerve net throughout the body wall.
This nervous system contains both sensory as well as motor fibers. Thus it serves to recieve stimuli and co-ordinate response like the central nervous system.
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2. Deep or hyponeural nervous system:
It consists of
(i) a double circum oral ring and
(ii) 5 pairs of Lang’s nerves which arise from the ring and extend into the arms, one pair in each. It supplies fibers to the muscles of the arm.
The deep nervous system arises from the mesoderm and is primarily motor in function.
3. Aboral or coelomic nervous system:
It is a thin nerve plexus situated in the aboral body wall. It is somewhat thickened to form an anal nerve ring in the central disc and a nerve in each arm.
It is connected with other marginal nerves. This system also originates from mesoderm and is motor in function.
4. Visceral nervous system:
It consists of a well defined nerve plexus situated in the gut wall. It supplies nerves to the gut wall and is connected with visceral receptors.