Mollusca Phylum 100 000 species 70 000 extinct clams snails octopus squid bilateral symmetry coelom limited nephridia heart GI hemocoel open circulatory system a blood sinus visceral mass gut and other organs mantle mantle cavity has shell glands calcerious calcium based ctenidia gills comb like osphradia patch chemo sensor nephridiopores openings to outside from netophridia gonopores opening to outside from gonads anus shell pericardial chamber heart in this chamber see reduced coelom there separate ventral atria large muscular foot flat buccal region radula scrapping feeding device complete GI gut regionally specialized ceca metanephridia complicated protostome development trochophore larva then veliger stage Diagram Classes Apalcophora Monoplacophora Gastropoda Bivalvia Scaphopoda Cephalopoda Polyplacophora Or Chiton 1 Nautiloidea 2 Coeloidea Subclasses Groups Unique Characteristics NOT a solid calcium shell Proscobranchia shelled marine Opisthobranchs marine slugs Pulmonates terrestrial snails slugs Protobranchia pair simple ctenidia Lamellibranchia ctenidia with long filaments Anomalodesmata modified torsion no gills no heart Characteristics Lives at the bottom of the seas bermiform worm like marine shell less spicules rudimentary mc not well developed foot no eyes tentacles statocysts crystalline style nephridia deep sea single cap like shell 8 pairs of retractor muscles disc foot repetitive arrangement shallow mc around foot under shell contains gills can be many up to 7 pair of netaphridia most are extinct single cap like shell flat elongate 1 000 species marine broad ventral foot 8 dorsal shell plates Mc encircles foot multiple gills No eyes tentacles crystalline style No ganglia except buccal 70 000 species Single spirally coiled shell Forms columella head protrudes Dextral coliing Torsion not coling Muscular foot Statocyst eyes tentacles Radula crystalline style Marine 20 000 species Laterally compressed 1 Shell 2 valves hinged dorsally no eyes no radula 1 pair large ctenidia Foot is laterally compressed Labial palps Large mc 1 000 species One piece shell Head rudimentary No ctenidia eyes Have radula proboscis crystalline style Captacula contractile used in feeding No heart vessels Spacious body cavity Closed circulatory system Chambered shell reduced or lost Arms tentacles circle around mouth Radula beak 1 pair of ctenidia External Anatomy shell less calcareous spicules 8 dorsal shell plates One piece shell tubular tapering open at both ends Chambered shell reduced or lost 1 Shell 2 valves hinged dorsally Hinged ligament that holds 2 valves together hinge teeth keep them lined up Head rudimentary no eyes no radula Single spirally clockwise coiled shell cavity Columella running up the shell Spire whorls apterture brought by tors Statocyst eyes tentacles Forms columella end whires apterture head protrudes bilateral symm Body Plans Regions no eyes tentacles statocysts crystalline style nephridia with radula and small head no eyes tentacles only around mouth flat elongate No eyes tentacles head rudimentary Large complex eyes Radula beak water NOT moved by cilia Body Cavity Symmetry The bilateral symm rudimentary mc bilateral symm shallow mc bilateral symm Mc encircles foot bilateral symm large pair bilateral symm Mc large bilateral symm Large ventral mc Mantle Cavity around foot under shell multiple gills cavities siphon Body Wall Support not well developed foot Locomotion ciliary gliding not a well developed foot 8 pairs of retractor muscles Feeding Diegstion crystalline style extending along entire ventral surface Mantle cavity extents entire body Water moved in out of posterior end of mc mantle forms Muscular siphon can direct the jet of water propels them in any direction burrow bivalves predators expel water from mantle cavity through siphon selective deposit feeders Active predators Radula beak mantle cavity area of oxygen exch no gills or ctenidia open cir system Closed circ system 1 pair of ctenidia complex system torsion Muscle contraction waves change shape of bottom of foot radula crystalline style part of digestive tract shell closed by Adductor muscle bladelike and laterally compressed burrowing hemolyph fluid Microphagous or suspension feeders Large gill used in feeding lost radula and head use large ctenidia Prosobranchs deposit feeders 1 pair ctenidia respiration Circulatory System Pouch posterior to pericardial chamber Gas Exchange Excretion Nervous System no nephridia up to 7 pair of netaphridia no statocysts eyes tentacles figure 8 out of cords as a result fusion resulting in 3 ganglia no eyes tentacles or osphradia Complex NS mass of ganglia Reproduction and Development No ganglia except buccal have subradular aesthete sense organs on mantle egde of torsion tentacles and chemical receptors slipper shell female bottom hermaphrodites pulmonates simultaneous her cephilized suckers have statocyst tactile chromatophores chemorecceptor complex spermataphore transfer to fem male uses hectotylous arm female dies no trocophore larva