Chapter 12 Molluscs

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Chapter 12Chapter 12MolluscsMolluscs

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Phylum MolluscaPhylum Mollusca– molluscus= “soft body”

• ~ 100,000 species

• diverse

• Size: < 1 cm 18 m long

cuttlefish Nautilus Giant squid Architeuthisclam

chiton

snail

slug

octopus

scallop

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Characteristics of Phylum Characteristics of Phylum MolluscaMollusca

• Wide variety of habitats– Tropics polar

seas

– Most are marine, some freshwater, some terrestrial

Giant clam

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Characteristics of Phylum Characteristics of Phylum MolluscaMollusca

(Endoderm)

(mesoderm)

• Eucoelomates

– True coelom, lined with mesodermal peritoneum (membrane that lines coelom, covers coelomic viscera)

•mesentery- mesodermal sheet that suspends internal organs in coelom

– Schizocoelous

•Coelom forms by splitting of mesodermal bands (next slide)

5Fig. 9-13, p188

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Characteristics of Phylum Characteristics of Phylum MolluscaMollusca

• Unsegmented– closest common ancestor shared with segmented

worms (Phylum Annelida) (ie. earthworms)

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Characteristics of Phylum Characteristics of Phylum MolluscaMollusca

• All organ systems are present, well-developed– Respiratory organs

– Circulatory system, with heart

• Greater body size possible

Freshwater clamSquid

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MolluscanMolluscan body form body form

2-part body plan:1. Head-foot

2. Visceral mass

Octopus

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Head-footHead-foot

Snail radula

Head:– anterior– Cephalic sensory

organs– Feeding organs:

Radula

– Most molluscs (not bivalves)

– rasping structure

– Tongue-like

– Rows backward-pointing “teeth”

– Scraping food

– drilling

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• Mollusk Body Plan

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Head-footFoot:

•ventral

•Muscular structure

•Locomotion

•Attachment

•modifications

Octopushttp://acolyte.org/images/octopus.png

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Visceral mass•Digestive organs

•Reproductive organs

•Circulatory organs

•Respiratory organs

Mantle

•Attached to visceral mass

•Dorsal skin folds

•protective

• In some, mantle secretes protective shell over visceral mass

Chiton

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Mantle cavity– Space between

mantle and foot

– Opens to outside

– Functions:

•Gas exchange (respiration)

•Excretion/elimination

•Release reproductive products

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Circulatory system of Circulatory system of molluscsmolluscs

• Open circulatory system (except Class Cephalopoda)– Open circulatory system

•heart pumps hemolymph (blood) through body cavity, b/w cells

•No small blood vessels

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Circulatory system of Circulatory system of molluscsmolluscs

– Closed circulatory system (Class Cephalopoda)=

•Blood confined to vessels

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• Video clip- aquatic snail (note heart)

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Molluscan reproductionMolluscan reproduction

• Mostly dioecious

http://www.biology.ualberta.ca/courses.hp/zool250/Labs/Lab08/Lab08.htm

Long-finned squid- Loligo

Giant squid

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Classes of MolluscsClasses of Molluscs

• Class Polyplacophora

• Class Scaphopoda

• Class Gastropoda

• Class Bivalvia

• Class Cephalopoda

• Others…

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Classes of MolluscClasses of Mollusc

Chiton

Class Polyplacophora– “many plate-

bearers”

– Chitons

– Dorsoventrally flattened

– Shell= 8 overlapping dorsal plates

– marineUnderside of chiton

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Class Scaphopoda– Tooth shells

– Long, slender body

– Burrows into mud

– Shell open at both ends

http://www.ucmp.berkeley.edu/mollusca/scaphs/scaphopoda.html

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Silver cloud nudibranch Pulmonate snail

Limpet

Class GastropodaClass GastropodaGastro= gut

– Poda= foot

• Snails, limpets, slugs, whelks, cone snails, conchs, periwinkles, abalone, sea slugs….

• Largest class

• Most diverse

• Marine, freshwater, terrestrial

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Class Gastropoda Class Gastropoda (cont’d)(cont’d)

• Microscopic 1m long (sea hare)– Typically 1-8cm

long

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Class Gastropoda Class Gastropoda (cont’d)(cont’d)

• Basically bilateral– Visceral mass, mantle, mantle cavity

undergoes torsion (twisting) asymmetrical

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Class Gastropoda Class Gastropoda (cont’d)(cont’d)

– Moves mantle cavity, w. gills, anus, visceral

organs to anterior

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Class Gastropoda Class Gastropoda (cont’d)(cont’d)

Why torsion?– Head withdraws into shell first

– Clean, undisturbed H2O enters mantle cavity

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Coiling– Absent in some

– Visceral mass/mantle may be coiled

– Successive coils- whorls

– Caused pressure on right side adaptation: loss of rt. kidney, auricle, gill

•Water enters via left, leaves right

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Class Gastropoda Class Gastropoda (cont’d)(cont’d)

• May have protective shell

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Class GastropodaClass Gastropoda

• Well-developed sense organs– Eyes at base or at end of tentacles

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Gastropod feeding habits:– Herbivores

