Transcript Gastropods and Pelecypods - GMCbiology

Gastropods and
Pelecypods
How to make a living inside
your shell
Phylum Mollusca
Ancient Group of Animals
 Second “largest” animal phylum
 Over 100,000 extant species described
 Marine, freshwater, terrestrial (flying is
the only lifestyle mollusks haven’t
accomplished)
 Diversity of body forms
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Phylum Mollusca
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Class Gastropoda
Phylum Mollusca
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Class Gastropoda
Phylum Mollusca
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Class Gastropoda
Phylum Mollusca
Class Gastropoda
 Class Bilvalvia (Pelecypoda)
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Phylum Mollusca
Class Gastropoda
 Class Bilvalvia (Pelecypoda)
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Phylum Mollusca
Class Gastropoda
 Class Bilvalvia (Pelecypoda)
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Phylum Mollusca
Class Gastropoda
 Class Bivalvia
 Class Cephalopoda
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Phylum Mollusca
Class Gastropoda
 Class Bivalvia
 Class Cephalopoda
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Phylum Mollusca
Class Gastropoda
 Class Bivalvia
 Class Cephalopoda
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Phylum Mollusca
Class
 Class
 Class
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Gastropoda
Bivalvia
Cephalopoda
Polyplacophora
Phylum Mollusca
Class
 Class
 Class
 Class
 Class
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Gastropoda
Bivalvia
Cephalopoda
Polyplacophora
Monoplacophora
Phylum Mollusca
Class
 Class
 Class
 Class
 Class
 Class
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Gastropoda
Bivalvia
Cephalopoda
Polyplacophora
Monoplacophora
Scaphopoda
Phylum Mollusca
Class
 Class
 Class
 Class
 Class
 Class
 Class
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Gastropoda
Bivalvia
Cephalopoda
Polyplacophora
Monoplacophora
Scaphopoda
Aplacophora
What makes a mollusc a
mollusc?
The molluscan “bauplan”
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Body divided into three regions
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Head (typically reduced)
Foot
Visceral mass
What makes a mollusc a
mollusc?
The molluscan “bauplan”
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Body divided into three regions
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Head
Foot
Visceral mass
Body has a unique “organ” the mantle
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Covers the dorsal portion of the animal
Is folded into a “skirt” to form a chamber that houses the
gills, and openings for digestive, urinary, and reproductive
systems
May have several functions
Secretes a calcareous shell in some forms (bivalves, most
gastropods, some cephalopods, monoplacophora,
polyplacophra)
General Body Structure of a
Mollusk
What makes a mollusc a
mollusc?
The molluscan “bauplan”
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Body divided into three regions
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Head
Foot
Visceral mass
Body has a unique “organ” the mantle
 Nervous system consists of a pharygeal ring and a
two nerve chords
 “Closed” circulatory system
 Coelom is reduced (three sections, one surrounds the
heart, one the nephridia and the other the gonads)
 Bilateral symmetry (may be “lost” in adult forms)
 Use cilia for movement (locomotion or to move
water)
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What makes a mollusc a
mollusc?
The molluscan “bauplan”

Body divided into three regions



Head
Foot
Visceral mass
Body has a unique “organ” the mantle
 Nervous system consists of a pharygeal ring and a
two nerve chords
 Open circulatory system
 Coelom is reduced (three sections, one surrounds the
heart, one the nephridia and the other the gonads)
 Bilateral symmetry (may be “lost” in adult forms)
 Use cilia for movement (locomotion or to move
water)

What makes a mollusc a
mollusc?
The molluscan “bauplan”

Body divided into three regions



Head
Foot
Visceral mass
Body has a unique “organ” the mantle
 Nervous system consists of a pharygeal ring and a
two nerve chords
 “Closed” circulatory system
 Coelom is reduced (three sections, one surrounds the
heart, one the nephridia and the other the gonads)
 Bilateral symmetry (may be “lost” in adult forms)
 Use cilia for movement (locomotion or to move
water)

What makes a mollusc a
mollusc?
The molluscan “bauplan”

Body divided into three regions



Head
Foot
Visceral mass
Body has a unique “organ” the mantle
 Nervous system consists of a pharygeal ring and a
two nerve chords
 “Closed” circulatory system
 Coelom is reduced (three sections, one surrounds the
heart, one the nephridia and the other the gonads)
 Bilateral symmetry (may be “lost” in adult forms)
 Use cilia for movement (locomotion or to move
water)

What makes a mollusc a
mollusc?
The molluscan “bauplan”

