What’s in a Name? - MS. AU'S WEBSITE · 3) • Also affected by ocean acidification Key derived...
Transcript of What’s in a Name? - MS. AU'S WEBSITE · 3) • Also affected by ocean acidification Key derived...
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What’s in a Name?Class Name Meaning (Latin/Greek)
Aplacophora No shell
Monoplacophora One shell
Polyplacophora Many shells
Scaphopoda Tusk shell
Bivalvia Two valves
Gastropoda Stomach-foot
Cephalopoda Head-foot
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Phylum MolluscaN A U T I L U S , S Q U I D , O C T O P U S E S , S N A I L S , S L U G S , S C A L L O P S , C L A M S , O Y S T E R S , M U S S E L S , N U D I B R A N C H S
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Mollusca: overview❖ Enormous biodiversity (see intro slides)• 90% are snails or bivalves
• Cephalopods the most intelligent invertebrates
❖ Over 95,000 species: all habitats, but mostly aquatic
❖ Good fossil record: many secrete shells
❖ Related to segmented worms
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Mollusca: major characteristics• (Three germ layers: endoderm, mesoderm, ectoderm)
• Bilateral symmetry or asymmetrical
• Mantle (organs within cavity; can secrete shell)
• Muscular ventral foot: adapted for various functions
• Digestive system: complete gut, torsion, radula
• Circulatory system: mostly open (closed for cephalopods)
• Respiratory system: gills
• Skeleton: hydrostatic, exoskeleton, endoskeleton
• Nervous system: very simple → very complex
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Basic Body Plan❖ Head
❖Mantle, mantle cavity
❖ Shell
❖ Visceral mass (internal organs)
❖Muscular foot
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Basic Body Plan
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Basic Body Plan
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Basic Body Plan
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Basic Body PlanMantle
❖ Layer of epidermis
❖ Contains sense organs, glands, including:• Shell gland (produces shell)• Mucous gland
Mantle cavity
❖ Region covered/protected by mantle
❖Waste and gametes empty into mantle cavity before release
❖ Some molluscs retract head or foot into mantle cavity
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Basic Body PlanShell
❖ Secreted by mantle
❖Made of calcium carbonate (CaCO3)• Also affected by ocean acidification
❖ Key derived trait, used to distinguish between molluscan taxa
❖ Adapted for many purposes*
*See “Skeleton” slides
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Skeleton
Review!
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SkeletonShell adapted for many structural/protective purposes:
❖ Gastropods and bivalves: outer shell for protection (exoskeleton)
❖ Squid: reduced endoskeleton, for structural support only (“pen”)
❖ No shell in octopus• Relies on hydrostatic skeleton only
• Flexible body
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Skeleton
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Basic Body PlanVisceral Mass
❖ Contains most of the body organs (reproductive, excretory, circulatory, etc)
❖ In most molluscs, protected by shell
Foot
❖ Varies greatly in shape/function
❖ Generally used for locomotion, to anchor animal to surfaces
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Germ Layers❖ 3 germ layers: endoderm, mesoderm, ectoderm
❖ Origin of some structures:• Mantle – ectoderm
• Gills – mesoderm
❖Most structures ambiguous (don’t memorize):• Muscular Foot – mesoderm, ectoderm
• Visceral mass a combination of different layers
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Molluscs have bilateral symmetry or asymmetry
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Digestive System❖ Complete gut
(separate mouth and anus)
❖ Torsion in gastropods
❖ Radula adapted for many functions
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The Tale of Two Gastropods
Garden Snail (torted)
Nudibranch (detorted)
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The Tale of Two Gastropods
Garden Snail (torted)
Nudibranch (detorted)
Why does the garden snail “poop on its head”?
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Thought Experiment
Would you rather?
• Have no head OR
• Lose your hypothetical tail
What body part do you protect first in an earthquake?
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Torsion
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Torsion (gastropods only)❖ During development, mantle cavity faces posteriorly• Tuck in tail before head
❖ Torsion: twist entire mantle/mantle cavity/shell to face anteriorly• Tuck in head before tail…better protection!
