Phylum Mollusca

= mollis = softBilateral symmetry,secondarily assymetrcial=> Soft bodied animalsCoelomate and triploblastic

Rich fossil record

Next to arthropods, largestand most diverseAdaptive body plan

Shell etc. secreted by mantle

General Molluscan Characteristics

Thick cuticular-epidermalmantle

Heart in pericardial chamber

Radula

Complete gut

Microscopic to 20 mGiant octopus = 40kg

General Molluscan Characteristics

General Molluscan Bauplan= hypothetical ancestral molluscMolluscs can be derived from single model=> incorporates diagnostic featuresReduced coelom = hemocoel

protostyle bipectinate ctenidia = respiration/feeding radula/odontophore complex thick epidermal mantle

A. Head-Foot B. Visceral Mass/Hump C. Mantle/Pallium

Shell

Periostracum Thin layer of organic coating = conchiolin or conchin Prismatic 1 of 2 calcium carbonate

layers (calcite or argonite)Nacreous or mother of pearlAragonite arraged in parallel lamina, elastic bipolimers(chitin, lustrin and silk-like proteins)

Periostracum and prismatic = secreted by specializedperipheral mantle cellsNacreous = secreted by majority of mantle

Bodywall

Composed of1. CuticleAmino acids &Sclerotinizedproteins= conchin2. EpidermisSingle layerCuboidal or columnar, ciliatedSecrete cuticle, shell other glandular function not known3. Muscle layer3 distinct layers = circular, diagonal and longitudinal

Nutrition and Feeding= tremendous variation

(A) Grazers = gastropods/polyplacophora

Patella = epiphytes/epizooites,radula and mucus laden stringKatherina = subradular organbuccal cavity, mucus

(B) Herbivores = gastropodsLarge aquatic/terrestrial plants, crop/gizzard adaptations(C) CarnivoresAplacophora = cnidarian dietGastropoda = radula modified or proboscisBusycon/Fasciolaria = whelks,Urosalpinx/Lunatia = drillersBivalves = muscular septa, Cephalopods = beak

Nutrition and Feeding(D) Scavengers/Deposit Feeders = Aplacophora, Gastropods,BivalvesStrombus = proboscis, vacuum cleaner(E) Suspension Feeders = Gastropods,ScapopodsCrepidula = lengthened gills, food trappingPteropods = mucus net, scaphopods = captacula(F) Filter Feeders = BivalvesLengthened and folded gill filaments,plankton sieved out by gills(G) Parasites = Gastropods, BivalvesEcoparasites = suck blood with pharynx, endoparasites =sucking porboscis, in echinoderms (Holothuroids)Entovalva = endoparasite, in holothuroid gut

Digestive System

Complete gut, hollow tube= separate mouth/anusSome regional specialization= highest degree incephalopodsDigestive glands or caecae= digestive enzymesMost digestion intracellularSome extracellular= stomach and digestive caecae=> the higher evolved the moreextracellular

Osmoregulation/Excretion/Circulation

Metanephridia = paired, called kidneys, # of pairs varies-> nephrostome -> pericardium -> nephridiophore, wasteHemolymph = open versus closed, heart& body wallpropulsion

ReproductionSexual, asexual is rare(A)Dioecious/ GonochoristicSeparate sexes in most molluscsChitons, bivalves, cephalopods(B) Sequential HermaphroditeProtandric = Gastropodsmale first, then femaleCrepidula fornicata= functional male - body size -option to become female=>depend on population structure(C) Simultaneous HermaphroditesBoth sexes in 1 animal = ovotestesHelix = courtship, spicules,determine male/female roles

DevelopmentCleavage spiral (exceptionCephalopods = meroblastic)Typical larva = trochophoreMost extreme metamorphosis(A)Indirect = Bivalve, Gastropodstrochophore - veliger (foot/shell)Free swimming or parasitic, velumGlochidia = fw bivalves, on gills, nomouth/anus, phagocytosis(B) Mixed = polyplacophora,scaphopodatrochophore - immature adult(C) Direct = CephalopodsLarge, yolky, telolecithal eggsMiniature adult

