Transcript Phylum Mollusca pwrpnt

Phylum Mollusca
What is a mollusk?
• PHYLUM MOLLUSCA
• Slugs, snails, and squids are all mollusk.
• There is a wide variety of animals in this phylum—
from the slug that moves very slow to the squid
who is jet-propelled.
• Most species live in the ocean, but some live in
freshwater and moist land habitats.
• Some mollusks, such as oysters, live most of their
lives attached to the ocean floor or a boat that
has sunk.
• Others, like the octopus, swim freely in the ocean.
Phylum Mollusca
• Some mollusks have shells, and others do not.
• All mollusks have bilateral symmetry, a coelom, a
digestive tract with 2 openings, a muscular foot,
and a mantle.
• This is a membrane that surrounds the internal
organs of the mollusk.
• In mollusks with a shell, the mantle secretes the
shell.
A. How Mollusks Obtain Food
• Most mollusks have a structure called a radula
that helps them obtain food.
• This structure is located within the mouth.
• It is a tongue-like organ with rows of teeth.
• It is used to drill, scrape, grate, or cut food.
A. How Mollusks Obtain Food
• Octopus and squid are predators that use their
radulas to tear up the food they capture with their
tentacles.
• Other mollusks are grazers and some are filter
feeders.
B. Reproduction in Mollusks
• Mollusks reproduce sexually.
• In most aquatic species, eggs and sperm are
released at the same time into the water, where
external fertilization occurs.
• Many mollusks that live on land are
hermaphrodites, with internal fertilization.
• Some marine mollusks have free-swimming larvae
that propel themselves by cilia.
C. Nervous Control in Mollusks
• Mollusks have simple nervous systems that
coordinate their movement and behavior.
• Some more advanced mollusks have a brain.
• Most mollusks have paired eyes that range from
simple cups that detect light to the complex eyes
of an octopus that have irises, pupils, and retinas
similar to the eyes of humans.
D. Circulation in Mollusks
• Mollusks have a well-developed circulatory system
that usually includes a 2 or 3 chambered heart.
• In most mollusks, the heart pumps blood through
an open circulatory system.
• In this type system, the blood moves through
vessels and into open spaces around the body
organs.
• This adaptation exposes body organs directly to
blood that contains nutrients and oxygen, and it
also helps remove wastes from cell activites.
D. Circulation in Mollusks
• Some mollusks, such as octopi, move nutrients and
wastes through a closed circulatory system.
• In this system, blood moves through the body
enclosed entirely in a series of blood vessels.
• This system provides an efficient means of gas
exchange within the body.
E. Respiration in Mollusks
• Most mollusks have respiratory structures called
gills.
• These are specialized parts of the mantle that have
a rich supply of blood for the transport of gases.
• Gills increase the surface area through which gases
pass.
F. Excretion in Mollusks
• Mollusks are the oldest known animals to have
structures called nephridia.
• These are organs that remove waste from an
animal’s body.
• Mollusks have one or two nephridia that collect
waste from the coelom, which is located around
the heart only.
• Wastes are discharged into the mantle cavity, and
expelled from the body by the pumping of the gills.
Diversity of Mollusks
• Most of the common and well-known species of
mollusk are in 3 classes:
– Class Gastropoda
– Class Bivalvia
– Class Cephalopoda
A. Gastropoda
• This is the largest class of mollusks.
• They are also called the stomach-footed mollusks.
• This name comes from the way the animal’s large
foot is positioned under the rest of its body.
Gastropoda
• Most members of this class have a shell but some
do not.
• Some of the animals that do have a shell are
abalones, conchs, periwinkles, whelks, limpets,
cowries, and cones.
• These may be plant eaters, predators, or parasites.
Gastropoda
• A slug is one example of a gastropod that does not
have a shell.
• It is protected by a thick layer of mucus.
Gastropoda
• Colorful sea slugs, called nudibranches, are
protected in a different way.
• When sea slugs eat jellyfish, they take in the
poisonous nematocysts into their own tissues.
• Any fish that tries to eat the sea slug will get stung
by these nematocysts.
B. Bivalvia
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These are mollusks with 2 shells.
Some examples are clams, oysters, and scallops.
Most bivalves are marine.
They have no distinct head or radula.
Most use their large, muscular foot for burrowing
in the mud or sand at the bottom of the ocean.
• A ligament, like a hinge, connects their two shells
(valves) and strong muscles allow the valves to open
and close over the body.
• One of the main differences between gastropods
and bivalves is that bivalves are filter feeders.
C. Cephalopoda
• This class is the head-footed mollusks.
• It includes octopus, squid, cuttlefish, and the
chambered nautilus.
• The only cephalopod with a shell is the chambered
nautilus.
Cehphalopoda
• In this class, the foot has evolved into tentacles
with suckers, hooks, or adhesive structures.
• They swim or walk over the ocean floor after their
prey, capturing it with their tentacles.
• Once tentacles have captured prey, it is brought to
the mouth and bitten with strong jaws.
• Then the food is torn and pulled into the mouth by
the radula.
Cephalopoda
Cephalopoda
• Like bivalves, cephalopods have siphons (pumps)
that expel water.
• They can expel water in any direction and move
quickly.
• Squids can get up to speed of 20 m/s using this
system of movement.
• Squids and octopi also can release a dark fluid to
cloud the water.
• This “ink” helps to confuse their predators so they
can make a quick escape.