Prawn
Handout gives
the details of
1. External
structure of prawn
2. Appendages
of prawn
3. Digestive
system of prawn
External
Structure:
Prawn
is common in ponds, rivers and fresh water areas. It is omnivorous mostly feeds
on decaying leaves. The general length is up to 75 cms.
Ø Body
is elongated hemispherical and slightly tapered at the posterior end.
Ø The
entire body is covered by exoskeleton
Ø Body
is divisible into cephalothoraxes and abdomen
Ø Both
the body parts bears paired appendages
Appendages:
Ø Appendages
are paired and biramous
Ø Basic
parts of appendages are protopodite, exopodite and endopodite. They are
modified according to their functions
Ø Total
appendages 19 pairs, of which 5 cephalic, 8 thoracic, 6 abdominal.
Ø Cephalic
appendages are: First antenna, Second antenna, Mandibles, First maxilla or
maxillula, and Second maxilla.
Ø Thoracic
appendages are: first Maxilliped, Second Maxilliped, Third Maxilliped , Walking
legs ( 5 pairs)
Ø Abdominal
appendages includes Pleopods or swimmerets and Uropod.
Cephalic
appendages
Maxillipeds
Walking
legs
Abdominal
Appendages
Digestive system
·
Process
of conversion of macro food molecules
into micro molecules by mechanical and enzymatic action is known as digestion.
·
The
digestive system of the prawn is divisible into Alimentary canal and Digestive
glands.
·
Alimentary
canal is divisible into three parts fore gut, mid gut and hind gut.
·
Fore
gut is lined by thick cuticle – the
parts are mouth, buccal cavity,
oesophagus, stomach,
·
Longest part of the foregut is stomach it is
divisible into cardiac and pyloric portions.
·
Mid
gut has internal epithelial lining.
·
Hind
gut has thick cuticle lining; it is divided into rectum and anus.
·
Digestive
gland includes hepatopancreas.
·
Prawn Digestive System
RESPIRATORY SYSTEM OF PRAWN
Respiratory organs
·
Respiratory system is modified for the aquatic
medium.
·
Respiratory
organs are :
·
1.
Branchiostegite
·
2.
Epipodites
·
3.
Gills
·
The
covering of the gill chamber is branchiostegite, which is the lateral extension
of the carapace.
·
Branchiostgite
is highly vascularised, hence supports the exchange of gaeses.
·
Epipodites
are small highly vascularisedleaf like membranous structures, present on the
maxillipeds. Present at the anterior part of the gill chamber.
·
Gills
are the primary respiratory organs.
·
Gills
are crescent shaped structures.
·
Basing
on the position gills are of three types, i.e., podobranch, Arthrobranch, Pleurobranch.
·
The
first gill is podobranch, second and eighth gills are arthrobranch and the
remaining gills are pleurobranch.
Course
of Blood circulation for gaseous exchange during respiration:
·
During the process of respiration vascularised
surfaces of the branchiostegites, gills and epipodites are bathed and gaseous
exchange occurs.
Prawn circulatory system
Circulatory system of prawn
·
Circulatory
system is open type, blood flows through body spaces, these spaces are referred
as haemocoels.
·
Parts
of the circulatory system are : Bllod, heart, Blood vessels and haemocoelomic
spaces.
·
Blood contains amoeboid leucocytes.
·
Blood
plasma contains copper containing respiratory pigment- haemocyanin, this
pigment is responsible for the blue colour of the blood.
·
Heart
is a triangular organ with spongy cavity,
·
Heart
is united with the pyloric stomach by a cardio pyloric strand.
·
Heart
is enclosed within the haemocoelomic space, i.e., pericardial sinus.
·
Wall of the heart is having five pairs of slit
like openings called ostia.
·
Ostia
are contractile, work as valves to permit the flow of blood from the
pericardial sinus to heart only.
·
True
blood vessels are called as arteries.
They arise from the heart. There
are six large blood vessels in prawn.
They are ophthalmic artery, a
pair of antennary arteries, a pair of hepato pancreatic arteries and a mid posterior artery these arteries gives rise to number of
branches which ends in blood sinuses.
·
Haemocoelomic
spaces : are the small spaces larger spaces , into
which the lacunae opens through haemocoelomic channels
Blood flow pattern
Prawn Excretory system
Excretory organs of Prawn
·
Green
glands or Antennal glands are the excretory organs
·
Excretory
organs are paired white organs, which located within the coxa of each second
antenna.
·
Parts
of the excretory organ are, End sac, Labyrinth, Bladder, Excretory opening.
·
Functions
:
·
1. Elimination of nitrogenous waste
products.
·
2.
Maintains of
osmotic equilibrium.
·
Ultra
filtration of the blood takes place during the process of excretion.
·
Along
with the green glands gills and
integument also participate in the process of excretion.
Prawn Nervous system
·
Nervous
system is advanced than the annelids, with sensory structures.
·
Divisible
into 1. Central Nervous System 2.
Peipheral Nervous System 3. Autonomic Nervous system.
·
CNS
runs from the anterior end to the posterior end of the body.
·
Brain,
circumoesophageal connectives , thoracic ganglionic mass, ventral nerve cord
are the parts of the Central nervous system.
·
Periperal
nervous system includes different nerves originating from the CNS, they are,
Optic nerve, Antennular nerve, Antennary nerve, Cephlothoracic nerves,
Abdominal nerves,
·
Autonomic
nervous system includes sense organs,
they are Tactile sense organs, Olfactory setae,
Statocyst and eye.
·
Compound eyes: Important sensory organ, it has number of
ommatidia or ocelli.
·
Each ommatidium has a outer dioptrical part
and an inner receptor region.
Sensory
organs of prawn
Prawn Reproductive
system
·
Exhibits
sexual dimorphism
·
Male reproductive system: Consists testes, Vas deference, Seminal vesicles, and male gonophores
Female reproductive system: consists of Ovaries, Oviducts and female
gonophores.
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