• Process by which nitrogenous waste produce during metabolism is removed is known as excretion. Some animals such hydra, echinoderms and other may not posses proper excretory organs the reason is quite clear that they are aquatic and it is supposed that nitrogenous material may be diffuse out of there body through their body surface.
  • While in case of other aquatic animal such as prawn and pila there can be well develop excretory organs. Green gland is present in case of prawn which are responsible for excretion while kidney is present in case of pila for filtration and excretion. Both the organisms remove their waste through flitration through blood and later resorption takes place.
  •  In aquatic organism there excretory organs also function to maintain there body fluid.
FIGURE DEPICTING :- Green gland in Prawn


Palaemon malcolmsonii : fresh water prawn

Excretory system of Prawn consist of following parts :-

  1. Integument
  2. Green gland or antennary gland
  3. Pair of lateral ducts
  4. Nephroperitoneal sac


  • Deposited nitrogenous material secreted by body on integument are expelled out during the casting of each moult.
  • Hence it act as essential excretory organ.


Coxa of each antennae enclose an antennary gland. It includes following three parts

  1. End sac
  2. Labyrinth
  3. Bladder

END SAC :-  It is a smallest been shape part lying between bladder and labyrinth. Internally it contains large central lacuna. Its wall is made up of two layers projects into central cavity in the form of radial septa. Outer thick layer of wall consist of connective tissue containing numerous, small blood lacunae, while inner thin layer consist of large excretory epithelial cells.

LABYRINTH :- It is also known as glandular plexus. Which is comparatively larger than end sac. It consist of excretory tubules embedded in mass of connective tissue. Excretory tubules are greatly coiled, narrow and are present in numerous amount. They opens in end sac by single aperture and into the bladder by many aperture.

BLADDER :- It is largest in all present on the inner side of end sac. Made up of single layer of epithelium. Its inner wall is prolonged as short excretory duct or ureter, which opens outside through small rounded renal pore, situated on papilla on the inner surface of coxa of antennae.


  • From each green gland a narrow lateral duct runs posteriorly from bladder. Transverse connective located infront of brain connects lateral ducts from both side. The two ducts runs backward along the oesophagus to open into renal sac.


  • It is a largest thin wall sac lying above the cardiac stomach, just beneath the carapace and extending posteriorly up to gonads.  Epithelial excretory cell of single layer line ups its wall.
FIGURE DEPICTING Dorsal view of excretory organ of Prawn
FIGURE DEPICTING :- Dorsal view of excretory organ of Prawn


  • Green gland extracts nitrogenous waste from the blood similar to the kidney in vertebrates. End sac excretes mainly the compound of ammonia, where as uric acid and other nitrogenous compounds are excreted by other parts.
  • The excretory fluid are taken into the labyrinth in which the useful material are gathered back by blood known as selective resorption. The remaining fluid that is urine is transfer to bladder finally it expelled out from the renal aperture.


Pila : apple snail

Pila posses large kidney which are also known as renal organ or organ of bojanus. It is present only on left side on right it has been modified into gonoduct.

Location – it communicates with exterior on the other hand with pericardial cavity.

It consist of two chamber a right anterior and left posterior.


  • It is approximately an oval organ lies interior to pericardium. It is red in colour. Through the slit like opening near epitaenia it opens into branchial chamber of mantle cavity. On the other hand it communicates with posterior renal chamber through an internal opening. Internal cavity of anterior chamber is very much reduced due to presences of many triangular leave like processes or lamellae, those arising from the roof alternating with those from the floor. Dorsal surface of the chamber is marked by numerous transverse grooves, corresponding to these internal lamellae.
  • Lamellae on the roof are arranged on the either sides of the median longitudinal axis or the efferent renal sinus. Lamellae on the floor are arranged on the either side of a similar median axis, the afferent renal sinus, which is the right branch of the peri-intestinal sinus. It breaks up into numerous branches to supply the lamellae on both the side.


  • It is broad from brownish to grey and hooked shaped chamber, situated behind the anterior anterior renal chamber, in between the rectum on the right and pericardium and the digestive gland on the left. Its larger internal cavity encloses the part of genital duct and few coils of intestine. At one end it communicates with the anterior renal chamber through an aperture, and at the other with the pericardium through elongated slit like reno pericardial aperture, perforating a thin pericardium septum, separating the two afferent and efferent renal vessels profusely branch in the roof of this chamber.
FIGURE DEPICTING Excreting system of Pila
FIGURE DEPICTING :- Excreting system of Pila


  • Blood is supplied to two renal chamber from which nitrogen wastes are separated. From posterior chamber excretory fluid is transferred to the anterior chamber from where it is discharged into mantle cavity through renal aperture. Finally passes out of the body through right muchal lobe along without flowing water. Excretory fluid contains mostly ammonia and some ammonium compound, urea and uric acid.


Asterias: a sea star

  • There is no specialised organ for excretion. Excretory compounds are mainly ammonia, urea and creatine. They diffuse from the body tissue to coelomic fluid where they are engulf by amoeboid coelomocytes. Latter finally pass out of the body through papulae, the  tip of which pinch off to liberate the coelomocytes. Some excretion also takes place by tube feet by diffusion.
  • Some wastes may be excreted by the cells of the pyrolic caeca and leaves the body through anus.


  • Different organisms differ in their structure, physiology and habitat. It is also very well known only on the basis of habitat many of physiology and structure differ among the organism. Here we discuss process of excretion in case of aquatic invertebrates. There are various adaptation for excretion one of the most fascinating adaptation is seen in the case of the Pila. Pila shows an adaptation of water conservation during the terrestrial phase by converting ammonia into the insoluble uric acid. During the aquatic phase Pila excretes ammonia, while during terrestrial phase it excrete uric acid, hence it is both ammonotelic as well as uricotellic.
  • In Prawn it is seen that some of the time integument act as organ of excretion along with green gland. Nitrogenous waste is removed during casting of each moult.

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