Invertebrates 3Invertebrates 3

Phylum Annelida Phylum Annelida

and Phylum Molluscaand Phylum Mollusca

Branchpoints: Branchpoints:

Pseudocoelomate Pseudocoelomate vs. coelomatevs. coelomate

Protostomes vs. Protostomes vs. deuterostomesdeuterostomes

Aceolomates, Pseudocoelomates Aceolomates, Pseudocoelomates and Coelomatesand Coelomates

PseudocoelomPseudocoelom CoelomCoelom

Surface area for Surface area for nutrient absorption nutrient absorption and gas exchange and gas exchange

++ ++

Larger organsLarger organs ++ ++

Fluid cushions/ Fluid cushions/ protects organsprotects organs

++ ++

Hydrostatic skeleton Hydrostatic skeleton is possibleis possible

++ ++

Completely lined by Completely lined by mesoderm mesoderm

-- ++

Mesenteries suspend Mesenteries suspend internal organsinternal organs

-- ++

Independent Independent movement of gut?movement of gut?

-- ++

Protostomes vs. Protostomes vs. deuterostomesdeuterostomes

Fig 32.7

Major Protostome Phyla Major Protostome Phyla (traditional phylogeny) (traditional phylogeny) Phylum AnnelidaPhylum Annelida Phylum MolluscaPhylum Mollusca Phylum ArthropodaPhylum Arthropoda

Phylum Annelida:Phylum Annelida:The segmented wormsThe segmented worms

Basic Annelida featuresBasic Annelida features

Have all features of coelomates and Have all features of coelomates and protostomes (know!)protostomes (know!)

Have body segmentation (new feature)Have body segmentation (new feature) Repetition of body partsRepetition of body parts Similar structures found in each regionSimilar structures found in each region Some specialization of regionsSome specialization of regions Some continuous parts (digestive system)Some continuous parts (digestive system)

Body Plan (earthworm)Body Plan (earthworm) Digestive systemDigestive system

CompleteComplete Specialized regionsSpecialized regions

CirculationCirculation Closed systemClosed system Multiple heartsMultiple hearts

Gas exchangeGas exchange Body surfaceBody surface CoelomCoelom

ExcretoryExcretory MetanephridiaMetanephridia

Body Plan (cont.)Body Plan (cont.) Nervous systemNervous system

Cerebral ganglia Cerebral ganglia (brain)(brain)

Ventral nerve cord Ventral nerve cord (fused pair of cords)(fused pair of cords)

One ganglion per One ganglion per segmentsegment

MovementMovement PeristalsisPeristalsis SetaeSetae

Annelid diversityAnnelid diversity EarthwormsEarthworms

Marine segmented Marine segmented wormsworms

LeechesLeeches

See previous diagrams

Feeding in different classesFeeding in different classes EarthwormsEarthworms

Earth suckers (create vacuum by expanding muscular Earth suckers (create vacuum by expanding muscular pharnyx); lots left undigestedpharnyx); lots left undigested

Process 40 tons of soil/acre of earth/year!Process 40 tons of soil/acre of earth/year! improve aeration/drainageimprove aeration/drainage

LeechesLeeches Create vacuum by expanding pharynx, digestive tractCreate vacuum by expanding pharynx, digestive tract Blood suckers hang on with suckers, feed with jaws or Blood suckers hang on with suckers, feed with jaws or

have pharynx they stick into prey, suck out blood.have pharynx they stick into prey, suck out blood. Secrete anticoagulants, vasodilators and numbing Secrete anticoagulants, vasodilators and numbing

agentsagents Marine segmented wormsMarine segmented worms

Wide variety of feeding modesWide variety of feeding modes

Phylum Mollusca:Phylum Mollusca:The “soft-bodied” The “soft-bodied”

animalsanimals

Evolutionary Evolutionary relationshipsrelationships

Protostomes, same Protostomes, same branch as annelids.branch as annelids.

Molluscan body plan (HAM)Molluscan body plan (HAM) ShellShell MantleMantle Visceral massVisceral mass Mantle cavityMantle cavity

With ctenidiaWith ctenidia

Head and assocated Head and assocated sensory structuressensory structures

RadulaRadula Foot and epipodial Foot and epipodial

tentaclestentacles

Molluscan body plan (HAM)Molluscan body plan (HAM) Digestive systemDigestive system

completecomplete note position of anusnote position of anus

Circulation/RespirationCirculation/Respiration ctenidiumctenidium open circulatory systemopen circulatory system coelom=pericardial cavity. coelom=pericardial cavity.

True coelom, but reduced.True coelom, but reduced.

Water/ion balance and Water/ion balance and ammonia excretionammonia excretion Has paired nephridia: Has paired nephridia:

kidney-like in functionkidney-like in function

Molluscan body plan (HAM)Molluscan body plan (HAM)

Nervous systemNervous system few ganglia at key locations, connected by few ganglia at key locations, connected by

paired ventral nerve cords.paired ventral nerve cords. have brainhave brain several sensory structures (see description several sensory structures (see description

of HAM)of HAM)

Major Molluscan ClassesMajor Molluscan Classes LEARN!: How is HAM modified for LEARN!: How is HAM modified for

each of the major classes?each of the major classes?

??

Class Polyplacophora: Class Polyplacophora: “many plates”“many plates”

The chitonsThe chitons Differences from HAMDifferences from HAM

8 shell plates8 shell plates Expanded mantle cav.Expanded mantle cav.

Multiple ctenidiaMultiple ctenidia

Mantle grows over shellMantle grows over shell Reduced headReduced head

Class Gastropoda: Class Gastropoda: “stomach-foot”“stomach-foot”

Representative members: Snails, Representative members: Snails, limpets, abalone, nudibranchs, sea limpets, abalone, nudibranchs, sea and land slugsand land slugs

Differences from HAMDifferences from HAM Undergo torsion (sketch)Undergo torsion (sketch)

What is torsionWhat is torsion Advantages of torsionAdvantages of torsion Disadvantages of torsionDisadvantages of torsion

Class Bivalvia:Class Bivalvia:“two valves”“two valves”

Representative members: Clams, Representative members: Clams, mussels and scallopsmussels and scallops

Differences from HAMDifferences from HAM Two shellsTwo shells Expanded mantle cavityExpanded mantle cavity Enlarged ctenidiaEnlarged ctenidia

Respiration AND feedingRespiration AND feeding

Reduced headReduced head Foot more elongateFoot more elongate

Class Cephalopoda:Class Cephalopoda:“Head-footed”“Head-footed”

Representative members: Nautilus, squid, octopusRepresentative members: Nautilus, squid, octopus Differences from HAMDifferences from HAM

Shell reduced (pen in squid)Shell reduced (pen in squid) Foot gives rise toFoot gives rise to

tentacles tentacles funnelfunnel

MantleMantle Thickened and protectiveThickened and protective Functions in movementFunctions in movement

Nervous system highly developedNervous system highly developed Great brain!Great brain! Eyes similar to vertebratesEyes similar to vertebrates

Circulatory system closed!Circulatory system closed! Other featuresOther features