In this article we will discuss about the Respiration in Prawn:- 1. Respiratory Structures in Prawn 2. Mechanism of Respiration in Prawn.
Respiratory Structures in Prawn:
In Palaemon, three sets of organs help in respiration which are:
(i) Lining of Branchiostegite,
(ii) Epipodites and
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(iii) Gills.
These organs are enclosed within a special chamber, the gill chamber, lying on each side of the cephalothorax. The gill chamber is covered by the lateral extension of carapace called gill-cover or branchiostegite.
The gill chambers can open vertically, anteriorly and posteriorly:
(i) Lining of Branchiostegite:
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Being highly vascularized, the inner lining of the branchiostegite serves as respiratory surface. In this lining, gaseous exchange takes place between the blood lacunae and surrounding water.
(ii) Epipodites:
Three pairs of small, vascularized, leaf-like membranous structures called epipodites are present on the coxal segment of each maxilliped. These organs lie in the anterior part of the gill- chamber and carry out respiratory functions like the primitive gills.
(iii) Gills:
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Gills are primary respiratory organs in prawn. On each lateral side of the cephalothorax and beneath the branchiostegites, there are eight gills, each attached with the thoracic wall by a gill-root. Seven of these eight gills are serially arranged, while the eighth gill remains concealed under the second one on its dorsal side (Fig. 2.57).
The gills are crescent-shaped and their sizes increase gradually from the anterior to the posterior direction (Fig. 2.58). Each gill has a slender axis or base on which double rows of rhomboidal leaf-like gill-plates are arranged like the pages of a book. These types of gills are called phyllobranch.
Histologically, the gill base has three layers — the outer most cuticle the middle epidermis and the inner most connective tissue mass. Each gill-plate consists of mono layer of two types of alternately arranged cells — pigmented and transparent. This cell layer remains covered by cuticle on either side.
According to the position of origin, the gills are of three types:
(i) Podobranch (Greek: podos, foot; branch, gill) — the first gill from anterior side is podo branch which remains attached with the coxa of the second maxillipede.
(ii) Arthro-branch (Greek: Arthros, jointed) — attached with the arthroidal membrane of third maxillipede. Second and eighth gills are arthrobranch.
(iii) Pleuro-branch (Greek: Pleuros, side) — attached with the outer border o