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Phylum Mollusca

BIO 2215

Oklahoma City Community College

Dennis Anderson

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Phylum Mollusca

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Numbers of speciesNumbers of species

Echinodermata

Ciliophora

Chordata

Mollusca

Platyhelminthes

Nematoda

PoriferaAnnelida

Other

Apicomplex

Sarcomastigophora

Arthropoda

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Molluscs

• 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 mantle cavity

• Shell• Radula• Coelom

(eucoelomate)• Metanephridia• Open circulatory

system– Closed in cephalopods

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Economics

• Pearls• Burrowing shipworms • Snails & slugs

– Garden pests– Food– Intermediate hosts for

parasites

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Trochophore Larva• Same type as Phylum

Annelida

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MyxozoaMyxozoa

ArthropodaArthropoda AnnelidaAnnelida

MolluscaMollusca

LophophoresLophophores

HemichordataHemichordata

VertebrataVertebrata

Other pseudocoelomates

Other pseudocoelomates

NematodaNematoda

PoriferaPorifera

CtenophoraCtenophoraCnidariaCnidaria

PlacozoaPlacozoa

PlatyhelminthesPlatyhelminthes

NemerteaNemertea

CiliophoraCiliophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaApicomplexaApicomplexa

MesozoaMesozoa

EchinodermataEchinodermata

CrustaceaCrustaceaChelicerataChelicerata

UniramiaUniramia

Other ChordataOther Chordata

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Generalized Mollusc

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Body PlanBody Plan

Mantle cavityMantle cavity

CtenidiumCtenidium

Pericardial cavityPericardial cavity MetanephridiumMetanephridium

RadulaRadula

GonadGonad

Stomach and digestive glandStomach and digestive gland FootFoot

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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• Reduced head• Radula reinforced

with iron– Scrape algae from

rocks

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Class Polyplacophora

Mantle cavityMantle cavityMouthMouth

CtenidiumCtenidium

FootFoot

AnusAnus

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Class PolyplacophoraClass Polyplacophora

MouthMouth

Digestivegland

Digestivegland

StomachStomach GonadGonadPericardial cavityPericardial cavity

NephridiumNephridium

AnusAnus

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Class BivalviaClams, Oysters, Shipworms

Class BivalviaClams, Oysters, Shipworms

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Class Bivalvia

• Two shells• Most are filter feeders• No head or radula• Burrow

– Sand, wood, rocks

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Giant Clam & Burrowing Clam

Siphon

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Zebra Mussel

• Environmental Pest• Ballast water of ships

from Europe in 1986• Attack be 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

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Zebra Mussel

• 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

IncurrentsiphonIncurrentsiphon

CtenidiumCtenidium

ExcurrentsiphonExcurrentsiphon

HingeHinge

FootFoot

Labial palpLabial palp

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Clam anatomyClam anatomyPericardial cavityPericardial cavity

HeartHeart

GonadGonadIntestineIntestine

StomachStomach IncurrentIncurrent

ExcurrentExcurrent

IntestineIntestine

MetanephridiumMetanephridium

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Clam anatomyClam anatomy

GonadGonadIntestineIntestine

StomachStomachIncurrentIncurrent

ExcurrentExcurrent

Digestivegland

Digestivegland

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Clam anatomyClam anatomyPericardial cavityPericardial cavity

HeartHeart

IncurrentIncurrent

ExcurrentExcurrent

IntestineIntestine

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Clam anatomyClam anatomyPericardial cavityPericardial cavity

HeartHeart

GonadGonad

IncurrentIncurrent

ExcurrentExcurrent

IntestineIntestine

MetanephridiumMetanephridium

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Oysters

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Pearl formation

Developing pearlDeveloping pearl

EpitheliumEpithelium

ShellShell

Irritant lodged between shell and mantle

Layers of nacre secreted around foreign material

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Scallops

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Shipworms

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Class GastropodaSnails, Slugs, Conchs, Limpets

Class GastropodaSnails, Slugs, Conchs, Limpets

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Class Gastropoda

• One shell (if present)• Torsion of body

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Snail

• Terrestrail• Mantle cavity

functions as lung

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Snail

Tentacle(Eye stalks)Tentacle(Eye stalks)

TentacleTentacle

PneumostomePneumostome

AnusAnus

FootFootMouthMouth

Genital poreGenital pore

ShellShell

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

Internal Structure of a Generalized Gastropod

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Nudibranch

• No shell• Dorsal projections

– Gills– Nematocyst discharge

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AbaloneAbalone

• Several holes in top of shell– Excrete waste

• Food for man

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Slug

• No shell• Garden pests

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Limpet

• Herbivores• Cling to rocks or other surfaces

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Conch

• Large shell• Marine• Many are predators

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Class CephalopodaSquids, Octopuses, Nautiluses

Class CephalopodaSquids, Octopuses, Nautiluses

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Class Cephalopoda

• Shell in squid and octopus absent or vestigial

• Jet propulsion• Ink sac• Foot modified into

arms and tentacles• Marine• All predators

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SquidSquid

DorsalVentral

Posterior surface

Right

Left

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SquidSquid

FinFin

ArmArm

Funnel (siphon)Funnel (siphon)

EyeEye

TentacleTentacle

CollarCollar

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SquidSquidShell (Pen)Shell (Pen)

CtenidiumCtenidium

FunnelFunnel

SystemicheartSystemicheart

Branchial heartBranchial heart

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Squid MaleSquid MaleTestisTestis

Hectocotylous armHectocotylous arm

PenisPenis

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Squid FemaleSquid Female

Ovary with eggsOvary with eggs

Nidamental glandsNidamental glands

Oviducal glandOviducal gland

Oviducal openingOviducal opening

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

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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Nautilus

• Up to 94 tentacles– No suckers

• Shell with many chambers– Lives in outermost

chamber

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Ammonoids

• Extinct• Devonian to

Cretaceous– 400 to 65 MYA

• Died out with dinosaurs

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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 ScaphododaClass Scaphododa

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The End