Transcript Unit 6.1 - Mollusca - Jutzi

Unit 6.1
Phylum Mollusca
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Mollusks
• 50,000 -100,000 living
species
• 35,000 extinct species
• Largest = 1000 pounds
• 80% less than 5 cm
• Soft body
• Most have a shell
• Most marine
• Snails terrestrial
– Most habitat
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Phylum Mollusca
• Ventral Foot
– Locomotion
• Mantle
– Encloses body cavity
• Shell – created by
mantle
• Coelom (eucoelomate)
• Visceral mass contains
contains organs of
digestion, circulation,
excretion, &
reproduction
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Phylum Mollusca
• Radula – rows of
posteriorly oriented
teeth. Basically a
tongue with teeth
• Open circulatory
system
– Closed in cephalopods
• Mantle cavity – opens
to the outside and
functions in gas
exchange
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Economically Important
• Pearls
• Burrowing shipworms
• Snails & slugs
– Garden pests
– Food
– Intermediate hosts for
parasites
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Trochophore Larva
• Same type as Phylum
Annelida
• Shows phylogenetic
relationship to higher
taxa
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Uniramia
Echinodermata
Chelicerata
Vertebrata
Lophophores
Crustacea
Other Chordata
Arthropoda
Annelida
Hemichordata
Other
pseudocoelomates
Nematoda
Mesozoa
Sarcomastigophora
Ciliophora
Apicomplexa
Microspora
Mollusca
Nemertea
Platyhelminthes
Ctenophora
Cnidaria
Placozoa
Porifera
Myxozoa
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Generalized Mollusk
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Body Plan
Pericardial cavity
Metanephridium
Mantle cavity
Gonad
Ctenidium
Radula
Stomach and digestive gland
Foot
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Dorsal mantle covers the
visceral mass.
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Secretes the shell
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Ctenidium (Respiration)
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Complete digestive system
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Paired ventral nerve cords
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Radula
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Radular Structure
Source: From A Life of Invertebrates, Copyright © 1979 W. D. Russell-Hunter.
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Coelom - metanephridia
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Class Polyplacophora
Chitons
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Class Polyplacophora
• Eight dorsal plates
• Fishy flavor & tough
to chew
• Reduced head
• Radula reinforced
with iron
– Scrape algae from
rocks
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Class Polyplacophora
Mouth
Mantle cavity
Ctenidium
Foot
Anus
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Class Polyplacophora
Digestive
gland
Mouth
Stomach
Gonad
Pericardial cavity
Nephridium
Anus
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Class Bivalvia
Clams, Oysters, Mussels, & Scallops
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Class Bivalvia
• Two shells actually
form as a single
structure
• Most are filter feeders
– helpful in removing
bacteria from polluted
waters
• No head or radula
• Burrowing animals
– Sand, wood, rocks
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Giant Clam & Burrowing Clam
Muscular Foot
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Zebra Mussel
• Environmental Pest
• Ballast water of ships
from Europe in 1986
• Attach by secreting
adhesive byssal
threads
– Each other
– Other mussels
– Man made objects
• Pipes, plumbing
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Zebra Mussel
• Live in high densities
• Feed on
phytoplankton
• Reproduce rapidly
• Attach to native
mussels
• Killed all native
mussels in Lake Erie
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Distribution of Zebra Mussel
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Bivalve structures
Hinge
Labial palp
Ctenidium
Excurrent
siphon
Foot
Incurrent
siphon
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Clam anatomy
Pericardial cavity
Metanephridium
Heart
Intestine
Excurrent
Stomach
Incurrent
Intestine
Gonad
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Clam anatomy
Digestive
gland
Excurrent
Stomach
Incurrent
Intestine
Gonad
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Clam anatomy
Pericardial cavity
Heart
Intestine
Excurrent
Incurrent
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Clam anatomy
Metanephridium
Pericardial cavity
Heart
Intestine
Excurrent
Incurrent
Gonad
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Oysters
• Able to form pearls – the
color depends on prevalent
minerals in water
• Only eat oysters during
cold months – less bacteria
in filtrate
• Can cause severe wounds
and Vibrio infections
• Use extreme caution when
exiting boats in oyster
infested waters
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Vibrio vulnificus
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Pearl formation
Shell
Developing pearl
Epithelium
An irritant, usually sand, becomes lodged between the shell
and mantle. Layers of shell are then secreted by the mantle
around the foreign material. The mineral content of the
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water determines the color of the resulting pearl.
