Marine Ecology, April 9, 2007

Invertebrates 2: Phylum Mollusca

Phylum Mollusca:The “soft-bodied” animals

Molluscan body plan Hypothetical ancestral mollusc (HAM)

Shell Mantle Mantle cavity Ctenidia Visceral mass Head and

assocated sensory structures

Radula Foot and epipodial

tentacles

Class Polyplacophora: chitons “many plates”

Differences from HAM8 shell platesMantle cavity

expanded around footMultiple ctenidiaMantle grows over

shell, thickened (new functions?)

Reduced head without sensory structures

Phylum Mollusca Class Polyplacophora Cryptochiton stelleri

Phylum Mollusca Class Polyplacophora Katharina tunicata

Phylum Mollusca Class Polyplacophora Tonicella lineata

Phylum Mollusca Class Polyplacophora Mopalia muscosa

Phylum Mollusca, Class Gastropoda: “stomach-foot”

Representative membersLimpets, snails,

abalones, nudibranchs

Diff. from HAMUndergo torsion

What is torsion? Advantages of

torsion Disadvantages of

torsion

Phylum Mollusca, Class Gastropoda

Key: Gastropods undergo torsion!

Phylum MolluscaClass Gastropoda

Diodora aspera

Phylum MolluscaClass Gastropoda Lottia gigantea

Phylum MolluscaClass Gastropoda Collisella digitalis

Phylum MolluscaClass Gastropoda Collisella pelta

Phylum MolluscaClass Gastropoda Tegula funebralis

Phylum MolluscaClass Gastropoda Littorina sp.

Phylum MolluscaClass Gastropoda Nucella sp.

Phylum MolluscaClass Gastropoda Nudibranch (dorid)

Archidoris montereyensis

Phylum MolluscaClass Gastropoda Nudibranch (dorid)

Rostangia pulchra

Phylum MolluscaClass Gastropoda Nudibranch (dorid)

Discodoris (Dialula sandiegensis)

Phylum MolluscaClass Gastropoda Nudibranch (aeolid)

Hermissenda (Phidiana) crassicornis

Class Bivalvia: “two valves”

Representative members: Clams, mussels and scallops

Differences from HAMTwo shellsMantle/sensory structuresExpanded mantle cavityEnlarged ctenidia

Respiration AND feedingReduced headFoot more elongate;

Minimal area for suction

Phylum MolluscaClass Bivalvia Mytilus

californianus Mytilus edulis