Different kinds of excretory system in prawn are as follows:
(a) A pair of antennary or green glands
(b) A renal or nephroperitonial sac and
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(c) The integument.
1. Antennary glands:
The coxa of each antenna encloses an opaque white structure of the size of a pea, called green gland. It has three parts, end sac, labyrinth or glandular plexus, and bladder.
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(a) End sac:
It is bean shaped situated in the anterior part of the gland. Its cavity contains a large blood lacuna communicating with labyrinth by an aperture.
The wall of end sac is double layered. Outer thick layer consists of connective tissue containing numerous small blood lacunae, while inner thin layer consists of large excretory epithelial cells.
(b) Labyrinth:
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It lies on the outer side of end sac and comparatively larger than it. It consists of a mass of branched and greatly coiled excretory tubules.
Tubules are lined by a single layer of large excretory epithelial cells. They open by a single aperture into end sac and by many apertures into bladder.
(c) Bladder:
It is the largest of all, lying on the inner side of end sac. It is a thin walled sac and made up of a single layer of excretory epithelial cells.
Its inner wall is prolonged as a short excretory duct or ureter, which opens to outside through a small rounded renal pore, situated on a papilla on the inner surface of coxa of antenna.
A narrow lateral duct runs posteriorly from the bladder of each antennary gland. Lateral ducts of both sides are connected by a transverse connective just in front of the brain. The two ducts run backward along the oesophagus to open into the renal sac.
2. Renal sac:
It is large, thin walled sac, lying above the cardiac stomach, just beneath the carapace and extending posteriorly upto the gonads. Its wall is made of a single layer of flattened excretory epithelial cells.
3. Integument:
With the moulting of chitinous integnment, the nitrogenous products deposited in the integument also get rid of. Thus integnment is believed to be an important excretory organ.
