Transcript MOLLUSCS

MOLLUSCS
1. Molluscs belong to the
phylum Mollusca.
There are more than 100,000
species known. They live
everywhere from the
deepest oceans trenches
to the tops of trees.
• 2. They can be as small as a
grain of sand or as large as
a school bus.
• 3. All molluscs have a
similar developmental
pattern. They develop from a
trochophore larva.
• 4. these larva float around in
the water and feed on
plankton. All mollusc
(except one) have an
internal or external shell.
• 5. Most mollusc have 4 main
body parts. These are the
foot, mantle, shell, and
visceral mass.
• 6. The muscular foot usually
contains the mouth and
feeding structures.
• 7. It may be adapted for
crawling or may be like
tentacles.
• 8. The mantle is a thin tissue
that covers most of the
body.
• 9. The shell is made by
glands in the mantle that
secrete calcium carbonate.
• Beneath the mantle is the
visceral mass. The visceral
mass contains the organs.
• 10. These basic body parts
have evolved to adapt to
different habitats. The type
of foot and kind of shell they
have are used to group
molluscs into classes.
• 11. Molluscs feed on about
everything. Most are
herbivores, carnivores or
filter feeders. A few feed on
detritus or are parasites.
• 12. Many molluscs like
snails and slugs feed by
using a structure called a
radula. A radula is a tonguelike structure consisting of a
layer of skin covered with
hundreds of tiny teeth.
• 13. It acts a feels like
sandpaper. It uses the
radula to scrape food
particles into its mouth.
• Carnivorous molluscs can
drill holes through the shells
of other animals using the
radula.
• 14. Once they create a hole
they will extend their mouth
and radula through it and rip
apart and swallow the soft
tissues of the animal.
• 15. Some carnivorous
molluscs like the octopus
and sea slugs have jaws
with a beak-like structure
they use to tear their prey
apart.
• 16. Some produce poison
used to kill their prey. Some
are fatal to humans.
• 17. Molluscs like clams,
oysters, and scallops are
filter feeders. They use
feathery gills to strain food
from the water.
• 18. They pass water over the
gills and tiny plankton gets
gets caught in the sticky
mucus covering the gills.
Cilia move the mixture of
mucus and food into the
mouth.
• 19. The gills are used in
respiration (to breath).
Terrestrial molluscs breath
by using specially adapted
mantle cavities that are lined
with blood vessels. This
must be kept moist in order
for gas exchange to occur.
• 20. The oxygen taken in
travels in the blood to
various parts of the mollusc.
The blood is pumped around
with a simple heart. Most
molluscs have an open
circulatory system.
• 21. This means the blood is
NOT contained within
vessels. The blood works its
way into open spaces in the
body called sinusus.
• 22. Squid and octopus have
a closed circulatory system
where the blood stays inside
blood vessels all the time.
This is a more efficient way
to circulate blood. Why do
you think they need a closed
system?
• 23. Undigested food is
removed in the form of
feces. Cellular waste has a
lot of ammonia in it.
Because ammonia is toxic it
has to be removed from the
body.
• 24. Molluscs get rid of
ammonia by using simple
tube-shaped organs called
nephridia which remove it
from the blood and release it
to the outside.
• 25. There is a wide variety of
nervous systems found in
molluscs. The simplest may
include a ganglia, ocelli, and
statocysts.
• 26. The more active
molluscs like squid and
octopus have very highly
developed nervous systems.
They are capable of
remembering and learning.
• 27. Reproduction – most
molluscs have two separate
sexes and fertilization is
external. The eggs and
sperm are released into the
open ocean and find each
other by chance.
• 28. This results in a free
swimming larva.
• In molluscs with tentacles
fertilization is internal.
• Some snails are
hermaphroditic. They will
get together and fertilize the
other ones eggs.
• 29. Class Gastropoda
• The name means stomach
foot. They got the name
because of the broad
muscular foot attached to
the stomach.
• 30. Gastropods include
snails, land slugs, abalones,
sea butterflies, sea hares
and nudibranchs.
• abalone
• Sea butterfly
• Sea hare
• Nudibranch
• 31. Many gastropods have a
single shell for protection.
They are able to retreat
inside when threatened.
They may also have a rigid
part of the foot called an
operculum that closes like a
door and seals them inside.
• 32. Some gastropods have
no shell (slug). For defense
they only emerge at night
when predators are not
around. Sea hares have ink
producing glands. The can
squirt ink into the water
which confuses the predator
• 33. Sea butterflies are
capable of swimming very
fast in order to escape
predators.
• Nudibranchs have special
chemicals in their bodies
that taste bad or are
poisonous.
• 34. Nudibranchs may also
be brightly colored. This
serves as an indication that
they are dangerous and not
good to eat.
• 35. Members of class
Bivalvia include clams,
oysters, scallops, and
mussels. They have two
shells that are hinged
together in the back and are
held together with one or
two very strong muscles.
• 36. Bivalve larva are free
swimming but as they grow
the become bottom
dwellers. Some live in the
sand or mud, other attach
themselves to rocks.
• 37. Some are sessile
(oysters) while others can
swim around (scallops).
• The shells are secreted by
glands in the mantle. These
glands also keep the inside
of the shell smooth by
secreting a substance
known as mother-of-pearl.
• 39. If an object gets caught
inside the mantle gland will
cover it with the mother-ofpearl and it will develop into
a pearl.
• 40. Class Cephalopoda
(head-foot)
• Members include octopi,
squid, cuttlefish, and
nautiluses. They range in
size from a 2 cm cuttlefish to
the colossal squids larger
than a school bus.
• 41. Most have eight flexible
tentacles each with round
sucking disks that are used
to grab and hold onto their
prey.
• 42. Cuttlefish and squid also
have two long slender arms
with suckers on the end
called feeding tentacles.
• 43. Nautiluses may have up
to 90 tentacles. These do not
have suckers but are
covered with sticky mucus.
• 44. The only living
cephalopod with an external
shell is the nautilus.
• Cuttlefish have a small shell
found inside the body called
a cuttlebone. (find one in the
pet store).
• 45. The squids internal shell
has been reduced over time
into a thin, flexible
supporting rod called a pen.
• Octopus have lost the shell
completely.
• 47. For protection most
cephalopods are capable of
swimming very quickly. They
may also use jet propulsion
by squirting water out of the
siphon which they are able
to direct in any direction.
• 49. Many cephalopods are
capable of changing color
rapidly by using
chromatophores in the skin.
• They are also capable of
producing an ink that clouds
the water allowing them time
to escape.
• 50. They also use
bioluminescence to attract
mates and scare off
predators.