Excretory system of Unio.Freshwater Mussel.

Excretory system of Unio.

The excretory system consists of

(i) a pair of kidney or organs of Bojanus, and

(ii) the Keber’s organs.

[I] Organ of Bojanus.

The two kidneys or nephridia are often termed as the organs of Bojanus after the name of their discovered.They are situated beneath the floor of the pericardial cavity, one on either side of the vena cava. They are derived from the true coelom. Each kidney is a long, dark, and glandular tube open at the both end. It is a bent itself like a broad U-shaped tube, with the loop posterior, the two end anterior and the two limbs lying parallel and one above the other. The lower arm is a brown, thick-walled, brown-coloured, glandular part of the kidney, the upper arm of the tube is a thin –walled , non-glandular, and ciliated called the urinary bladder or ureter.

Each kidney opens anteriorly at one end into a pericardium by a minute reno-pericardial aperture, and at the other end, it opens by an excretory or renal pore into the suprabranchial chamber of the mantle cavity.The bladder of both the kidneys intercommunicates by an oval aperture.

Physiology of Excretion.

The ventral glandular portion of the kidney extracts guanine and other nitrogenous waste products of metabolism from the coelomic pericardial fluid as well as the blood supplies to the kidney. The wall of the pericardial sinus are also glandular and supposed to secret waste material from the blood into the coelomic cavity.The ciliated cell lining the urinary bladder create outward current carrying the excretory fluid from the glandular part of the kidney to the suprabranchial chamber of the mantle cavity and finally goes out of the body through an exhalant siphon.There occur reabsorption of inorganic salts in the kidney.Kidney also removes large amounts of water to maintain their blood circulation. Therefore, in addition to excretory function, the kidney are osmoregulatory also.

There is also reabsorption of salt in the two kidneys which also serve for maintaining the blood concentration level by removing excessive water from it.

[II] Keber's organ.

It is also known as a pericardial gland. The Keber,s organ or the pericardial gland is situated in front of the pericardium. It is large, reddish-brown, glandular mass, which helps in excretion, discharging waste products into the pericardial waste products into the pericardial cavity to be finally eliminated through the kidney. Nitrogenous waste consists mainly of ammonia and amino compounds, but traces of urea and uric acid have also been found.It is formed from the epithelium of pericardium.

Locomotion of Unio.

The locomotory organ of Unio is chiefly the foot. They are adapted mainly for burrowing. The movement of the foot is affected by the (i) The anterior and posterior retractor muscles and the anterior protractor muscles, which are also called pedal muscles.and (ii) blood vessel. It protrudes between the grasping shell valve and ploughs through the mud or sand, as the case may be.The contraction of the protractor muscle causes the extension of the foot into the mud which causes an influx of the blood into the food cavity resulting in the dilation of the foot tip and anchoring of foot into the mud.Now, the anterior and posterior pairs of retractor muscles contract. This action tends to withdraw the foot, but since its tip is firmly anchoring, the body is pulled forward. In this action, the blood is forced out of the foot which now becomes narrower. The repeated movement of the foot results in a slow progression of the animal.

Body cavity.

The general body of Unio is a haemocoel that is filled with blood or haemolymph.The true coelom is represented only by three small cavities-(i) A single ovoidal chamber, the pericardium, which lies dorsally, containing the heart and a part of the rectum and lined by the coelomic epithelium, (ii) The gonocoels or the cavities by the gonads, (iii) The urocoels or the cavities of the excretory organs.

Reference.

Aggarwal 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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