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Mollusca is the second largest phylum
in the animal kingdom. In Latin
Mollis means soft. The animals of
this phylum have a soft body. Hence
they are called molluscans.
Aplacophora (including
Caudofoveata and Solenogastres)
Monoplacophera
Polyplacophora
Scaphopoda
Gastropoda
Bivalvia
Cephalopoda
 The animals are mostly aquatic &
some are found in moist soil.
 They are triploblastic animals. The
body of these animals are
unsegmented. The body has three
divisions namely head, ventral
muscular foot, mantle.
 The inner body wall is thick &
covered by muscles. A part of this
is modified for locomotion.
 Digestive system is complete with mouth,
oesophagus,& anus. Mouth has a muscular
organ called RADULA, bearing row of teeth,
which help in grasping food. The radula serves
both to scrape off algae and other food
materials and also to convey them backward
to the digestive tract..
 Mollusca has an excretory system with an
anus. It has an organ called the nephridium
that gets rid of wastes.
Respiratory system
 Respiration takes place through
special structure called Ctenidia found
in the mantle cavity & through
epidermis of the mantle cavity itself
which are typically flattened, lamellar
structures with a central axis from
which numerous smaller gill filaments
project.
 A Mollusca has tubes called siphons
that bring water in and out of their
bodies so that they can get oxygen and
give off carbon dioxide. They have
gills that help with this.
CIRCULATORY SYSTEM
 The blood vascular system contains the
heart & the associated blood vessels. The
heart has auricles & ventricles.
 A Mollusca has a heart, blood and blood
vessels.
 Blood may be colorless fluid or bluish
green in color or red in color containing
HAEMOGLOBIN.
NERVOUS SYSTEM
 A Mollusca has no formal nervous
system, but has a series of ganglia
that conduct impulses.
 Different types of sense organs like
eyes, tentacles, balancing organs & to
perceive smell, organs of equilibrium,
are present.
 A pair of nephridia serve as an
excretory organ, open on the body
through the pores.
REPRODUCTION
1.In the molluscs reproduction is
sexual.
2.Sexes are separate.
3.In some animals male & female
reproductive organs are found in
the same individual
4.A Mollusca is either male or female
and reproduces sexually with a
large organ called a gonad.
CHITON
OCTOPUS
SNAIL
NEOPOLINA
TWO SHELLS
SCALOP
SHELLS
BIVALVIA
A SHELL
CLAM
A CLAM
The GIANT SQUID is the largest among
invertebrates. It is about 2000k.gms. in
weight.
 Lamellidens lives in sand. Its shells are
composed of right & left halves.
Octopus is also known as devil fish
which lives in bottom in the shallow
water along the coast.
 Octopus is one of the largest
invertebrates It gets the name
because of the presence of 8
long arms in its head region.
 Octopus has an ink gland in their
body. To confuse the enemy they
squirt ink out of the siphon & can
not be seen behind the dark
watery screen.
 Beautiful shell are used in making
decorative materials.
 Pearly layer is used for making
buttons.
 Shells are used in preparing lime,
which serves as food for poultry
birds to improve their egg
production.
 Certain bivalves are used as food.
 Cowries are used for playing are
also the shells of mollusc. They
are beautiful & shining.
 The shell of cuttle fish is found
inside the body. It is rich in
calcium & is used for cleaning
glasses.
 Pearl oyster gives pearl which
is used as pearl.
FORMATION OF PEARL
OYSTER
PEARL OYSTER IS A MOLLUSCA WHICH IS
KNOWN FOR PRODUCING PEARLS OF
COMMERCIAL IMPORTANCE. THE FORMATION
OF A PEARL OCCURS WHEN AN UNWANTED
SUBSTANCE SUCH AS STONE OR A SAND
PARTICLE ENTERS THE BODY. THE PARTICLES
BECOME SURROUNDED BY A SECRETION
PRODUCED BY GLANDS IN THE SHELL. THE
SECRETION GRADUALLY HARDENS TO FORM A
PEARL. THIS NATURAL PROCESS HAS BEEN
USED BY MAN FOR ARTIFICIAL PRODUCTION
OF PEARLS.
PROJECT DONE BY,
K.S.SINDHU RAO
DEEPIKA R.R.