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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

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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MyxozoaMyxozoaMyxozoaMyxozoa

ArthropodaArthropodaArthropodaArthropoda AnnelidaAnnelidaAnnelidaAnnelida

MolluscaMolluscaMolluscaMollusca

LophophoresLophophoresLophophoresLophophores

HemichordataHemichordataHemichordataHemichordata

VertebrataVertebrataVertebrataVertebrata

Other Other pseudocoelomatespseudocoelomates

Other Other pseudocoelomatespseudocoelomates

NematodaNematodaNematodaNematoda

PoriferaPoriferaPoriferaPorifera

CtenophoraCtenophoraCtenophoraCtenophoraCnidariaCnidariaCnidariaCnidaria

PlacozoaPlacozoaPlacozoaPlacozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthesNemerteaNemerteaNemerteaNemertea

CiliophoraCiliophoraCiliophoraCiliophoraSarcomastigophoraSarcomastigophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaMicrosporaMicrosporaApicomplexaApicomplexaApicomplexaApicomplexa

MesozoaMesozoaMesozoaMesozoa

EchinodermataEchinodermataEchinodermataEchinodermata

CrustaceaCrustaceaCrustaceaCrustaceaChelicerataChelicerataChelicerataChelicerata

UniramiaUniramiaUniramiaUniramia

Other ChordataOther ChordataOther ChordataOther Chordata

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Generalized Mollusk

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Body PlanBody Plan

Mantle cavityMantle cavityMantle cavityMantle cavity

CtenidiumCtenidiumCtenidiumCtenidium

Pericardial cavityPericardial cavityPericardial cavityPericardial cavity MetanephridiumMetanephridiumMetanephridiumMetanephridium

RadulaRadulaRadulaRadula

GonadGonadGonadGonad

Stomach and digestive glandStomach and digestive glandStomach and digestive glandStomach and digestive gland FootFootFootFoot

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Dorsal mantle covers the visceral mass.

Dorsal mantle covers the visceral mass.

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Secretes the shellSecretes the shell

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Ctenidium (Respiration)Ctenidium (Respiration)

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Complete digestive systemComplete digestive system

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Paired ventral nerve cordsPaired ventral nerve cords

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RadulaRadula

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Source: From A Life of Invertebrates, Copyright © 1979 W. D. Russell-Hunter.

Radular Structure

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Coelom - metanephridiaCoelom - metanephridia

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Class PolyplacophoraChitons

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Class PolyplacophoraClass 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

Mantle cavityMantle cavityMantle cavityMantle cavityMouthMouthMouthMouth

CtenidiumCtenidiumCtenidiumCtenidium

FootFootFootFoot

AnusAnusAnusAnus

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Class PolyplacophoraClass Polyplacophora

MouthMouthMouthMouth

DigestiveDigestiveglandgland

DigestiveDigestiveglandgland

StomachStomachStomachStomach GonadGonadGonadGonadPericardial cavityPericardial cavityPericardial cavityPericardial cavity

NephridiumNephridiumNephridiumNephridium

AnusAnusAnusAnus

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Class BivalviaClams, Oysters, Mussels, & Scallops

Class BivalviaClams, 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 structuresBivalve structures

IncurrentIncurrentsiphonsiphonIncurrentIncurrentsiphonsiphon

CtenidiumCtenidiumCtenidiumCtenidium

ExcurrentExcurrentsiphonsiphonExcurrentExcurrentsiphonsiphon

HingeHingeHingeHinge

FootFootFootFoot

Labial palpLabial palpLabial palpLabial palp

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Clam anatomyClam anatomyPericardial cavityPericardial cavityPericardial cavityPericardial cavity

HeartHeartHeartHeart

GonadGonadGonadGonadIntestineIntestineIntestineIntestine

StomachStomachStomachStomach IncurrentIncurrentIncurrentIncurrent

ExcurrentExcurrentExcurrentExcurrent

IntestineIntestineIntestineIntestine

MetanephridiumMetanephridiumMetanephridiumMetanephridium

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Clam anatomyClam anatomy

GonadGonadGonadGonadIntestineIntestineIntestineIntestine

StomachStomachStomachStomachIncurrentIncurrentIncurrentIncurrent

ExcurrentExcurrentExcurrentExcurrent

DigestiveDigestiveglandgland

DigestiveDigestiveglandgland

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Clam anatomyClam anatomyPericardial cavityPericardial cavityPericardial cavityPericardial cavity

HeartHeartHeartHeart

IncurrentIncurrentIncurrentIncurrent

ExcurrentExcurrentExcurrentExcurrent

IntestineIntestineIntestineIntestine

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Clam anatomyClam anatomyPericardial cavityPericardial cavityPericardial cavityPericardial cavity

HeartHeartHeartHeart

GonadGonadGonadGonad

IncurrentIncurrentIncurrentIncurrent

ExcurrentExcurrentExcurrentExcurrent

IntestineIntestineIntestineIntestine

MetanephridiumMetanephridiumMetanephridiumMetanephridium

Oysters

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• 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

Vibrio vulnificus

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Pearl formation

Developing pearlDeveloping pearlDeveloping pearlDeveloping pearl

EpitheliumEpitheliumEpitheliumEpithelium

ShellShellShellShell

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 water determines the color of the resulting pearl.

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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

Shipworms

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Class GastropodaSnails, Slugs, Conchs, Abalones, & Limpets

Class GastropodaSnails, 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

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

TentacleTentacle(Eye stalks)(Eye stalks)TentacleTentacle(Eye stalks)(Eye stalks)

TentacleTentacleTentacleTentacle

PneumostomePneumostomePneumostomePneumostome

AnusAnusAnusAnus

FootFootFootFootMouthMouthMouthMouth

Genital poreGenital poreGenital poreGenital pore

ShellShellShellShell

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Internal Structure of a Generalized Gastropod

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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AbalonesAbalones

• 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-of-pearl 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.

Limpets

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• 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 decorations.

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Class CephalopodaSquids, Octopi, Nautiluses

Class CephalopodaSquids, Octopi, Nautiluses

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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SquidSquid

DorsalDorsalVentralVentral

Posterior surfacePosterior surface

RightRight

LeftLeft

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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SquidSquid

FinFinFinFin

ArmArmArmArm

Funnel (siphon)Funnel (siphon)Funnel (siphon)Funnel (siphon)

EyeEyeEyeEye

TentacleTentacleTentacleTentacle

CollarCollarCollarCollar

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SquidSquidShell (Pen)Shell (Pen)Shell (Pen)Shell (Pen)

CtenidiumCtenidiumCtenidiumCtenidium

FunnelFunnelFunnelFunnel

SystemicSystemicheartheartSystemicSystemicheartheart

Branchial heartBranchial heartBranchial heartBranchial heart

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Squid MaleSquid MaleTestisTestisTestisTestis

Hectocotylous armHectocotylous armHectocotylous armHectocotylous arm

PenisPenisPenisPenis

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Squid FemaleSquid Female

Ovary with eggsOvary with eggsOvary with eggsOvary with eggs

Nidamental glandsNidamental glandsNidamental glandsNidamental glands

Oviducal glandOviducal glandOviducal glandOviducal gland

Oviducal openingOviducal openingOviducal openingOviducal opening

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Cephalopod Eye

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 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 ScaphopodaClass Scaphopoda

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The End