1. Gills or Branchiae
3. Lining of branchiostegites
1. Gills or Branchiae:
- There are eight pairs of gills.
- They show semi-lunar shape.
- They are arranged vertically one, behind the other in a row.
- The third pair of gills are the smallest.
- 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:
- A gill consists of a narrow 'vertical axis' with two rows of thin "gill plates".
- The gill plates of each row are arranged like the leaves of a book.
- Such gills are called phyDobranches.
1. Axis and Blood Supply:
- The axis of the gill contains a central core of connective tissue.
- It has three longitudinal blood channels. Two are lateral longitudinal channels.
- The third one extends beneath are groove between the rows of gill plates and is called median longitudinal channel.
- The lateral longitudinal channels are connected together at intervals by transverse channels.
- The transverse channel present opposite to the root of the gill receives the afferent braftchial channel which brings deoxygenated blood from the body.
- Each lateral channel gives off a slender marginal channel to each gill plate of its side.
- It opens into the median longitudinal channel.
- The median longitudinal channel gives of the efferent branchial channel that carries oxygenated blood to the pericardial sinus and the heart.
2. Gill Plate:
- It is made by a single layer of cells.
- A marginal blood channel is present in it.
- The gill plate is covered by cuticle.
- The balers [Scaphognathites] by their movement produce a constant current of water which passes through the gill chambers.
- The current Of water enters the gill chambers from behind and passes upwards and leaves at the anterior end.
- The lining of the gill plate has very thin cuticle which contains blood.
- Therefore, the oxygen of the water diffuses into the blood and CO2 from blood diffuses into the water.
- The oxygenated blood returns to the heart is and supplied to the body parts.
- Three pairs of epipodites are present.
- They are present in the anterior part of the gill chamber.
- They are thin and leaf-like.
- They are the outgrowths of integument of the coxae of the maxilhpedes.
- The first pair of epipodites are larger and bi lobed.
- The epipodites regarded as simple gills. They are supplied with blood.
- They are in contact with water.
- They take up respiratory function.
3. Lining of Branchlostegites:
- The inner fining branchlostegites is thin. It contains blood lacunae.
- It is in contact with fresh water.
- Because of which lining of branchiostegite is respiratory in function.