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Phylum Mollusca
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Molluscan diversity
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PoriferaPoriferaCycliophoraCycliophora CnidariaCnidaria CtenophoraCtenophora SipunculaSipuncula MolluscaMollusca AnnelidaAnnelida OnychophoraOnychophora TardigradaTardigrada BryozoaBryozoa PlatyhelminthesPlatyhelminthes NemerteaNemertea RotiferaRotifera GnathostomulidaGnathostomulida GastrotrichaGastrotricha NematodaNematoda NematomorphaNematomorpha PriapulidaPriapulida KinorhynchaKinorhyncha LoriciferaLoricifera PhoronidaPhoronida BrachiopodaBrachiopoda EchinodermataEchinodermata ChordataChordata HemichordataHemichordata ArthropodaArthropoda Adapted from Lesser Known Protostome Phyla. SICB 2001. J.R. Garey. Possess trochophore larvae Mollusca and Annelida are closely allied phyla
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93,000 species of described molluscs (extant) + 70,000 more species from fossil record Echinodermata Ciliophora Chordata Mollusca Platyhelminthes Nematoda Porifera Annelida Other Apicomplex Sarcomastigophora Arthropoda
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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
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Phylum. Mollusca Class. Aplacophora Class. Polyplacophora Class. Monoplacophora Class. Gastropoda Class. Cephalopoda Class. Bivalvia Class. Scaphopoda Phylum. Mollusca Class. Aplacophora Class. Polyplacophora Class. Monoplacophora Class. Gastropoda Class. Cephalopoda Class. Bivalvia Class. Scaphopoda
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Aplacophora Polyplacophora Monoplacophora Gastropoda Cephalopoda Bivalvia Scaphopoda
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Mollusc origins? Platyhelminthe-like ancestor with spicules on dorsal surface, cilia on ventral surface, and dorsoventral musculature.
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Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, and dorsoventral musculature.
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Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads and excretory pores in mantle cavity
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Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads, excretory pores, and ctenidia, in mantle cavity.
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HAM: Hypothetical ancestral mollusc Mantle cavity CtenidiumCtenidium Pericardial cavity MetanephridiumMetanephridium RadulaRadula GonadGonad Stomach and digestive gland FootFoot
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Dorsal mantle covers the visceral mass. Secretes the shell
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Mollusc shell PeriostracumPeriostracum Prismatic layer Nacreous layer Mantle epithelium Mantle lobes
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Pearl formation PeriostracumPeriostracum Prismatic layer Nacreous layer Developing pearl EpitheliumEpithelium
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Ctenidium (Respiration)
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Ctenidium (gill) InterlamellarjunctionsInterlamellarjunctions OstiumOstium FrontalciliaFrontalcilia Blood vessel ExhalentwaterExhalentwater
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Paired ventral nerve cords
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Complete digestive system
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Radula
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Aplacophora Gill folds MouthMouth Pedal pit Pedal groove
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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
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Polyplacophora
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Mantle cavity MouthMouth CtenidiumCtenidium FootFoot AnusAnus
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Polyplacophora MouthMouth DigestiveglandDigestivegland StomachStomachGonadGonad Pericardial cavity NephridiumNephridium AnusAnus
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Polyplacophora The “chitons” 800 spp, marine Typically, shell = 8 dorsal plates Ctenidia use counter-current gas exchange Commonly encountered in the intertidal zone
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