1、Phylum MolluscaMolluscan diversityMollusca and Annelida are closely allied phyla 93,000 species of described molluscs(extant)+70,000 more species from fossil recordEchinodermataCiliophoraChordataMolluscaPlatyhelminthesNematodaPoriferaAnnelidaOtherApicomplexSarcomastigophoraArthropodaDefining charact
2、eristics 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),kidneyAplacophoraPolyplacophoraMonoplacophoraGastro
3、podaCephalopodaBivalviaScaphopodaMollusc 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 t
4、o form dorsal shell,cilia on ventral surface,dorsoventral musculature,gonads and excretory pores in mantle cavityMollusc origins?Spicules fuse to form dorsal shell,cilia on ventral surface,dorsoventral musculature,gonads,excretory pores,and ctenidia,in mantle cavity.HAM:Hypothetical ancestral mollus
5、cDorsal mantle covers the visceral mass.Secretes the shellMollusc shellPearl formationCtenidium(Respiration)Ctenidium(gill)Paired ventral nerve cordsComplete digestive systemRadulaRadulaAplacophoraClass 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 cnidariansPolyplacophoraPolyplacophoraPolyplacophoraPolyplacophora The“chitons”800 spp,marine Typically,shell=8 dorsal plates Ctenidia use counter-current gas exchange Commonly encountered in the intertidal zone
