Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.2.14. Nervous System
Freshwater mussel has a muscular body, performing co-ordinated movements; but the nervous system is greatly reduced due to sluggish and sedentary mode of life and there is little evidence of a brain. It consists of—(l) a central nervous system, including three pairs of ganglia for three main regions of body (head, foot and viscera) respectively, (2) their connectives, and (3) small nerves.
Cerebro-pleural ganglia
At the base of the labial palps, just outside the corner of the mouth on either side, is placed a small yellowish, somewhat triangular cerebro-pleural ganglion, about the size of the head of the pin. The ganglia of both the sides are equivalent of the brain. They are connected with each other by a transverse cerebral commissure which passes over the cesoohagus. The cerebro-pleural ganglia supply nerves to the anterior adductor muscle, the labial palps and the anterior region of the mantle lobes. Besides, each ganglion gives off two conspicuous connectives, a cerebro-visceral connective which runs posteriorly to unite with the visceral ganglion of that side, and a cerebro-pedal connective which passes ventrally into the foot to unite with the pedal ganglion of the same side.
Pedal ganglia
The pedal ganglia lie in the foot at the one-third distance from its anterior end, dorsal to its muscular portion and just below the visceral mass. The two pedal ganglia are closely united to form a bibbed mass, which gives off nerves to the foot, its muscles and the statocysts. Each pedal ganglion is connected to the cerebro-pleural ganglion of its side by the cerebro-pedal connective.
Visceral ganglia
The two visceral ganglia situated mid-ventrally upon the posterior adductor muscles, are fused together into a flattened somewhat rectangular mass. On each side, the visceral mass gives off—(l) a dorsal pall/al nerve, a posterior pall ial nerve to the posterior part of the mantle, a posterior renal nerve to the kidney, (4) a branchial nerve to the gill, and (5) posterior adductor nerve to the correspond¬ing muscle. Besides, it is connected with the cerebro-pleural ganglion of each side by a long, thin cerebra-visceral connective, which runs forward through the substance of the kidney just below the place of attachment of the gill lamina, giving off several small nerves to the visceral mass on its way.