Body divided into three regions



Head
Foot
Visceral mass
Body has a unique “organ” the mantle
 Nervous system consists of a pharygeal ring and a
two nerve chords
 “Closed” circulatory system
 Coelom is reduced (three sections, one surrounds the
heart, one the nephridia and the other the gonads)
 Bilateral symmetry (may be “lost” in adult forms)
 Use cilia for movement (locomotion or to move
water)
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Gastropods – Introduction
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Snails, slugs and others
The largest group of molluscs (over 40,000
recent species described)
Large foot used for locomotion (usually)
Posses a “radula” (used to scrape food in
grazing snails, highly specialized in some
groups)
Shell is coiled – result of “torsion” during
larval development
Gastropods – Introduction
Only mollusk group
to have terrestrial
forms
 Many species have
well developed eyes
 Head often has
tactile sensory
appendages
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Gastropods – Introduction
Only mollusk group to have terrestrial
forms
 Many species have well developed eyes
 Gas exchange via gills (most species) or
highly vascularized mantle cavity or
“lung” (pulmonate snails & some
terrestrial operculate snails)
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Gastropods – general form
Gastropods - Torsion
Gastropods – The radula
Scraping tool used
to feed
 Common to all
mollusks (except
bivalves)
 May be modified
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Cone snails – ocean predators
•In cone snails, the radula has been modified into “darts.”
•When the snail senses prey (such as the hapless fish, above)
the proboscis shoots out and one poison filled dart harpoons
the prey.
•The poison is a neurotoxin, that immobilizes the prey
•Cone snail venom may be fatal to humans
Gastropod Video
Part 1 http://www.youtube.com/watch?v=z6Z
2XCdmEwU
 Part 2 –
http://www.youtube.com/watch?v=O0lLQ
LAvYFI&feature=related
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Bivalves - Introduction
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Clams
Over 15,000 recent
species
Mostly marine
Common inhabitant
of deep sea thermal
vents
Freshwater forms
Bivalves - Introduction
Only mollusks to lack a
radula
 Classified based on gill
structure
 Reduced head
 Laterally compressed
 Hatchet-shaped foot
 Adapted for burrowing
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Bivalves – Life History
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First larval stage is a
trochophore (common
to all mollusks)
Morphs into veliger
stage
Veliger morphs into
juvenile (has same form
as adult)
Juvenile grows by
accretion at mantle
margin
Bivalves - Anatomy
Time to look at you
“clam”
 Northern quahog
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Venus mercenaria
Bivalves - External
Two valves
 Valves hinged on
dorsal side
 Notice the growth
lines (concentric
rings)
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Bivalves – Shell Morphology &
Physiology
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Most mollusks secrete a shell
Shell is composed of calcium carbonate (same
material used by corals)
Protected by periostracum
Prismatic layer (crystals oriented vertically)
Nacreous layer (crystals oriented horizontally)
Bivalves – Internal Anatomy &
Physiology
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Teeth – keep shells from
slipping
Ligament – connective
tissue that contracts when
shell is opened
Adductor muscles –
contract to allow the
animal to “clam up”
Pallial line – attachment
point for the mantle to the
shell
Pallial sinus – shows
position of the siphons
Bivalves – Internal Anatomy &
Physiology
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Mantle – surrounds the
body & apressed to the
shell
Contains sensory
organs (tactile tentacle,
light sensing eye spots
Secretes the shell
Is fused (two halves
joined) dorsally, open
ventrally
May be modified to
form siphons
Bivalves – Anatomy &
Physiology (Under the mantle)
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Foot
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Primary form of
locomotion
Animal pushes foot
into substrate
Foot is filled with
blood, causing it to
expand and grip
substrate
Clam pulls body
toward foot
Bivalves – Anatomy &
Physiology (Under the mantle)
Gills (ctenidia)
 Respiratory function
 Secondary function
is to filter water to
capture food
 Gill structure is used
to classify bivalves
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Bivalve gill evolution
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Protobranchs
(primitive)
Bivalve gill evolution
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Protobranchs (primitive)
Filibranchs
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Gills fold back to form a “U”shaped structure.
Mantle cavity divided by gills
into a ventral inhalent
chamber and a dorsal
exhalent chamber.
Chambers connect to outside
via siphons
Gills filter food from the
water passing across them.
Cilia move water across the
gills.
Bivalve gill evolution
Protobranchs
(primitive)
 Filibranchs
 Eulamellibranchs
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Bivalve gill evolution
Protobranchs
(primitive)
 Filibranchs
 Eulamellibranchs
 Septibranchia
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Bivalves – Anatomy &
Physiology (Under the mantle)
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Digestive System
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Labial palps surround
oral opening
Short esophagus
Stomach
Crystalline style
Bivalves – Anatomy &
Physiology (Under the mantle)
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The style – found in
many mollusks
Serves several functions
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“windlass” to pull food
string from esophagus
to stomach
Stirring rod
Source of digestive
enzymes
Bivalves – Anatomy &
Physiology (Under the mantle)
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Digestive System
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Labial palps surround
oral opening
Short esophagus
Stomach
Crystalline style
Intestine (loops
around stomach)
Rectum
Bivalves – Anatomy &
Physiology (Under the mantle)
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Circulatory System
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Pericardium encloses the
heart
Heart has two auricles and
one ventricle
Circulatory system is open
(blood passes from arteries
into sinuses in the tissue and
then back into veins).
Most clams have
haemocyanin as the blood
pigment. Some have
haemoglobin.
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Bivalves – Anatomy &
Physiology (Under the mantle)
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Urogenital System
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Posses two nephridia
(similar to kidneys)
Most bivalves are
dioecious
Gonads are usually
adjacent to the intestine
Gonads and nephridia
discharge to the
posterior portion of the
mantle cavity
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