– Carnivores

Moon snail- uses radula to drill holes in bivalve (ie. clams)

http://eebweb.arizona.edu/collections/Fishes/Photographs.htm

Red abalone

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Land snailLand snail

• Food for humans

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Cone snailCone snail

• Marine

• Venomous

• Contain analgesic

Cone snailBarbed radula tooth containing neurotoxin- powerful analgesic

Video Eating fish

Nat Geo Cone snail

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AbaloneAbalone

• Several holes in top of shell– Excrete waste

• Food for humans

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SlugSlug

• No shell

• Garden pest

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LimpetsLimpets

• Cling to rocks or other surfaces

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ConchConch

• Large shell

• Marine

• herbivores

Human impact

Feeding on ocean floor

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Class BivalviaClass Bivalvia

• clams, oysters, mussels, scallops

• soft body between two halves of a hinged shell

California musselGiant clam

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Class Bivalvia (cont’d)Class Bivalvia (cont’d)

• Aquatic– most marine,

some fresh water

• no tentacles, head, radula

• adductor muscle

• Large cilia-covered gills (in most)

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Bivalve shell morphologyBivalve shell morphology

Umbo- oldest part of shell

– Growth in concentric lines around it

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• Valves open by adductor muscle– contraction= closed

– relaxing= open

• Hinge= mantle secretion of more protein, less calcium carbonate

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Water movement through Water movement through bivalvesbivalves

1. incurrent siphon - water into the mantle cavity

2. water circulates over the gills– Gas exchange

– Filter feeding

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Water movement through Water movement through bivalves (cont’d)bivalves (cont’d)

3. water flows past anus where waste is excreted

4. excurrent siphon – water out of the mantle cavity

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LocomotionLocomotion• Mostly sedentary/sessile

• highly developed muscular foot– often to burrow into sediment

– move by slicing-like motion of foot

– swim by chattering motion of shell (scallops)

•Clams not just for chowder movie

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OysterOyster

• lower valve is cemented to any object available

• Improve water quality

• Decrease bank erosion

• food

http://www.csc.noaa.gov/scoysters/images/bio/oysters2.jpg

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Pearl ProductionPearl Production

Developing Developing pearlpearlDeveloping Developing pearlpearl

EpitheliumEpitheliumEpitheliumEpithelium

ShellShellShellShell

• protective function

– foreign substance between mantle & shell

• mantle secretes pearly layers of nacre around substance

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Zebra musselZebra mussel

Zebra mussel

• Environmental Pest

• Ballast water of ships from Europe in 1986

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Zebra Mussels (cont’d)Zebra Mussels (cont’d)

• attach to any hard substrate– Other mussels,

clams, crayfish water pipes, docks, boats

• Outcompete other bivalves

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Zebra Mussels (cont’d)Zebra Mussels (cont’d)

• Live in high densities

• Reproduce rapidly

http://epod.usra.edu/archive/epodviewer.php3?oid=135264

Lake Michigan

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Zebra Mussels (cont’d)Zebra Mussels (cont’d)

• Killed all native mussels in Lake Erie

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Distribution of Zebra Distribution of Zebra MusselMussel

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Giant Clam & Burrowing Giant Clam & Burrowing ClamClam

• some= food

Giant clam

Siphon

Burrowing clam

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ScallopsScallops

• coarsely ribbed

• food

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• Destructive

• Burrow into wood

ShipwormsShipworms

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Class CephalopodaClass Cephalopoda• squid, octopus, nautilus,

cuttlefishammonoids

• “head foot”

• Largest, most complex invertebrates

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• most highly developed mollusc– Most active and intelligent

• Marine predator– carnivorous

Cuttlefish

Cuttlefish camouflage

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• shell reduced/absent & internalized (vestigal) (squid, octopus)

• Nautilus- shell

• Cuttlefish- small, enclosed by mantle

Octopus

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• head is well developed - large eyes – Complex eyes (except Nautilus)

•Cornea, lens, chambers, retina, iris

• Well-developed nervous system - complex brain

Squid

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• foot is modified into multiple tentacles with suckers (in some)– Grasp prey

– Taste via suckers

– crawling

– Movie MBA

• siphon forces out water: “jet propulsion”

• Octopus movement movie, octopus movement, MBA MBA

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• squid & octopus possess ink gland which produce melanin ; escape

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OctopusOctopus

• Eight arms with suckers

• Crawl or eject water from siphon

• Change skin color

• Most intelligent invertebrate– Colorblind, but can be taught different

shapes

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OctopusOctopus

• camouflage

http://www.cephbase.utmb.edu/viddb/vidsrch3.cfm?ID=132&CephID=495

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• Some octopi can kill humans: – Blue-ringed octopus

•Size of golf ball

•Bacteria in salivary glands

•Paralysis, but victim fully conscious

http://www.australiancephalopods.com/occy_blue_ring.html

Blue-ringed octopus

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NautilusNautilus• Up to 94

tentacles– No suckers

• Shell with many gas chambers

Nautilus

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AmmonoidsAmmonoids

• Extinct– 400 to 65 MYA

• Died out with dinosaurs