PHYLUM MOLLUSCA
WHAT IS A MOLLUSK?
Why are animals that look and
act so different grouped in the
same phylum? It is because
they share developmental
patterns.
Characteristics of Mollusk
1. mantle
2. mantle cavity
3. shell
4. true coelom
5. head, muscular foot, visceral
cavity
6. systems: circulatory, respiratory,
digestive, excretory,
reproductive, and nerve
impulses
Mollusks are well defined as
soft bodied animals that
either have an
external or internal shell.
Their name comes from the
Latin word molluscus
meaning soft.
Most mollusks are composed of 4 basic parts:
– foot - flat surface adapted for
locomotion and usually contains the
mouth and other feeding structures
– mantle - covers most of the body and
secretes the shell
– shell - composed of calcium carbonate
– visceral mass - contains the internal
organ
Unique features of most
mollusks include
• Mantle
• ctendia - special gill which are
also used for filter feeding
• radula - rasping tongue-like
structure used for scraping
INTERNAL TRANSPORT
OPEN CIRCULATORY SYSTEM
In open circulatory systems, the blood is not
always contained in vessels. There is a
simple heart and a few arteries but there are
no veins. Blood leaves the heart and
bathes the internal organs and travels
through the body in open spaces called
sinuses. These sinuses lead the blood to the
gills where oxygen and carbon dioxide are
exchanged (diffusion).
What is a closed circulatory system?
Excretion All animals must remove waste
products An open circulatory system
will work well for slow
moving animals. Why is an open
circulatory system not adequate for
fast-moving animal