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Today’s Objectives:
TSW list key characteristics of mollusks, including, but not limited to,– Major organs/organ systems– Major classes and representatives– Economic importance– Evolutionary history– Other major characteristics
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Mollusks
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New evolutionary steps
Protostomes, characters including– Trochophore larvae
– Spiral cleavage
– Schizocoelous coelom formationEucoelomateAdvanced brain (some classes)
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Key characteristics
Head-foot Visceral mass Mantle & mantle cavity True coelom only in cavities around
– Heart – Nephridia– Gonads
True circulatory system Radula often present
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Gastropoda – Gut Foots
Includes snails, limpets, & slugs Freshwater, marine, and terrestrial Display torsion Shell coiling Move on mucus with cilia or use foot
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Gastropod Feeding Methods
Use radula to scrape algae Some radula modified to pierce prey Protostyle in digestive cavity
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Gastropod Respiration & Circulation Gas exchange in mantle cavity Can have 1 or 2 gills Some have a siphon
Open circulatory system Blood acts as a hydraulic skeleton
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Gastropod Nervous System
Nerves concentrated into large ganglia Most ganglia in head Simple or complex eyes Statocysts Chemoreceptors
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Gastropod Excretory System
Nephridium (nephridia – plural) Ammonia is the primary waste product
in aquatic species Uric acid is the waste for terrestrial
species
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Gastropod Reproduction
Can be monecious or dioecious Usually cross-fertilize inside the mantle
cavity First development of a penis Marine gastropods produce a veliger
larva
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Economic Importance of Gastropods
Garden pestsGood eating – escargot
Major intermediate host for several nasty parasitic infections
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Representative Gastropods
Nudibranchs – sea slugs Helix pomatia – escargot Garden slugs
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Bivalvia – 2 Shells Umbo Hinge Nacre – mother of
pearl Shell made of
calcium carbonate
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Bivalve Respiration & Circulation Gills expanded into multi-layered sheets
(lamellae) Usually 2 siphons – incurrent &
excurrent
Open circulatory system
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Gastropod Feeding & Digestion
Labial palps filter food particles Mucus food string Crystalline style Gastric shield
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Bivalve Nervous System
Ganglia located in esophagus, foot, and adductor muscle
Most sense organs located in margin of mantle (some have eyes there too)
Statocysts Chemoreceptors
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Bivalve Reproduction
Most are dioecious, some monoecious Gonads in visceral mass Fertilization usually external
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Bivalve Development
Trochophore larva Veliger larva Glochidium – often parasitic
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Bivalve Economic Importance
Often used as food Pearl production Invasive species – zebra mussel
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Representative Bivalves
Mytilus – common mussel Pinctada – pearl oysters Dreissena polymorpha – zebra mussel
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Cephalopoda – Head Foots
Octopi, squid, nautili, cuttlefish Tentacles Jet Propulsion Closed Circulatory System
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Cephalopoda Shell
External on nautili Internal in squid (pen) Internal in cuttlefish (cuttlebone) Absent in octopi
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Cephalopoda Locomotion
Use siphon for jet propulsion Squeeze mantle cavity forcefully Sometimes have external “wings” or fins
for steering or slow locomotion Nautili use internal air for neutral
buoyancy
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Cephalopoda Feeding
Most capture prey by sight– Use arms or tentacles to grab (sometimes
have hooks and suckers)– Bring prey to beaked mouth
Muscular digestive system Digestion in stomach and cecum Anus near the funnel
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Cephalopoda Respiration & Circulatory Systems Closed ciculatory system – more
efficient 3 hearts High metabolic rates
Respiration through gills
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Cephalopoda Nervous System Complex brains Very advanced, large eyes Statocysts Touch receptors Chemoreceptors Chromatophores – color changing,
signalling Some bioluminescent Ink gland
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Cephalopoda Reproduction & Development
All are dioecious Males have testes and package sperm
in spermatophores Fertilization mostly internal in back of
female’s mantle cavity– Octopi have external fertilization of eggs
Often males have hectocotylus All larval development inside eggs.
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Economic Importance of Cephalopods Research on nervous system Bait Food – calamari Minerals for pets – cuttlebone
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Representative Cephalopods
Loligo – common squid Architeuthis dux – giant squid Octopus dofleini – Giant pacific octopus
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The Vampire Squid from Hell!!!!
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Polyplacophora – Many Plate Bearing Animals Used for food – hard to chew Chitons Crawl over floor using muscular foot Can roll into a ball for protection Most feed on algae Ladderlike nervous system
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Chiton
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Scaphopoda – Boat feet
Often called “tusk shells”
Burrowing animals
Conical shell open at both ends
Often feed on foraminiferans
Dioecious
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Monoplacophora – One Plate Bearing Animals Dioecious Considered
living fossils Neopilina Live in deep
ocean
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Caudofoveata – Animals with Tails in Small Pits Wormlike Deep sea floor dwellers Spicules on body wall
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Aplacophora – No Plate Bearers
Also called solenogasters
Lack a shell Nervous system
similar to flatworms
Live on corals Carnivores