Download Molluscs Ch. 11

Chapter 12
Molluscs
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Phylum Mollusca
– molluscus= “soft body”
octopus
• ~ 100,000 species
• diverse
• Size: < 1 cm  18 m
long
snail
slug
chiton
scallop
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cuttlefish
clam
Nautilus
Giant squid Architeuthis
Characteristics of Phylum Mollusca
• Wide variety of
habitats
– Tropics  polar seas
– Most are marine,
some freshwater,
some terrestrial
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Giant clam
Characteristics of Phylum Mollusca
• 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
(Endoderm)
bands (next slide)
(mesoderm)
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Fig. 9-13, p188
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Characteristics of Phylum Mollusca
• Unsegmented
– closest common ancestor shared with segmented worms
(Phylum Annelida) (ie. earthworms)
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Characteristics of Phylum Mollusca
• All organ systems are present, well-developed
– Respiratory organs
– Circulatory system, with heart
• Greater body size possible
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Squid
Freshwater clam
Molluscan body form
2-part body plan:
1. Head-foot
2. Visceral mass
Octopus
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Head-foot
Head:
– anterior
– Cephalic sensory organs
– Feeding organs:
Radula
Snail radula
– Most molluscs (not
bivalves)
– rasping structure
– Tongue-like
– Rows backwardpointing “teeth”
– Scraping food
– drilling
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• Mollusk Body Plan
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Head-foot
Foot:
• ventral
•
•
•
•
Muscular structure
Locomotion
Attachment
modifications
Octopus
http://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
molluscs
• 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
molluscs
– Closed circulatory system (Class Cephalopoda)=
• Blood confined to vessels
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• Video clip- aquatic snail (note heart)
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Molluscan reproduction
• Mostly dioecious
Giant squid
Long-finned squidLoligo
http://www.biology.ualberta.ca/courses.hp/zool250/Labs/Lab08/Lab08.htm19
Classes of Molluscs
• Class Polyplacophora
• Class Scaphopoda
• Class Gastropoda
• Class Bivalvia
• Class Cephalopoda
• Others…
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Classes of Mollusc
Class Polyplacophora
– “many plate-bearers”
– Chitons
– Dorsoventrally
flattened
– Shell= 8 overlapping
dorsal plates
– marine
Chiton
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Underside of chiton
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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Class Gastropoda
Gastro= gut
– Poda= foot
• Snails, limpets, slugs, whelks, cone
snails, conchs, periwinkles, abalone,
sea slugs….
Limpet
• Largest class
• Most diverse
• Marine, freshwater,
terrestrial
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Silver cloud nudibranch
Pulmonate snail
Class Gastropoda (cont’d)
• Microscopic  1m
long (sea hare)
– Typically 1-8cm
long
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Class Gastropoda (cont’d)
• Basically bilateral
– Visceral mass, mantle, mantle cavity undergoes
torsion (twisting) asymmetrical
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Class Gastropoda (cont’d)
– Moves mantle cavity, w. gills, anus, visceral
organs to anterior
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Class Gastropoda (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 (cont’d)
• May have protective shell
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Class Gastropoda
• Well-developed sense organs
– Eyes at base or at end of tentacles
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Gastropod feeding habits:
– Herbivores
– Carnivores
http://eebweb.arizona.edu/c
ollections/Fishes/Photograp
hs.htm
Red abalone
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Moon snail- uses radula to drill holes in bivalve (ie. clams)
Land snail
• Food for humans
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Cone snail
• Marine
• Venomous
• Contain analgesic
Video Eating fish
Nat Geo Cone snail
Cone snail
Barbed radula tooth containing
neurotoxin- powerful analgesic
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Abalone
• Several holes in top of shell
– Excrete waste
• Food for humans
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Slug
• No shell
• Garden pest
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Limpets
• Cling to rocks or other surfaces
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Conch
• Large shell
• Marine
• herbivores
Human impact
Feeding on ocean floor
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Class Bivalvia
• clams, oysters, mussels, scallops
• soft body between two halves of a hinged shell
Giant clam
California mussel
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Class Bivalvia (cont’d)
• Aquatic
– most marine,
some fresh
water
• no tentacles,
head, radula
• adductor muscle
• Large ciliacovered gills (in
most)
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Bivalve 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
bivalves
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
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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Locomotion
• 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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Oyster
• 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 Production
•
protective function
– foreign substance
between mantle & shell
• mantle secretes pearly
layers of nacre around
substance
Shell
Epithelium
Developing pearl
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Zebra mussel
• Environmental
Pest
• Ballast water
of ships from
Europe in
1986
Zebra mussel
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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)
• Live in high
densities
• Reproduce rapidly
Lake Michigan
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http://epod.usra.edu/archive/epodviewer.php3?oid=135264
Zebra Mussels (cont’d)
• Killed all native mussels in Lake Erie
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Distribution of Zebra Mussel
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Giant Clam & Burrowing Clam
• some= food
Siphon
Giant clam
Burrowing clam
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Scallops
• coarsely ribbed
• food
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Shipworms
• Destructive
• Burrow into wood
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Class Cephalopoda
• squid, octopus, nautilus, cuttlefish
ammonoids
• “head foot”
• Largest, most complex
invertebrates
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• most highly developed mollusc
– Most active and intelligent
• Marine predator
– carnivorous
Cuttlefish camouflage
Cuttlefish
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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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Octopus
• 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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Octopus
• camouflage
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http://www.cephbase.utmb.edu/viddb/vidsrch3.cfm?ID=132&CephID=495
• Some octopi can kill humans:
– Blue-ringed octopus
• Size of golf ball
• Bacteria in salivary glands
• Paralysis, but victim fully conscious
Blue-ringed octopus
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http://www.australiancephalopods.com/occy_blue_ring.html
Nautilus
• Up to 94 tentacles
– No suckers
• Shell with many gas
chambers
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Nautilus
Ammonoids
• Extinct
– 400 to 65 MYA
• Died out with
dinosaurs
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