Phylum Mollusca “soft bodied” animalsMollusca CharacteristicsHAM(Hypothetical Ancestral Mollusc)Mollusca CharacteristicsMollusca CharacteristicsMollusca CharacteristicsMollusca CharacteristicsMollusca CharacteristicsMollusca CharacteristicsMollusca CharacteristicsMolluscan RadiationHAM(Hypothetical Ancestral Mollusc)Molluscan RadiationPhylum MolluscaClass Gastropodasnails and slugsTorsionCoilingClass GastropodaClass GastropodaSubclass ProsobranchiaClass GastropodaSubclass ProsobranchiaClass GastropodaSubclass OpisthobranchiaDetorsionClass GastropodaSubclass OpisthobranchiaClass GastropodaSubclass OpisthobranchiaClass Gastropoda Subclass OpisthobranchiaClass Gastropoda Subclass OpisthobranchiaClass GastropodaSubclass PulmonataClass Bivalvia(class Pelecypoda)the “bivalves”Class BivalviaClass Cephalopodathe squids, octopus, nautilus, and cuttlefishClass CephalopodaClass CephalopodaClass CephalopodaClass CephalopodaClass CephalopodaClass CephalopodaClass Polyplacophorathe “chitons”Class PolyplacophoraClass Scaphopodathe “tusk shells”Class ScaphopodaAnnelidaMolluscaArthropodaEchinodermataChordataPlatyhelminthesNematodaacoelomatepseudocoelomateseucoelomatesRotiferaprotostomesPhylum Mollusca“soft bodied”animalsMollusca CharacteristicsBody Plan• head-foot: contains sensory organs and muscles• visceral mass: contains digestive, reproductive, circulatory organs• mantle: skin of the dorsal body wall secretes the shell (if there is one), cavity contains gills or lungsshellfootVisceral massmantlemantle cavityperiostracum: conchiolinprismatic layer: calcium carbonatenacreous layer: calcium carbonate and proteinsmantleHAM(Hypothetical Ancestral Mollusc)Digestive glandMouthRadulaNerve collarIntestineGillAnusNephridiumShellMantleNerve cordsfootcoelomheartgonadsheadMollusca CharacteristicsFeeding and Digestion:There are both free living and parasitic formsMost species use a tongue like organ called a radula when feedingodontophoreodontophoreprotractorradularadula retractorradula protractoresophagusodontophore retractorMollusca CharacteristicsFeeding and Digestion:Mollusca CharacteristicsDigestive System• complete with regional specializationanusintestinestomachdigestive glandMollusca CharacteristicsGas Exchange• mainly gills, however terrestrial species have evolved lungs axisafferent blood vessel: into gillwaterefferent blood vessel: out of gillMollusca CharacteristicsGas Exchangefootgill gillfootgillMollusca CharacteristicsCirculatory System• open circulatory system (in most classes)• heart and blood sinusesheartcoelomMollusca CharacteristicsExcretion• most have kidneys (metanephridia)•tubules connecting pericardial cavity (coelom) and nephridioporenephridioporeMollusca CharacteristicsNervous systemnerve ringpedal nerve cordvisceral nerve cordMollusca CharacteristicsReproduction• monoecious and dioecious species exist• usually internal fertilization• indirect development with the presence of a trochophore larva (link to annelids), and in most cases also a veliger larvatrochophoreveligerLampsilis ovataovisacsThe juvenile stages of some bivalves are parasiticGlochidia: larval bivalves that are parasitic on fish gillsovisacsLampsilis ovataSome freshwater bivalves have evolved ways of attracting hosts for their larvae.Some species place their larva in a lure called a superconglutinatehttp://courses.smsu.edu/mcb095f/gallery/L_perovalis/lampsilis_perovalis.htmMolluscan Radiation• There are approximately 128,000 living species in phylum Mollusca (35,000 are extinct)• The great morphological diversity is the result of elaboration on the basic body plan (HAM)HAM(Hypothetical Ancestral Mollusc)Digestive glandMouthRadulaNerve collarIntestineGillAnusNephridiumShellMantleNerve cordsfootcoelomheartgonadsheadMolluscan RadiationHAMCephalopoda• lobed foot• highly developed head• shell reduced or lostPolyplacophora• shell consists of 8 platesGastropoda• torsion• coiling of the shellScaphopoda• ventral shell fusionBivalvia• bivalved shell • dorsal hingePhylum MolluscaClass GastropodaClass BivalviaClass CephalopodaClass PolyplacophoraClass ScaphopodaClass Gastropodasnails and slugsTorsion• twisting of the visceral mass through a 180° rotation•1st90° rotation usually occurs at the veliger stage •the 2nd90° rotation usually takes longer and occurs later• after torsion, the anus and mantle cavity end up over the head• this poses a serious fouling problem and many gastropods have lost their right gills, kidneys and heart auricles mouthmouthanusanusanusgillsgillsgillsLarval torsionanusmouthCoilingApex of shell extends out making the shell more compactPlanospiral shellConispiral shellShell shifts over body for betterweight distributionClass GastropodaSubclass ProsobranchiaSubclass OpisthobranchiaSubclass PulmonataClass GastropodaSubclass Prosobranchia• aquatic snails (marine and freshwater)• have undergone torsion and most have undergone shell coiling• have gills• all have shells • use radula for feeding; can be herbivores, carnivores, or detritivoresIn some, mantle extends over shellClass GastropodaSubclass Prosobranchia• snails often lay eggs in protective capsulesClass GastropodaSubclass Opisthobranchia• sea hares and sea slugs (nudibranchs)• have undergone detorsion• have gills• sea hares have a reduced shell • sea slugs have no shellDetorsionmouthanusgillsThey are missing the right gill, kidney and heart auricleClass GastropodaSubclass Opisthobranchia• sea hares and sea slugs (nudibranchs)Class GastropodaSubclass Opisthobranchia• they usually crawl along the bottom but many can also swim by using their modified mantle as “wings”Class GastropodaSubclass Opisthobranchia• all are monoecious• sea hares often form “mating chains”acts as male onlyact as both males and females simultaneouslyacts as female onlyClass GastropodaSubclass Opisthobranchia• sea slugs often lay “ribbons” of eggs which stick to the substrateClass GastropodaSubclass Pulmonata• land snails and land slugs • have lungs• land slugs have undergone detorsion and have lost their shellClass Bivalvia(class Pelecypoda)the “bivalves”Class Bivalvia• clams, mussels, oysters, scallops • use gills for respiration and filter feeding • shell is modified into a bivalved shell connected by muscles and ligaments• no head (reduced sensory organs), no radula• foot can be modified for diggingdorsalumbo-the oldest part of the
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