Scallops
• Good swimmers – the
only migratory bivalve
• Movement achieved
by rapidly opening
and closing shell
• Mostly free-living
• Highly regular and
geometrically
symmetrical shells
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Shipworms
• Highly reduced shells.
• Known as termites of
the sea.
• Burrow into any
submerged wooden
structure including
ships, docks, & piers.
• Special gland called
Deshayes gland
contains bacteria that
allow shipworms to
digest cellulose
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Shipworms
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Class Gastropoda
Snails, Slugs, Conchs, Abalones, & Limpets
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Class Gastropoda
• One shell (if present)
• Torsion of body –
allows head to retract
before tail, allows
clean water to enter
mantle cavity, and
orients sensory
organs in direction of
forward movement.
• Largest & most varied
molluscan class
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Torsion
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Snails
• Terrestrial is most
encountered type but
marine varieties are
much more numerous.
• Mantle cavity functions
as lung in terrestrial
snails.
• Herbivores, omnivores,
and carnivores.
• All land snails are
hermaphrodites.
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Snails
Shell
Pneumostome
Tentacle
(Eye stalks)
Tentacle
Anus
Foot
Mouth
Genital pore
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Internal Structure of a Generalized Gastropod
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Nudibranchs
• No shell – commonly
called sea slugs
• Dorsal projections aid
in respiration and
protection – they eat
hydroid cnidarians,
conserve the
nematocysts, and
move them to the
dorsal projections
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Nudibranchs
• Some of the most colorful
creatures on earth.
• Unlike most other
gastropods, they are
bilaterally symmetrical.
• One species of
nudibranch is the only
animal that can
photosynthesize.
However, it must also eat
to satisfy all of its energy
needs.
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Nudibranchs
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Abalones
• Several holes in top
of shell
– Excrete waste
– Used for respiration
• Shell is incredibly
strong. It is made of
microscopic calcium
carbonate tiles
stacked like bricks.
• Live primarily on
cooler waters.
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Abalones
• Source of food and
decoration – the inner
part of the shell is
highly iridescent and
used for mother-ofpearl inlays.
• Cling to rocks in
subtidal zone and
feed on primarily red
algae.
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Slugs
• No shell
• Garden pests
• Bodies are prone to
desiccation –
confined to moist
environments
• Secrete mucous to
help prevent
desiccation and to
protect themselves
against predation.
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Limpets
• Gastropods with
conical shaped shells
• Attach to rocks or
other hard substrates
in intertidal zones.
• Contain gills and
lungs to survive in
intertidal zone.
• May be eaten in
certain parts of the
world.
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Conchs
• Large shell with highly
spiraled character
• All species are marine
• Conchs are found in
the Indian & Pacific
oceans as well as in
the Caribbean sea.
• Their meat is used as
food and their shells
are highly prized as
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decorations.
Class Cephalopoda
Squids, Octopi, Nautiluses
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Class Cephalopoda
• Shell in squid and
octopus absent or
vestigial. Present in
nautilus.
• Movement via jet
propulsion
• Ink sac used for defense
• Foot modified into arms
and tentacles
• All marine and
predatory.
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Squid
Posterior surface
Right
Ventral
Dorsal
Left
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Squid
• Have 8 arms and two
tentacles.
• Siphon allows jet
propulsion in both
directions along the axis
of the animal.
• Swimming fins located
on either side of the
mantle.
• Giant axon is the largest
neuron in the animal
kingdom
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Squid
Tentacle
Arm
Funnel (siphon)
Collar
Eye
Fin
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Squid
Shell (Pen)
Systemic
heart
Branchial heart
Ctenidium
Funnel
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Squid Male
Testis
Penis
Hectocotylous arm
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Squid Female
Ovary with eggs
Oviducal gland
Nidamental glands
Oviducal opening
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Cephalopod Eye
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Octopus
• Eight arms with
suckers
• Crawl or eject water
from siphon
• Change skin color
– chromatophores
• Most intelligent
invertebrate
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Chromatophores
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Nautilus
• Up to 94 tentacles
– No suckers
• Shell with many
chambers – lives in
outermost chamber.
• Considered to be a living
fossil.
• Can alter the amount of
gasses in shell chambers
thus controlling its
position in the water
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column.
Nautilus
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Class Scaphopoda
• Tooth shells
• Shell opens on both
ends
• Burrow into mud
• No gills
– Mantle for gas
exchange
• Feed on detritus and
protozoa
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Class Scaphopoda
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The End
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