Download Phylum Mollusca

Phylum
Mollusca
Largest Classes
Class Gastropoda - snails
Class Bivalvia - clams, mussels,
oysters, scallops.
Class Cephalopoda - squid,
nautilus, octopus.
General Characteristics
i. Second largest phylum of animals and
second most successful land animals,
next to insects. There are more
terrestrial mollusks than terrestrial
vertebrates.
ii. Includes snails,
clams, octopus.
Blueringed
Octopus
Caribbean
Octopus
Squid
Scallop
Mollusks have 3 body regions:
a head/mantle, a visceral mass, and a
"foot."
Nudibranch
Mollusks have well developed
body organs (nervous system,
circulatory system, respiratory
system, etc.) but lack body
segmentation.
iii.
Body cavity (coelom) is
completely surrounded by mesoderm.
iv.
Coelom allows space for more
complex internal organs.
* Digestive tract can be longer than the
animal.
* Allows larger reproductive system.
Nutrition
The longer digestive tract allows better digestion
Circulation
A large body cavity requires the
development of an efficient circulatory
system.
A network of vessels carries fluid (blood)
to all parts of the body. Blood carries
nutrients and oxygen to cells and
carries wastes and carbon dioxide
away. Circulation is accomplished by
the contraction of a muscular heart (or
hearts).