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
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