Phylum MolluscaPhylum Mollusca

Molluscan diversityMolluscan diversity

PoriferaPoriferaPoriferaPorifera

CycliophoraCycliophoraCycliophoraCycliophora

CnidariaCnidariaCnidariaCnidariaCtenophoraCtenophoraCtenophoraCtenophora

SipunculaSipunculaSipunculaSipunculaMolluscaMolluscaMolluscaMolluscaAnnelidaAnnelidaAnnelidaAnnelida

OnychophoraOnychophoraOnychophoraOnychophoraTardigradaTardigradaTardigradaTardigrada

BryozoaBryozoaBryozoaBryozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthes

NemerteaNemerteaNemerteaNemertea

RotiferaRotiferaRotiferaRotifera

GnathostomulidaGnathostomulidaGnathostomulidaGnathostomulidaGastrotrichaGastrotrichaGastrotrichaGastrotricha

NematodaNematodaNematodaNematodaNematomorphaNematomorphaNematomorphaNematomorpha

PriapulidaPriapulidaPriapulidaPriapulidaKinorhynchaKinorhynchaKinorhynchaKinorhynchaLoriciferaLoriciferaLoriciferaLoricifera

PhoronidaPhoronidaPhoronidaPhoronidaBrachiopodaBrachiopodaBrachiopodaBrachiopoda

EchinodermataEchinodermataEchinodermataEchinodermata

ChordataChordataChordataChordataHemichordataHemichordataHemichordataHemichordata

ArthropodaArthropodaArthropodaArthropoda

Adapted from Lesser Known ProtostomeAdapted from Lesser Known ProtostomePhyla. SICB 2001. J.R. Garey. Phyla. SICB 2001. J.R. Garey.

Possess trochophore larvaePossess trochophore larvae

Mollusca and Annelida are closely allied phyla

93,000 species of described molluscs (extant) + 70,000 more species from fossil record93,000 species of described molluscs (extant) + 70,000 more species from fossil record

Echinodermata

Ciliophora

Chordata

Mollusca

Platyhelminthes

Nematoda

PoriferaAnnelida

Other

Apicomplex

Sarcomastigophora

Arthropoda

Defining characteristics of Mollusca• Bilateral symmetry, cephalization• Coelom (around heart)• Mantle

– draped over viscera– secretes shell

• Complete digestive tract, Radula • Trochophore larvae (often also veliger larvae)• Locomotion by muscular foot• Heart, liver, gills (ctenidia), kidney

Phylum.Phylum. Mollusca MolluscaClass.Class. Aplacophora Aplacophora

Class.Class. Polyplacophora Polyplacophora

Class.Class. Monoplacophora Monoplacophora

Class.Class. Gastropoda Gastropoda

Class.Class. Cephalopoda Cephalopoda

Class.Class. Bivalvia Bivalvia

Class.Class. Scaphopoda Scaphopoda

Phylum.Phylum. Mollusca MolluscaClass.Class. Aplacophora Aplacophora

Class.Class. Polyplacophora Polyplacophora

Class.Class. Monoplacophora Monoplacophora

Class.Class. Gastropoda Gastropoda

Class.Class. Cephalopoda Cephalopoda

Class.Class. Bivalvia Bivalvia

Class.Class. Scaphopoda Scaphopoda

Aplacophora Polyplacophora Mon

opla

coph

ora

Gas

tropo

daCep

halo

poda

Bivalvia Scaphopoda

Mollusc origins?

Platyhelminthe-like ancestor with spicules on dorsal surface, cilia on ventral surface, and dorsoventral musculature.

Mollusc origins?

Spicules fuse to form dorsal shell, cilia on ventral surface, and dorsoventral musculature.

Mollusc origins?

Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads and excretory pores in mantle cavity

Mollusc origins?

Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads, excretory pores, and ctenidia, in mantle cavity.

HAM: Hypothetical ancestral molluscHAM: Hypothetical ancestral mollusc

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

Dorsal mantle covers the visceral mass.

Dorsal mantle covers the visceral mass.

Secretes the shellSecretes the shell

Mollusc shellMollusc shell

PeriostracumPeriostracumPeriostracumPeriostracum

Prismatic layerPrismatic layerPrismatic layerPrismatic layer

Nacreous layerNacreous layerNacreous layerNacreous layer

Mantle epitheliumMantle epitheliumMantle epitheliumMantle epithelium

Mantle lobesMantle lobesMantle lobesMantle lobes

Pearl formationPeriostracumPeriostracumPeriostracumPeriostracum

Prismatic layerPrismatic layerPrismatic layerPrismatic layer

Nacreous layerNacreous layerNacreous layerNacreous layer

Developing pearlDeveloping pearlDeveloping pearlDeveloping pearl

EpitheliumEpitheliumEpitheliumEpithelium

Ctenidium (Respiration)Ctenidium (Respiration)

Ctenidium (gill)Ctenidium (gill)InterlamellarInterlamellarjunctionsjunctionsInterlamellarInterlamellarjunctionsjunctions

OstiumOstiumOstiumOstium

FrontalFrontalciliacilia

FrontalFrontalciliacilia

Blood vesselBlood vesselBlood vesselBlood vessel

ExhalentExhalentwaterwaterExhalentExhalentwaterwater

Paired ventral nerve cordsPaired ventral nerve cords

Complete digestive systemComplete digestive system

RadulaRadula

RadulaRadula

Aplacophora

Gill foldsGill foldsGill foldsGill folds MouthMouthMouthMouth

Pedal pitPedal pitPedal pitPedal pit

Pedal groovePedal groovePedal groovePedal groove

Class Aplacophora

• 320 spp, all marine

• No fossil record (!) & poorly studied

• Calcareous spines and scales in epidermis (no true shell)

• Radula used for grasping

• Burrow in the substrate

• Eat cnidarians

PolyplacophoraPolyplacophora

Polyplacophora

Mantle cavityMantle cavityMantle cavityMantle cavityMouthMouthMouthMouth

CtenidiumCtenidiumCtenidiumCtenidium

FootFootFootFoot

AnusAnusAnusAnus

PolyplacophoraPolyplacophora

MouthMouthMouthMouth

DigestiveDigestiveglandgland

DigestiveDigestiveglandgland

StomachStomachStomachStomach GonadGonadGonadGonadPericardial cavityPericardial cavityPericardial cavityPericardial cavity

NephridiumNephridiumNephridiumNephridium

AnusAnusAnusAnus

Polyplacophora

• The “chitons”

• 800 spp, marine

• Typically, shell = 8 dorsal plates

• Ctenidia use counter-current gas exchange

• Commonly encountered in the intertidal zone