Phylum Molluska
•Over 50,000 species
•Coelomate, Protostomes, Bilaterally
symmetrical
•Mostly marine, although some live in
fresh water or land.
•Generally soft-bodied with a hard shell
•However, squid & octopi have
internalized, reduced or lost their
shells.
•Body Plan
•Although phenotypically diverse,
mollusks share 3 common features
•A muscular foot - usually for movement
•A visceral mass - including internal
organs
•A mantle - envelopes visceral mass and
secretes a shell
Molusk General Anatomy
Class Polyplacophora
(chitons)
• Marine animals - shells divided into 8 plates
• Move using a muscular foot and graze using a
scraping mouthpart called a radula
Chiton Anatomy
Chitons
Class Bivalvia
• Include clams, oysters
and mussels
• Have shells divided
into 2 halves,
connected by strong
muscles
• Has hatchet shaped
foot for digging and
anchoring
• Are typically filter
feeders drawing in
water end expelling it
through a siphon tube
• Generally sessile,
however, some species
can quickly move by
rapidly closing it's
shell
Bivalve Anatomy
Bivalves
Class Gastropoda
• Include snails,
abalone, and slugs
• Largest class of
mollusks ~40,000
species
• Exhibit embryonic
process of torsion
• Visceral mass twists
1800 during development
• Most species are
herbivores, but some
have modified radullas
for boring into other
mollusks
• Some species have
successfully colonized
land
Gastropods
Giant African Land Snail
Class Cephalopoda
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Unlike other mollusks,
these are quick predators
Have beak-like jaws and
poison to catch &
immobilize prey
Beak is located @ the
center of several long
tentacles
Foot has been modified to
form a siphon which
allows most species to
move quickly using a jet
of water.
Only mollusks with a
closed circulatory system
(blood is always
contained in vessels)
Very highly developed
nervous system
Can learn complex
behaviors
Octopi have learned to
open jars to retrieve
prey
May have rudimentary
communication
Cuttlefish and octopi may
communicate by skin
coloration
Cephalopod Anatomy
Octopus
Squid
Cuttlefish
Cambered Nautilus