Download Mollusk NOTES

Phylum Mollusca

Mollusks are soft-bodied animals that usually
have an internal or external shell.

Mollusks include:
- Snails
- Slugs
- Clams
- Squids
- Octopus
Phylum Mollusca: Anatomy

The body plan of most have 4 parts:
mantle, shell, visceral mass, and foot.
1.The mantle is a thin layer of tissue that covers
most of the mollusk’s body like a cloak.
Phylum Mollusca: Anatomy
2. The shell is made by glands in the mantle that
secretes calcium carbonate.
-- Reduced or lost in slugs
-- Internal or lost in Cephalopods
(squid/octopus)
Phylum Mollusca: Anatomy
3. Visceral mass is just beneath the mantle and
consists of the internal organs.
Phylum Mollusca: Anatomy
4.
The muscular foot takes many forms,
including flat structures for crawling, spadeshaped for burrowing, and tentacles for
capturing food.
Phylum Mollusca: Feeding

Mollusks are herbivores, carnivores, filter feeders,
detritivores, and parasites.
***Review!***

Detritivores are organisms that feeds on plant
and animal remains and other dead matter.

Herbivores are organisms that feeds on plants.

Carnivores feed on animals.
Phylum Mollusca: Feeding

Mollusks have a radula: a rough, tongue-like organ
with rows of teeth like structures. Some use it to
scrape algae off surfaces, and other use it to rasp up
flesh from prey.
Classes of Mollusks

There are 8 classes of Mollusks (Covering 4)
 Class
Polyplacophora: Chiton
 Class
Gastropoda: snails, slugs, & sea hares
 Class
Bivalvia: clams, oysters, mussles &
scallops
 Class
Cephalopoda: octopus, squids, cuttlefish,
& nautilus
Polyplacophora
Includes Chiton

Marine

Have a reduced head and a flattened foot

The shell is divided into 8 articulating
dorsal valves
Polyplacophora


When disturbed, the edges of the mantle tightly grip
the substrate creating a powerful vacuum that holds
the chiton in place
Has the ability to roll into a ball when dislodged
Class Gastropoda

Gastropoda means “stomach foot”

Includes snails, slugs, & sea hares

Most are single shelled

Some are shell-less (slugs & sea hares)
Class Gastropoda

They are 2nd only to insects in their number of
known species

Can be found living in gardens, in woodland, in
deserts, rivers and lakes; in estuaries, mudflats,
the rocky intertidal, the sandy subtidal, in the
depths of the oceans, and many other
ecosystems
Class Gastropoda

They move using a muscular foot

Many have 2 or 4 tentacles
with eyes on the tip

Most have a coiled shell that
opens to the right

The Lightning Whelk is the only
“left handed” snail
Class Gastropoda


Many have an operculum that is used as a
“trap-door” to close the body inside the shell
Most breath using gills
Class Gastropoda: Importance

Many animals feed on gastropods
-- Example: Sea otters eat abalone
Class Gastropoda




Hermit crabs inhabit empty snail shells.
The crabs do not make the shells, the snails do.
When the crab gets too big for the shell, they
find a larger one.
Hermit crabs have wars for prized shells.
Class Gastropoda

Suborder Nudibranchia
- Means “Naked gill”
- Are all shell-less gastropods
- The gills are arranged as feathery
plumes on their backs
- Are brightly colored


Warning: many are poisonous
Camouflage
Class Bivalvia
 Clams, Oysters, Mussels & Scallops


Have 2 shells that are held together by powerful muscles.
Scallops can move around by flapping their shells when
threatened.
Class Bivalvia

Live exclusively in water

The only Mollusks that don’t have a radula

Feed by siphoning and filtering large particles
from water

Can survive for short times out of water by
closing their valves
Class Bivalvia
Oyster Catcher
Willet
Plover
Oyster Catcher
 Starfish, many sea birds (Oyster Catchers, willets, plovers, and
much more), and walrus feed on them
•
The largest Gastopod is the Giant Clam
•
Can weight more than 450 lbs
Class Bivalvia: Making Pearls

Oysters filter-feed

An irritant, such as a grain of sand, becomes
embedded in the mantle.

The animal coats the irritant with the same material
used to produce the lining of its shell called motherof-pearl.

The coating makes the irritant less painful.

