Phylum MolluscaPhylum Mollusca

Chitons, Snails, Clams, Chitons, Snails, Clams, Squids, etc.Squids, etc.

Classes of MolluscaClasses of Mollusca

Class Bivalvia (Clams, oysters)Class Bivalvia (Clams, oysters) Class Gastropoda (snails, slugs)Class Gastropoda (snails, slugs) Class Cephalopoda (Squid, octopus)Class Cephalopoda (Squid, octopus) Class Polyplacophora (Chitons)Class Polyplacophora (Chitons) Class Scaphopoda (Tusk shells)Class Scaphopoda (Tusk shells) Additional classes not coveredAdditional classes not covered

Class CaudofoveataClass Caudofoveata Class SolengastresClass Solengastres Class MonoplacophoraClass Monoplacophora

General CharacteristicsGeneral Characteristics

Molluscs inhabit marine, freshwater, and Molluscs inhabit marine, freshwater, and terrestrial habitats.terrestrial habitats.

Body bilaterally symmetrical; Body bilaterally symmetrical; unsegmented; often with a definitive head.unsegmented; often with a definitive head.

Possess a muscular footPossess a muscular foot Possess a specialized tissue – MantlePossess a specialized tissue – Mantle Secretes the shell aids in Respiration, Secretes the shell aids in Respiration,

reproduction etc.reproduction etc.

Visceral mass contains all major organ systemsVisceral mass contains all major organ systems Complex digestive system; rasping organ Complex digestive system; rasping organ

(radula)(radula) Open circulatory systemOpen circulatory system Respiratory pigment is hemocyaninRespiratory pigment is hemocyanin Nervous system consists of paired gangliaNervous system consists of paired ganglia Well developed sense organs (eyes in Well developed sense organs (eyes in

cepahlopods)cepahlopods) Sexes are separate – larval stages in some Sexes are separate – larval stages in some

(Veliger, Glochidium)(Veliger, Glochidium)

General Characteristics General Characteristics cont.cont.

Archetype Molluscan BodyArchetype Molluscan Body

RadulaRadula

Mantle and Shell LayersMantle and Shell Layers

Class - Bivalvia Class - Bivalvia (Pelecypoda)(Pelecypoda)

Clams, Mussels, Oysters, etcClams, Mussels, Oysters, etc

General CharacteristicsGeneral Characteristics

Body enclosed in mantleBody enclosed in mantle shell has two lateral valves with dorsal hingeshell has two lateral valves with dorsal hinge Umbo – oldest part of shellUmbo – oldest part of shell Head greatly reducedHead greatly reduced No radulaNo radula No eyes, a few species with eyes on mantle No eyes, a few species with eyes on mantle

marginmargin foot usually wedge-shapedfoot usually wedge-shaped

Figure 16.31aFigure 16.31a

Figure 16.31bFigure 16.31b

Clam DissectionClam Dissection

Glochidium Glochidium larva larva

and mantle and mantle lure lure

of female freshof female freshwater musselwater mussel

Class GastropodaClass Gastropoda

SnailsSnails

General CharacteristicsGeneral Characteristics

Body usually asymmetrical with a coiled Body usually asymmetrical with a coiled shell (torsion)shell (torsion)

Some species lack shell and are not Some species lack shell and are not coiledcoiled

Head well-developedHead well-developed Radula presentRadula present Mantle modified into a lung or gillMantle modified into a lung or gill Foot large and flatFoot large and flat

Figure 16.12Figure 16.12

Figure 16.18Figure 16.18

RadulaRadula

Some GastropodsSome Gastropods

HelixHelix – garden snail – garden snail

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Class CephalopodaClass Cephalopoda

Squids, Cuttlefish, Chambered Squids, Cuttlefish, Chambered Nautilus, and OctopusesNautilus, and Octopuses

General CharacteristicsGeneral Characteristics

Shell often reduced or absentShell often reduced or absent Head well developed with a modified Head well developed with a modified

radula to form a beakradula to form a beak Foot modified into arms and/or Foot modified into arms and/or

tentaclestentacles Nervous system with centralized brainNervous system with centralized brain Complex, well-developed eyesComplex, well-developed eyes

Squid DissectionSquid Dissection

Some CephalopodsSome Cephalopods

Chambered NautilusChambered Nautilus

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CuttlefishCuttlefish

SquidSquid

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Class PolyplacophoraClass Polyplacophora

The ChitonsThe Chitons

General CharacteristicsGeneral Characteristics

Elongated, dorsoventrally flattened Elongated, dorsoventrally flattened Reduced headReduced head Bilaterally symmetricalBilaterally symmetrical Radula presentRadula present Shell of eight dorsal plates Shell of eight dorsal plates Foot broad and flatFoot broad and flat Multiple gills, along sides of body Multiple gills, along sides of body

between foot and mantle edgebetween foot and mantle edge

ChitonsChitons

Class ScaphopodaClass Scaphopoda

Tusk ShellsTusk Shells

General CharacteristicsGeneral Characteristics

Body enclosed in a one-piece tubular Body enclosed in a one-piece tubular shell open at both endsshell open at both ends

Conical footConical foot Mouth with radula and tentaclesMouth with radula and tentacles Head absentHead absent Mantle used for respirationMantle used for respiration

Figure 16.11aFigure 16.11a

Tooth or Tusk ShellsTooth or Tusk Shells