Nervous system and Respiratory system of Unio.

Nervous system of the Unio.

Unio has a muscular body performing coordinates movement, but the nervous system is greatly reduced due to the extent because of the sedentary and sluggish mode of life.It consists of

(i) central nervous system, including three pairs of ganglia,

(ii) their connectives and

(iii) Commissures.There is a little evidence of a brain.

However, the various ganglia, their connectives and the commissures are as follows.

(i) Cerebro-pleural Ganglia.

At the base of the labial palps, just outside the corners of the mouth on either side, is placed a small yellowish, somewhat triangular paired cerebro-pedal ganglion, about the size of the head of a pin.Each cerebro-pleural ganglion is formed by the fusion of the cerebral ganglion and a pleural ganglion.The ganglion of the both of the side is equivalent to the brain. They are connected with each other by a thin transverse cerebral commissures, which passes over the oesophagus. Each Cerebro-pedal Ganglia give out.

(i) an anterior adductor nerve to the corresponding muscle,

(ii) a labial nerve to the labial palp, and

(iii) an anterior pallial nerve to the anterior part of the mantle.

Besides this ganglia gives off two conspicuous connectives

,(i) a cerebro-visceral connective which run posteriorly to unite, with the visceral ganglion of that side, and

(ii) cerebro-pedal connectives which pass ventrally into the foot to unite with the pedal ganglion of the same side.

(ii) Pedal ganglion.

These are also called paired ganglion.The pedal ganglion lies in the foot, about one-third distance from its anterior end, dorsal to its muscular portion and just below the visceral mass. The two pedal ganglion are closely united to form a bilobed mass. The pedal ganglion supply to the foot, its muscle and statocyst.Each pedal ganglion is connected to the cerebro-pleural ganglion of its side by the cerebro-pedal connective.

(iii) Visceral ganglion.

These are paired ganglion. The two visceral ganglia situated mid-ventrally upon the posterior adductor muscle.These ganglia are fused together to form a flattened x-shaped mass. The visceral ganglia give out (i) a dorsal nerve papillae, (ii) a posterior pallial nerve to the posterior part of the mantle, (iii) a posterior renal nerve to the kidney, (iv) a branchial nerve to the gill, and (v) a posterior adductor nerve to the corresponding muscle.Besides, it is connected with the cerebro-pleural ganglion of each side by a long , thin cerebro-visceral connectives, which runs forward through the substance of kidney just below the place of attachment of the gill lamina, giving off several small nerves to the visceral mass on its way.

(iv) Commissure.

The cerebro-pleural ganglia of both the sides are connected together by a thin, transverse, loop-like nerve passing over the oesophagus; this nerve is called cerebral commissure. No other commissures are found in Unio.

(v) Connectives.

All these connectives are paired. However, there is no connection between the pedal and visceral ganglia. All these three ganglia are connected with somewhat stout nerves representing the connectives; the cerebro-pleural is connected to pedal by cerebro-pedal connectives, cerebro-visceral connected to visceral by cerebro-visceral connectives.

Reproductive system of Unio

Unio is dioecious,i.e., the sexes are separate but there is no sexual dimorphism.

Gonads.

The gonads, testes in male and ovaries in a female, are a pair of large, simple, branching tubes, lying among the intestinal coils, in the visceral mass, just above the foot.During the breeding season, they become greatly enlarged and conspicuous; the testes are brightly whitish and ovaries are reddish. The lining of the gonads proliferates to give spermatozoa in male and eggs in the female. Each gonad has a short duct, vas deferens in male and oviduct in the female, opening into the suprabranchial chamber of the mantle cavity near the excretory pore. Accessory reproductive structures are not found in bivalves.There are no accessory reproductive organs like gonads and the copulatory structures.

Reference.

Agrawal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L.,Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

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