Download Phylum Mollusca

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50,000 or more species of molluscs.
They share 3 major sets of characteristics:
Body enclosed by a blanket-like mantle that secretes
a shell made of calcium or some other stiff structure.
 A mantle cavity between the mantle and the internal
organs; the anus, reproductive, and excretory ducts
open into the mantle cavity.
 A ventral, muscular foot that is highly modified
among the various groups of molluscs.
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Three main parts of a Mollusca
Visceral mass – Location of Organs
Mantle tissue makes a calcium carbonate shell
(may be reduced)
Foot = muscular structure modified in some
way (how determines class)- used for
movement
Reduced coelom
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Free-living, multicellular animals
Invertebrates (lack a backbone)
Unsegmented
Have a true coelom – BODY ADVANCE
Bilateral symmetry
Have a true heart
Simple to complex nervous system
Open circulatory System – BODY ADVANCE
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Some mollusc habitats include:
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Marine (mostly)
Freshwater (a few)
Land (a few)
Mollusc niches (life-style):
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Most live on the ocean bottom and are mostly
sedentary
Some are free-swimming (the cephalopods)
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There are seven mollusc classes in total six major ones,
of which we will study 3 of them.
Those 3 classes are:
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Gastropoda (gastro=body cavity; poda=foot)
 Ex. Common garden snail, abalone, turban snail
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Bivalvia (bi=two; valvia=valves)
 Ex. Clam
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Cephalopoda (cephalo=dealing with head; poda=foot)
 Ex. Squid, octopus, etc.
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Gastropods- The
most common type
of molluscs….Snails
Bivalves- The body
is compressed into a
two valved
shell….Scallop
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Cephalopods – Most agile of the molluscs
complex nervous system and a reduction or
absence of a shell. Highly Cephalized
Most popular class of molluscs.
 Consists of snails and snail-like
creatures.
 Specific characteristics:
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 They have a dorsally located shell (often
coiled).
 They have a well-developed radula.
Visceral mass (organs) is located inside
the shell. Their visceral mass is rotated
180 degrees during development.
 They are herbivores or predatory
(carnivorous).
 Habitats include: ocean, lake, river
bottoms, coastal shores, and land.
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1.Class: Gastropoda
(gastro=stomach; pod=foot) or Univalvia
(one shell)
ex: snail, abalone, conch
Their bodies are covered by one shell,
except for the nudibranch.
Most are benthic herbivores, although
the dog whelk is carnivorous.
Precious Wentletrap
Special tongue (radula) with a ribbon of flexible teeth on its surface
works like a mini-chain saw. It is used to scrape surfaces for algae
or to cut into other shells.
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Pseudopod
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Nudibranch
Cuttle fish
Octopus
Conch
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Specific Characteristics:
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They have no head.
They have two shells held
together by powerful muscles.
They have a ventrally located foot
that sticks out between the two
valves.
Habitats include: marine and
freshwater.
They tend to burrow into soft
mud or sand or attach to rocks or
other shells.
Large gills are used for
respiration and filter feeding.
Food is trapped by mucus on
the gills and moved by cilia.
Water enters and exits through
siphons.
2. Class: Pelecypoda or Bivalvia
(two footed, also two shells)
ex: clams, oysters, scallops
They are benthic, planktivores who filter sea water through an
incurrent and excurrent pore. Some are sessile (oyster) others
swim by opening and closing both shells (scallop).
Class Bivalvia
Clams, Oysters, Mussels
Byssal Threads
On Mussels
Scallops
Oysters
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Contains the largest molluscs.
HIGHLY CEPHALIZED
Specific Characteristics:
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May lack a shell (like an octopus)
Shell may be reduced to a stiffening rod (like the squid
or nautilus) A Chitionous Pen
The foot is highly modified to form a group of
tentacles around the mouth.
They are found in deep and shallow waters along
many coasts.
Squids & Nautilus are free-swimming and move very
quickly. Octopuses are found among rocks or crawling
on the bottom of the ocean.
Complex brain, two lateral eyes, excellent eyesight.
We will dissect a squid. If you are allergic to
shellfish then speak up now!!!
Class Cephalopoda
- mouth has a sharp beak for eating worms, fish, etc.
- moves by jet-propulsion, mantle fills with water which can be
squirted out to propel them backwards
- chromatophores in the skin change colors when the animal is
alarmed and for camouflage
- ink gland is used as a “smoke screen” for a quick escape
- eyes have a cornea, lens and retina; excellent vision
In the octopus, reproduction is by
internal fertilization. During the 30
days until hatching, the female
carefully aerate, cleans and watches
the eggs - never leaving even to eat.
The female usually dies from
exhaustion and starvation soon
after they hatch.
Cuttlefish
Chambered Nautilus
The cuttlefish has an internal shell that is sold to pet stores as
a source of calcium for birds. – a cuttle bone
The cuttlefish are masters of
Color change
Cells in their skin called
chromatophores cells which
are controlled by muscles to
create different colors.
Cuttlefish
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The spiraled shell of the chambered
nautilus is lined with mother-of-pearl
and is perfectly proportioned
mathematically.
Gas and liquid exchange occurs through
the walls and allows the nautilus to
regulate buoyancy.
Oysters are at the center of the aquaculture
industry and are raised for culturing pearls.
If an irritant such as a grain of sand gets trapped under the
oyster’s mantle, it secretes a coating of a pearl-like material called
nacre. Selected oysters are carefully raised to produce pearls of
various sizes and colors.
Bioluminescence