Nervous system of Freshwater prawn.

Nervous system of the Freshwater Prawn.

The nervous system present in Prawn is of annelidan type, and these are somewhat triangular and are lined by more fusion of ganglia. It consists of four different types of ganglia. They are 1. Central nerve system including brain connected with a

They are

1. Central nerve system including brain connected with a ventral ganglionated nerve cord through a pair of circum-oesophageal commissures,

2. The peripheral nervous system including nerve,

3. Ventral thoracic ganglion mass,

4. Sympathetic nervous system

1. Brain or Supra-oesophageal ganglia. It consists of brain lies at the base of the rostrum, anterior to the oesophagus and surrounded by the thick mass of fat. They are formed by the fusion of the several nerves on each side of supra-oesophageal ganglion following nerves are concerned. It is a bilobed structure.On each side, they give off different types of nerve. (i) Antennulary nerve. (ii) Antennary nerve. (iii) Optic nerve.

(iv) Statocysts nerve. (v) Tegumental nerve.

(vi) Ophthalmic nerve.

(i) Antennulary nerve. It is associated with the brain to antennules.It sends a statocyst branch to the statocyst. (ii) Antennary nerve. It is associated with the brain to

(ii) Antennary nerve. It is associated with the brain to an antenna.

(iii) Optic nerve. It is associated with the brain to eyes

. (iv) Statocysts nerve. It is associated with the brain to the statocyst.

(v) Teguments nerve. It is associated with cephalic appendages/labrum.

(vi) Ophthalmic nerve. It is associated with the eye stalk.

2. Circum-oesophageal commissures.

Posteriorly, the brain gives off a pair off of stout nerves or the circumesophageal commissures, and they run backwards and downward, encircle the oesophagus and they unite ventrally to form sub-oesophagus ganglia. Two commissure are crossed over and form the double bridge of connectives tissue is called endosternite. The commissures arise from the commissural ganglion. A mandibular and transverse nerve arises from it. Both of the oesophagus.

3. Ventral thoracic ganglion.

It consists of thoracic nerves formed by a fusion of 11 pairs of nerves lies mid-ventrally below the cephalic appendages or cephalic nerve. The first 3 pairs are cephalic nerves supply mandibles, and maxillulae and maxilla and last 8 pairs are thoracic nerves concerned with millipedes.

4. Ventral nerve cord.

It emerges from the hind end of stout ventral or abdominal nerve cord.It runs along the midventral line of the abdominal segment which enlarge to form an abdominal ganglion. The ganglia give off three pairs of nerves. i,e Each of pair of pedal nerve, the nerve to extensor muscle, and nerve to the flexor muscle of succeeding segment. The last, sixth abdominal ganglion assumed to be the largest ganglia which are composed of several fused ganglia which consist 2 pairs of a nerve of flexor muscle, 2 pairs of uropods, two pairs of telson and a single median nerve to hindgut.

5. Sympathetic nervous system.

Sympathetic, visceral or autonomic nervous system comprises a few ganglion and nerve. A small, nerve, arising mid-posteriorly from a brain, bears two visceral ganglia lying one one behind the other.The first ganglion is joined with the two commissural ganglia by connectives. Second ganglia give off two pairs of nerves to the wall of the oesophagus and the cardiac stomach.

Body wall of Palaemon.

The body wall of Palaemon consists of three parts.i,e outer cuticle, middle epidermis and inner dermis.

1. Cuticle.

The outer layer of cuticle forming the exoskeleton. It is thick and non-ciliated.It is further divided into a thin non-chitinous outer epicuticle, and a thick, chitinous, and inner endocuticle.

Epicuticle is made up of an outer lipoid layer and an inner protein layer.The lipoid layer is permeable to gases but impermeable to water but the protein layer is relatively thick, hard and is pigmented.It is secreted by the tegumental glands lying in the dermis.Epicuticle is produced into spines of varying forms and bears, at the place, fringes of setae.

They are elastic, permeable, to gases, some solutes and are secreted by epidermis cells. Endocuticle is divided into three successive layers a pigmented layer, a calcified layer and an uncalcified layer. All these layers are made of up chitin. The hole cuticle forms an external supporting structure of the body.The pigmented layer imparts a characteristic colour to the body due to the characteristic colour of the body due to the pigments present in the chromatophore. This chromotophere is also divided into a primary chromatophore located deeper in the body and secondary chromatophores which impart a particular colour to the animal.

2.Epidermis.

They are composed of a single layer of the glandular columnar epithelium with centrally placed nuclei.Epidermis is lined by the thin basement membrane. This layer secretes the overlying endocuticle.

3. Dermis.

It is made up of loose connective tissue beset with blood lacunae. The dermis contains three types of tegumental glands, each of which opens to the outside through fine ducts.

Reference.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

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