Mollusca

2. MOLLUSCA

3. WHAT IS MOLLUSCA
Molluscs are a clade
of organisms that all have
soft bodies which typically
have a "head“ and a "foot“
region.Often their bodies
are covered by a hard
exoskeleton, as in the
shells of snails and clams
or the plates of chitons.

4. GENERAL CHARACTARISTICS
 Tissue-system grade
of body organisation.
 Tripoblastic,
ceolomate,
unsegmented (except
monoplacophora)
and bilaterally
symmetrical.

5.  Body divisible into
head, mantle, foot
and visceral mass.
 Shell, when present,
usually univalve or
bivalve, constituing
in exoskeleton,
internal in some.

6.  Ceolom reduced and represented mainly by
pericardial cavity, gonadial cavity and kidney.
 Digestive system complete with a digestive gland
or liver (hepatopancrease); a rasping organ, the
redula, usually present.

7.  Circulatory system
mainly of closed type,
but some emptying into
sinuses; heart with one
or two auricles and one
ventricle; blood with
amoebocytes and
haemocyanin.
 Respiration direct or by
gills or lungs or both.
 Excretion by paired
metanephridia(kidneys)

8.  Nervous system of
paired ganglia,
connectives and
nerves . Ganglia
usually forms a
circumenteric ring.
 Sense organs include
eyes, statocystsand
receptors for touch,
smell or taste.

9.  Diococcus or
monococcus; one or two
gonads with gonoducts,
opening into renal ducts
or to exterior.
 Fertilization external or
internal; development
direct or through free
larval forms.
 Terrestial or
acquatic(freshwater or
marine).

10. CLASSIFICATION

11. BIVALVIA
 Body enclosed with
bivalve shell and
laterally compressed.
 No head,tentacles,eyes,
jaws and redula.
Example:
 Scallop
 Whelk
 Fileclamp

12. MONOPLACOPHORA
 Body bilaterally
symmetrical, with a dome
shaped mentle.
 Internal segmentation.
Example:
 Neopilina

13. GASTROPODA
 Well developed head
with eyes and tentacles;
redula present.
 Foot large and flat.
Example:
 Pila(apple snail)
 Patella(limpet)
 Slugs

14. CEPHALOPODA
 Body elongated
dorsoventrally.
 Head distinct and large
with well developed
eyes; foot as tentacles
and siphon.
Example:
 Nautilus
 Octopus

15. SCAPHOPODA
 Body within a tubular
shell, open at both
end.
 No head, mouth with
tentacles,no eyes.
Example:
 Dentalium
 Cadulus

16. APLACOPHORA
 Body worm-like
with a mantle.
 No shell and foot.
Example:
 Neomania
 Cheatoderma

17. POLYPLACOPHORA
 Dorso-ventrslly flattend
body.
 Shell as 8 calcareous
dorsal plates.
Example:
 Chaetoplura
 Chiton

18. PEARL CULTURE
A pearl is a hard
object produced within the
soft tissue (specifically the
mantle) of a living shelled
mollusc. Just like the shell
of a clam, a pearl is made
up of calcium carbonate in
minute crystalline form,
which has been deposited
in concentric layers

19. DEVELOPMENT OF A PEARL
A pearl is formed when the mantle tissue is
injured by a parasite, an attack of a fish or another
event that damages the external fragile rim of the shell
of a mollusk shell bivalve or gastropod. In response,
the mantle tissue of the mollusk secretes nacre into the
pearl sac, a cyst that forms during the healing process.

20. Chemically speaking,
this is calcium carbonate
and a fibrous protein called
conchiolin. As the nacre
builds up in layers of
minute aragonite tablets, it
fills the growing pearl sac
and eventually forms a
pearl. It is a myth that a
grain of sand or grit can
cause a pearl to form, as
nacre does not adhere to
inorganic substances.