It continues to coat the irritant, creating a pearl.
Class Bivalvia

Bivalves are filter feeders

Because they filter feed, they provide a valuable
service by reducing suspended particles in their
habitats

If their populations are reduced, their water in that
area will become turbid (cloudy)

Turbid water reduces light penetration for
photosynthesis in sea-grasses and algae

Without plants, many other populations of organisms
will also decrease
Class Bivalvia: Eating Bivalves
Mmmmmmm…
Mmmmm….
“Oysters on a half-shell”
 Considered an aphrodisiac
 Eaten fried, Steamed, or raw

GOOD!
Class Cephalopoda


Typically soft-bodied with the head attached to
a single foot.
The foot is divided into tentacles or arms.
Cephalopoda Locomotion

Most swim by forcefully expelling water from
the mantle cavity through a ventral
funnel (Siphon).



Swim using jet propulsion method.
Funnel can point forward or backward to
control direction
The force of water expulsion determines speed.
Cephalopoda Feeding

Cephalopods (squids/octopus) have beaks:
similar to a bird’s beak, used for crushing and
picking apart food.
Beak
“Masters of disguise!”
-- Color changes are possible due to special
pigment cells contained within its skin, called
chromatophores.
Cephalopoda
These cells which are small structures filled
with colored ink which can be expanded
and contracted to communicate with
others or as camouflage against the
landscape.
Cephalopoda
Color changes are used for:
- Camoflague
- Communication (alarm/courtship)
- Many are bioluminescent to attract prey
and mating partners!
Octopus are Highly Intelligent

Maze and problem-solving experiments have
shown that they do have both short- and longterm memory.

Can be trained to distinguish between different
shapes & patterns

Observed having
observational skills
Class Cephalopoda
Octopus:
- Have
8 arms
- Arms have sucking disks
that grab & hold prey.
- Blood is pale blue.
- The shell is absent!
Class Cephalopoda
More
Octopus:
- When female lays eggs, she stops eating,
& protects her eggs until she dies.
Class Cephalopoda
Blue-ringed Octopus:
- The most toxic
- A bite is nearly always fatal to humans.
Giant Octopus:
-
Can weigh 600 lbs
Known to attack ROV and bite into metal
Class Cephalopoda
•
People eat octopus: Dead or ALIVE!
•
A dish called “San Nakti” means “living octopus”
-- Kind of difficult to get the octopus down because
the tentacles stick to your mouth and throat.
-- They also have a tendency to walk off your plate!
Hungry?
Hungry?
Cuttlefish & Squid
Have 10 appendages (decapods):
8 arms with suckers and 2
long retractile tentacles
Forms of Cephalopoda
Cuttlefish:
-- Have an internal gas filled “bone” that helps
with buoyancy called the cuttlebone.
-- Well, it is not for sharpening the beak. It's
amazing how many pet owners think this is its
purpose. Cuttlebone is provided to birds as a
source of calcium and other necessary
minerals. It is especially important to breeding
hens.
Forms of Cephalopoda
Squid:
-- Color changes reflect the animal’s mood.
-- Messages:
ready to mate, sexual identification, alarm,
ready to hunt, & hiding.
Cephalopoda: Squid
Squid:

Most of the shell has disappeared, leaving only
a thin, horny strip called a pen which is
enclosed in the mantle.
Cephalopoda
Squid:

Giant Squid are the largest
invertebrate

Have the largest eyes in
the animal kingdom

Never been seen alive!!!

Their bodies wash up onto
beaches

Sperm whales feed on giant squid
Forms of Cephalopoda

Nautilus
THIS
Nautilus!
Or THIS
Not THIS
Nautilus
Nautilus
Forms of Cephalopoda

Nautilus
-- Sticking out from the shell is the nautiluses’
arms and a leathery hood that closes the
animal into its shell for protection.
-- This nautilus has more than 90 arms.
Forms of Cephalopoda
More Nautilus:
-- The only cephalopod encased in a shell.
-- The nautilus can fill the chambers it doesn’t
occupy with gas or water. If the chambers are
filled with gas, the animal will float. If the
chambers are filled with water, the animal will
sink.
Forms of Cephalopoda
More Nautilus:
-- The living animal inhabits only the last
chamber.
-- As it grows, it moves forward, secreting
behind it a new septum.
-- The chambers are connected by a cord of
living tissue called a siphuncle, which
extends from the visceral mass.
Nautilus