Download Mollusca

Phylum
Mollusca
Phylum Mollusca
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Mollusks are soft-bodied animals that usually
have an internal or external shell.
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Mollusks include:
- Snails
- Slugs
- Clams
- Squids
- Octopus
Mollusca Characteristics
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Soft body
External or internal shellMuscular foot and visceral mass (covered by
mantle)
Radula in some-used to scrape food
Bilateral symmetry
No segments
Coelomates
Open circulatory system- blood not always in
a vessel
Trochophore larvae
Trochophore larvapaddlelike, bristles
Apical tuft
Stomach
Ciliary band
Mouth
Anus
4
Phylum Mollusca: Anatomy
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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
The muscular foot takes many
forms:
flat structures-crawling
4.
spade-shaped- burrowing
tentacles-capturing prey.
clip-giant octopus capturing preyl
Phylum Mollusca: Feeding
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Some Mollusks have a radula: a rough, tonguelike organ with rows of teeth-like structures.
-scrape algae off surfaces
- rasp up flesh from prey.
Body Systems
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Muscular-Skeletal - outer shell, soft body, muscular
foot for movement.
Digestion food brought in through a siphon
system mouthdigestive gland intestineanus.
Nervous- A Mollusk has no formal nervous system,
but has a series of ganglia that conduct impulses.
Circulatory - heart, blood and blood vessels, open
Respiratory- tubes called siphons- bring water in and
out of their bodies to take in oxygen and give off
carbon dioxide.
gills- help with this.
Reproductive- separate males and females and
reproduces sexually with a large gonad.
Excretion- nephridium that gets rid of wastes anus
Classes of Mollusks
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There are 8 classes of Mollusks (Covering 5)
 Class
Monoplacophora: placo=-plate; mono
= one
 Class Polyplacophora: Chiton
 Class
Gastropoda: snails, slugs, & sea hares
 Class
Bivalvia: clams, oysters, mussles &
scallops
 Class
Cephalopoda: octopus, squids, cuttlefish,
& nautilus
Class Monoplacophora
Mono= one
 Placo=plate
 Phora= to have or bear
 Mollusks with a single, curved shell
 Marine
 Thought to be extinct until one was found
in 1952
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Class Polyplacophora
Poly = many placo= plates
 shell is divided into 8 curved plates
or shells
 Marine
 Have a reduced head and a flattened foot
 Ex. Chiton
Polyplacophora
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When disturbed, the edges of the mantle
tightly grip the substrate creating a powerful
vacuum that holds the chiton in place
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Has the ability to roll into a ball when dislodged
Quick Check:
Compare and contrast Class
Monoplacophora with Class Polyplacophora.
(How are they similar? How are they
different?)
Class Bivalvia
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Clams, Oysters, Mussels & Scallops
Live in water, filter feeding
 2 shells held together by powerful
muscles(hinges)
 No radula
 Hatchet shaped foot for
burrowing
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Class Bivalvia
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only Mollusks that do NOT have a radula
Feed by siphoning and filtering large particles
from water
 Can survive for short times out of water by
closing their valves
 Scallops can move around by flapping their
shells when threatened.
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Class Bivalvia
Oyster Catcher
Willet
Plover
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Starfish, many sea birds (Oyster Catchers, willets,
plovers, and much more), and walrus feed on them
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The largest bivalve is the Giant clam (clip)
Can weigh more than 450 lbs
Class Bivalvia: Making Pearls
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Oysters filter-feed
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An irritant, such as a grain of sand, becomes
embedded in the mantle.
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The animal coats the irritant with the same material
used to produce the lining of its shell called motherof-pearl.
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The coating makes the irritant less painful.
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It continues to coat the irritant, creating a pearl.
Class Bivalvia
Importance
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Bivalves are filter feeders
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valuable service by reducing suspended particles in
their habitats
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If their populations are reduced, the water in that area
will become turbid (cloudy)
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Turbid water reduces light penetration for
photosynthesis in sea-grasses and algae
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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
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GOOD!
Class Gastropoda
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Gastropoda means “stomach foot”
Includes snails, slugs, & sea hares
Most are single shelled- asymmetrical and
coiled
 Some are shell-less (slugs & sea hares)
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Radula for scraping food
Class Gastropoda
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They are 2nd only to insects in their number of
known species
They can live in gardens, woodland, deserts,
rivers and lakes; estuaries, mudflats, the rocky
intertidal, the sandy subtidal, in the depths of
the oceans, and many other ecosystems
queen-conch/strombus-gigas/video-00.html
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Class Gastropoda
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They move using a muscular foot
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Many have 2 or 4 tentacles
with eyes on the tip
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Most have a coiled shell that
opens to the right
The Lightning Whelk is the only
“left handed” snail
Gastropod clip- Oahu tree snail
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Class Gastropoda
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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
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Many animals feed on gastropods
-- Example: Sea otters eat abalone
Class Gastropoda
Hermit crabs inhabit empty snail shells.
 When the crab gets too big for the shell, they
find a larger one.
 Hermit crabs have wars for prized shells.
http://www.arkive.org/common-hermitcrab/pagurus-bernhardus/video-03.html
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Class Gastropoda
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Suborder Nudibranchia
- Means “Naked gill”
- marine, shell-less gastropods
- The gills are arranged as feathery
plumes on their backs
- Are brightly colored
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Warning: many are poisonous
Camouflage
Quick Check:
Why are gastropods important? What would
happen if all gastropods went extinct?
Class
Cephalopoda
Class Cephalopoda
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Typically soft-bodied with the head attached to
a single foot.
The foot is divided into tentacles or arms.
Cephalopoda Locomotion
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Most swim by forcefully expelling water from
the mantle cavity through a ventral
funnel (Siphon).
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Swim using jet propulsion method.
Funnel can point forward or backward to
control direction
The force of water expulsion determines speed.
Cephalopoda Feeding
 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
Chromatophores: 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:
- Camouflage
- Communication (alarm/courtship)
- Many are bioluminescent to attract prey
and mating partners!
Octopus are Highly Intelligent
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Maze and problem-solving experiments have
shown that they do have both short- and longterm memory.
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Can be trained to distinguish between different
shapes & patterns
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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:
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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!
http://www.gadling.com/2011/09/27/video-eating-liveoctopus-in-korea-warning-graphic/
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:
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Most of the shell has disappeared, leaving only
a thin, horny strip called a pen which is
enclosed in the mantle.
Cephalopoda
Squid:
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Giant Squid are the largest
invertebrate
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Have the largest eyes in
the animal kingdom
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Never been seen alive!!!
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Their bodies wash up onto
beaches
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Sperm whales feed on giant squid
Giant Squid
Forms of Cephalopoda
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Nautilus
Forms of Cephalopoda
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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
Quick Check
How are squid different than octopus?
Table 1 Classes of the Phylum Mollusk
Scientific Name
Pronunc Common
iation
Name
Polyplacophore
chitons
Monoplacophores
Gastropoda
GAStrohpahdz
Bivalvia [Pelecapoda]
Cephalopoda
SEHFuh-lohpahdz
# Shells Foot
# of
Species
8-plates
~650
1
? extinct
univalves
(snails,
slugs)
1 or
none
stomach
foot
bivalves
2
hatchet foot ~8000
octopus,
squids
internal
head foot
~90,000
~650
Polyplacophore (many plates). [Amphineura].
The End of Mollusca