Download Mollusks - Bowie Aquatic Science

Phylum Mollusca
• Soft bodied
• Bilateral symmetry
• Head, foot, and coiled
visceral mass
• Most have external or
internal shell
• Brain
• Coelom: fluid filled cavity
• Over 100,000 species
Class Bivalvia (Bivalves)
• Two shells hinged
together by adductor
muscles
• Prey to sea stars,
predatory snails and
humans
Shell
• Lines on shells represent
age (like tree rings)
• Made of calcium
carbonate
• Produced by mantle-thin
membrane inside shell
• Mantle also makes pearls
by reacting to a grain of
sand.
Siphon Tube
• Protrudes through gap
btwn the clam’s shell
• Used for breathing and
feeding
• Two openings
• Incurrent siphon allows
water containing food and
O2 in
• Excurrent siphon allows
water containing wastes
and CO2 out
Respiration
• Gills- membranes that
take in O2 and give off
CO2
• Microscopic cilia beat
to create a current on
gills.
Feeding and Digestion
• Filter feeding: currents of
water that contain
plankton and organic
debris pass into the clam
through it’s incurrent
siphon, propelled by the
ciliary action of gill
surfaces. Cilia move the
food into the clam’s
mouth and into a one-way
digestive tract.
Circulation
• Open circulatory
system: nutrients and
O2 transported by a
colorless blood.
Movement
• Mussels: live in turbulent
intertidal zone w/ constant
wave action. Attach with
fibrous protein secreted by
foot
• Oysters: bottom shell
secretes a cement like
substance
• Use muscular foot to dig
in sand
• Contract and relax
abductor muscles
Reproduction
• Separate sexes
• External fertilization
• Young are part of
plankton community
Tridacna Clam
Class Gastropoda
• Snails, sea slugs
(nudibranchs),
limpets, abalone
• Gastropoda: one shell
“univalve”
• Operculum: thick pad
of tissue (protein or
calcium carbonate)
that closes like a trap
door over its foot.
Respiration
• Gills take up
oxygenated water
through the siphon
tube. Absorbs O2 and
releases CO2.
Feeding Styles
• Herbivores- (ex.
Periwinkle) graze on algae
with radula- ribbon-like
toothed structure.
• Scavenger-(mud snail)
feed on dead or dying
organisms. Use radula to
tear and shred the dead
matter into small pieces.
Feeding Styles
• Predator- actively hunt
and kill their food.
• Ex moon snail- feeds on
live clams by secreting
chemical to soften the
shell and then eat the
animal inside.
• Ex. Cone snail-uses toxins
from its harpoon-like
radula to kill its prey.
Cone Snail
Circulation
• Open circulatory
system w/ a one
chambered heart and
tiny blood vessels.
Movement
• Carried out by the
nervous and muscular
system working
together. Signals sent
from brain to motor
nerves.
Reproduction
• Many different methods
• Some have separate sexes;
some are hermaphrodites
• Fertilization is internal;
development is external.
• Many different methods:
Welk has egg casings;
moon snail has sand
collar; mud snail has
transparent jelly capsules.
Reproduction
• Egg casing of welk 
• Sand collar
Gastropod Diversity
• Abalone- produces mother
of pearl used for jewelry
• Slipper shell- live in
intertidal zone attached to
any hard substrate (even
horshoe crab); change
from male to female and
stack themselves up.
(Crepidula)
Gastropod Diversity
• Limpet- intertidal
zone of rocky coasts;
looks like a flattened
cone. (hole on top of
shell for wastes to
exit)
Gastropod Diversity
• Nudibranch (sea slug)lack or have a reduced
shell; breathe through skin
w/ tufts of gills on their
backs; eat hydroids and
anemones and use their
stinging as part of their
defense; very colorful to
serve as a warning. Sea
hare eat algae and some
turn green from all the
chlorophyll they consume.
California Sea Hare
• 75 cm in length=
largest gastropod in
ocean!!!!
• Releases a dye when
disturbed 
Class Cephalopoda
Cephalopods
• Examples: Squid, octopus, nautilus, and
cuttlefish
• means “head-foot”
• Prominent feature are head and tentacles
(modified foot)
• Swim by squirting jets of water through
their siphon
Feeding
• Capture prey with their muscular tentacles
with suction cups
• Parrot-like beak is used to kill and chew
food
• One way digestive tract
•
Reproduction
• Most cephalopods breed in shallow water
• Fertilization is internal and development is
external
• Male delivers packets of sperm to female
with its tentacle
Camouflage
• “Masters of Camouflage”
• Chromatophores: special pigmented cells
that can expand and contract causing
changes in skin pattern and coloration
• Ink:defense mechanism, used to distract and
confuse would be predators.
Nautilus
•
•
•
•
•
Chambered shell divided into compartments
New chamber is formed when it grows
Fill with gas
Slow moving
Preys on crabs, shrimp, and dead fish
Squid
• 10 tentacles, 2 longer than the rest
• Largest cephalopod is Architeuthis: giant
squid, up to 20 meters long
Octopus
• 8 tentacles
• Paralyzing venom is often injected into prey
along with bite
• Blue-ring octopus is so venomous it can
cause death in humans
• Brain and eye is highly developed
Cuttlefish
• Bottom dwelling
• Internal shell of calcium carbonate known
as a cuttlebone.
• 10 tentacles