RESPIRATORY SYSTEM OF PRAWN

Palaemon is a fresh water Prawn. It performs respiration by 3 organs.

1. Gills or Branchiae

2. Epipodites

3. Lining of branchiostegites

1. Gills or Branchiae :

1. There are eight pairs of gills.
2. They show semi-lunar shape.
3. They are arranged vertically one, behind the other in a row.
4. The third pair of gills are the smallest.
5. The gills are attached by their middle part to the body, which is called root.

According to their attachment three types of gills are seen in Palaemon.

i) Podo branches : The gills are attached to podomere.

Ex : The first pair of gills are attached to the coxae of the second maxiiii pedes.

ii) Arthro branches : These are attached to the arthrodial membrane which concects the appendage to the body.

Ex : The second and third pairs of gills are attached to the arthrodial membrane joining a limb with the body.

iii)Pleuro branch: The gills are attached to the lateral walls of the body.

Ex.- In Palaemon 5 pairs of gills are attached to the lateral walls of the thorax, one above each walking leg.

Structure of gill:

1. A gill consists of a narrow 'vertical axis' with two rows of thin "gill plates".
2.  The gill plates of each row are arranged like the leaves of a book.
3. Such gills are called phyDobranches.

1. Axis and Blood Supply:

1. The axis of the gill contains a central core of connective tissue.
2. It has three longitudinal blood channels. Two are lateral longitudinal channels.
3. The third one extends beneath are groove between the rows of gill plates and is called median longitudinal channel.
4. The lateral longitudinal channels are connected together at intervals by transverse channels.
5. The transverse channel present opposite to the root of the gill receives the afferent braftchial channel which brings deoxygenated blood from the body.
6. Each lateral channel gives off a slender marginal channel to each gill plate of its side.
7. It opens into the median longitudinal channel.
8. The median longitudinal channel gives of the efferent branchial channel that carries oxygenated blood to the pericardial sinus and the heart.

2. Gill Plate:

1. It is made by a single layer of cells.
2. A marginal blood channel is present in it.
3. The gill plate is covered by cuticle.

Working:

1. The balers [Scaphognathites] by their movement produce a constant current of water which passes through the gill chambers.
2. The current Of water enters the gill chambers from behind and passes upwards and leaves at the anterior end.
3. The lining of the gill plate has very thin cuticle which contains blood.
4. Therefore, the oxygen of the water diffuses into the blood and C0₂ from blood diffuses into the water.
5. The oxygenated blood returns to the heart is and supplied to the body parts.

2. Epipodites:

1. Three pairs of epipodites are present.
2. They are present in the anterior part of the gill chamber.
3. They are thin and leaf-like.
4. They are the outgrowths of integument of the coxae of the maxilhpedes.
5. The first pair of epipodites are larger and bi lobed.
6. The epipodites regarded as simple gills. They are supplied with blood.
7. They are in contact with water.
8. They take up respiratory function.

3. Lining of Branchlostegites :

1. The inner fining branchlostegites is thin. It contains blood lacunae.
2. It is in contact with fresh water.
3. Because of which lining of branchiostegite is respiratory in function.