Excretory system of Freshwater Prawn.

Excretory system of Freshwater prawn.

The excretory system of prawn consists of freshwater prawn consists of an (i) pair of antennary or green glands, (ii) a pair of lateral ducts, (iii) an unpaired renal or nephroperitoneal sac, and (iv) the integument.

True nephridia don't occur.

(i) Antennary glands.

These glands are white in colour . Antennary gland is big as a shape of pea seed. Coxa of each antenna encloses an antennary gland which is opaque.Each antennary glands or green glands includes three parts. They are (a) end sac, (b) Labyrinth, (c) Bladder.

(a) End sac.

End sac is a beam shaped. It is the smallest part lying between the bladder and labyrinth. Internally end sac contains a large central blood-lacuna. The wall of end sac is made up of two layers projects into the central cavity in the form of radial septa.The inner layer is a thin layer consists od large excretory epithelial cells. The outer layer is a thick wall which consists of connective tissue containing numerous small blood-lacunae.

(b) Labyrinth.

Labyrinth or glandular plexus lies on the outer side.It is relatively large than the end sac.Generally, labyrinth consists of numerous narrow, branching and general coiled excretory tubules. They are embedded in a mass of connective tissues, containing blood lacuna. Each tubule is generally enclosed by a single layer of large excretory epithelial cells. Each labyrinth opens by a single aperture into end-sac and by many apertures into the bladder.

(c) Bladder.

The bladder is lying on the inner side of the end sac.It is a largest, thin-walled sac made of a single layer of excretory epithelial cells.it is the largest gland of all the gland. The inner wall is prolonged by a short excretory duct or ureter. Each bladder open to outside through a small rounded renal pore situated on the papilla on the inner surface of coxa of antenna.

2. Lateral ducts.

It runs posteriorly from the bladder of each antennary gland. These ducts of the both side are connected by a transverse connective just in front of the brain. The two lateral ducts run backwards along the oesophagus to open into the renal sac.

3. Renal sac.

Renal sac is a thin-walled sac lying above the cardiac stomach and just beneath the carapace.The renal sac extending posteriorly up to the gonads. Renal sac wall is made of a single layer of flattened excretory epithelial cells.

Physiology of excretion.

The complex nephridia-like antennary glands extract nitrogenous wastes and excess water(osmoregulation) from blood in the same manner as the vertebrate kidneys. The end-sacs excrete mainly compounds of ammonia , but uric acid and other nitrogenous compounds are excreted by others parts. The excretory fluid from end sacs passes into labyrinths in which the useful materials are taken back by blood (selective resorption). The remaining fluid (urine) passes into bladders and finally expelled out through the renal apertures.

4. Integument.

When the non-living chitinous covering or integument is cast off at each moult, deposited on the integument are also expelled. Thus, integument is believed to be an important excretory organ.

Reference.

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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