Nervous System and Sense OrgansCircumenteric ganglia, pairedventral ncMost: cerebral, pleural, pedal,visceral, buccalns development = activityGiant nerve fibers(A)Osphradium = Sensory epitheliumChemoreceptors, sediment monitorBenthic predators, scavengers(B) Cephalic tentacles = 1 pairMay bear eyes/chemoreceptors(C) Rhinophores = chemoreceptors(D) Eyes = from primitive to evolved(E) Statocysts = mobile animals(F) Aesthetes = polyplacophoraphotoreceptors

(A) Hard surface dwellers = bivalvesgastropods, polyplacophorans1. AttachedCrassostrea = cement glandsMytilus = byssus threads! Reduced foot, sense organs2. Unattached3. Boring = bivalves, e.g. Teredo(B) Soft substrate dwellers= gastropods, bivalves, scaphopodsPolinices large foot like ploughStrombus operculum digs into sand(C) Swimmers = Cephalopods,gastropods, bivalvesPtereopods = foot modified

Ecology/Lifestyles

Ecology/Lifestyles(C) Swimmers (cont.)Scallops = adductorcontractionCephalopods = mantle, jetpropulsionfunnel(D) Floaters = GastropodsJanthina = raft of bubblesGlaucus = bubble in stomach(E) Parasites = Gastropods,BivalvesReduced locomotion, sensory! not typicalHigh degree of economic andecological importance

http://www.youtube.com/watch?v=_2iXHBuSIJY

Molluscan TaxonomyAplacophoa

Monoplacophora

Polyplacophora= Amphineura

Scaphopoda

Gastropoda

Bivalvia

Cephalopoda

Class Aplacophora= bearing no shell< 300 species describedSolenogasters, i.e.ChaetodermaVermiform, cylindricalCalcareous spiculesRudimentary mantle cavityCtenidia (gills) not alwaysfoundFoot represented by pedalgroveMay not represent truemollusks

Class Monoplacophora= bearing one shell11 species describedThought to be extinct until1957, good fossil record< 3cm in lengthMostly deep sea animalsexample Neopilina

Class Polyplacophora= bearing many shellsChitonsExamples Ischnochiton,Mopalia, KatherinaAbout 300 described speciesFalttened, elongated8 overlapping shells, uniquearticulation = greek tunicTegumentum (conchiolin,spicules)No eyes/tentaclesMarine, rocky intertidalHoming behavior = homing scars

Class Gastropoda= stomach footSnails and slugs40-75,000 living speciesAdaptive radiation = all habitatsAsymmetricalSpirally coiled shell, singleTorsion(A) Prosobranchia, i.e. HaliotisMarine snails, operculum, gills(B) Opisthobranchia, i.e. AplysiaSeaslugs, shell lost(C) Pulmonata, i.e. Helix/LimaxLand snails, slugsLungs, detorted, no larval stage

= 2-shelled, hatchet footOver 7000 living speciesLaterally compressed2 valves, hingedAbsence of head, radula,

sensory structuresMarine & freshwater(A)Protobranchia, i.e. NuculaSimple ctenidia, marine, deep(B) Lamellibranchia, i.e. OstreaFreshwater & marine, singlectenidium, byssus(C) Anomalodesmata, i.e.Pandora, equivalved shells,marine, carnivorous

Class Bivalvia (Pelecypoda)

= spade footTusk shells, e.g. Cadulus350 species1 shell, tubular, tapering, openat both endsNo ctenidia or eyesCaptacula = clubbed contractileTentaclesNo heart/ circulatory systemburrowers

Class Scaphopoda

= head foot650 living speciesShell reduced or lostHead large/complex eyesClosed circulationMuscular funnel = jetPropulsionBenthic or pelagic, marineBehaviorally complex(A) Subclass Nautiloideai.e. Argonauta, 80-100tentacles, no ink sac,Chromatophores(B) Subclass Coleoidea8-10 arms, eyes, statocystChromatophores, ink sac

Class Cephalopoda