Green gland in Crustaceans

• Green gland:-
In decapod crustaceans excretory organs are known as antennary gland or green gland. These glands are opaque-white, pea seed sized structures, enclosed in the coxa of each 2nd antenna.
Each organ consists of 3 parts: 1. End sac 2. Labyrinth or glandular plexus 3. Bladder.
1. End sac:-
 This is a small, bean-shaped structure containing a large blood lacuna.
The wall of the end sac consists of 2 layers-
The outer thick layer consists of connective tissue containing numerous, minute blood lacunae.
The inner thin layer consists of excretory cells having excretory function.
 The wall of the end sac is produced into a number of radial septa, projecting into the central cavity.
2. Labyrinth or glandular plexus:-
 It lies on the outer side of the end sac.
It consists of numerous, narrow, branched & coiled excretory tubules, embedded in a mass of connective tissue with blood lacuna.
The wall of each tubule consists of a single layer of excretory epithelial cells.
The tubules open by a single aperture into end sac & by many apertures into the bladder.
3. Bladder:-
The bladder is the largest part of green gland.
It is a thin walled sac with an epithelial lining.
It communicates with the exterior through a small ureter which opens to the outside by a small rounded renal aperture, present on the base of each 2nd antenna.


• Functional aspect:-
The end sacs excrete mainly compounds of NH3 but uric acid & other nitrogenous compounds are excreted by other parts.
The excretory fluid from end sacs pass into labyrinths.
The greatly folded, glandular labyrinth is the site for selective resorption.
The remaining fluid (urine) passes into the bladders & finally expelled out through renal apertures.
         Therefore the green gland extract nitrogenous wastes as well as maintains ionic & water balance.