• Unfortunate side effect: a snail’s anus empties near its head and gills
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Digestive System: Radula❖ Unique to molluscs
❖ Tonguelike rasping organ in mouth, a “conveyor belt of teeth”
❖ Scrapes/cuts food before enters esophagus
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Digestive System: Radula
m = mouthe = esophagus
r = radulamu (rr/op/rp) = muscle
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Digestive System: Radula❖ Unique to molluscs
❖ Tonguelike rasping organ in mouth, a “conveyor belt of teeth”
❖ Scrapes/cuts food before enters esophagus
❖ Adaptations:• Scrape algae off of rock (e.g. snails)
• Poisoned harpoon teeth (e.g. predatory marine snails)
• Cutting prey (e.g. squid, octopus)
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Digestive System: Radula
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Digestive System: Radula
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Life Cycle & Reproduction❖Most molluscs have male and female forms
❖Mostly sexual reproduction
❖ Zygote → Larvae (trochophore) → Adult
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Why are annelids and molluscs similar?S H A R E D D E V E LO P ME N TA L STAG E : T R O CO PHOR E L A RVA E
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Respiratory System❖ Terrestrial molluscs have primitive lungs (absorb oxygen
directly from air)
❖ Aquatic molluscs have gills called ctenidia: absorb oxygen from water, transfer to bloodstream
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Respiratory System❖ Terrestrial molluscs have primitive lungs (absorb oxygen
directly from air)
❖ Aquatic molluscs have gills called ctenidia: absorb oxygen from water, transfer to bloodstream
❖ Nudibranch (“nudi-” = naked; “branch-” = gills)
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Complete Circulatory System
❖Circulatory system: • Transports nutrients (e.g. oxygen, sugar) to all body cells
• Transports wastes (e.g. carbon dioxide, nitrogen) away from cells
❖Sponges, cnidarians, flatworms:• No circulatory system
• All cells in direct contact with water: oxygen diffuses in and wastes diffuse out
Review!
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❖Open circulatory system:• Tissues ‘bathed’ in blood
• Heart pumps blood between body compartments
• Nutrients/wastes diffuse directly between blood cells and body cells
❖Closed circulatory system:• Heart(s) pumps blood through vessels
• Blood contained within vessels
• Nutrients/wastes diffuse between blood cells and body cells through vessel wall
Review!
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Circulatory System❖ Open circulation in most molluscs
❖ Closed in cephalopods (open circulation too slow; not enough for fast-moving, intelligent cephalopods)
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Nervous system❖ Ladder-like nervous system (like annelids)
❖ Ring of ganglia in head area
❖ Sensory organs:• Locations and appearance vary widely
• Have eyes, sense of smell/taste, etc.
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Class Bivalvia❖ Clams, oysters, mussels, scallops, etc
❖ Have two shells (bi = “two”; valve = “shell”)
❖ Filter feeders
❖ Pump water in one direction over gills and mucous string (where food particles are trapped)
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Class Bivalvia
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Class Gastropoda❖ Snails, slugs, nudibranchs
❖ “Stomach-foot”: • Foot located ventrally
• Foot used for locomotion
❖ Torsion
❖ Secrete slime trails (using mucous gland) to aid with locomotion• Not testable: hormones left in slime trails help attract mates!
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Class Cephalopoda❖ Squid, nautilus, octopus
❖ “Head-foot”
❖ Closed circulatory system
❖ Highly developed nervous system:• Large image-forming eyes
• 1 central brain + 8 ganglia (one per arm!)
• Most intelligent of invertebrates
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Class CephalopodaCephalopods’ brain to body mass ratio is comparable to vertebrates
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Class CephalopodaCephalopods’ brain to body mass ratio is comparable to vertebrates
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Class Cephalopoda❖ Squid, nautilus, octopus
❖ “Head-foot”
❖ Closed circulatory system
❖ Highly developed nervous system:• Large image-forming eyes
• 1 central brain + 8 ganglia (one per arm!)
• Most intelligent of invertebrates
❖ Chromatophores: specialized cells capable of colourchange for camouflage
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Class Cephalopoda: Chromatophores
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Eye Evolution❖ Evolution of Human Eye Video
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Activity❖ Compare and contrast Phylum Annelida and Phylum
Mollusca. • (There are at least 9 similarities…how many can you come up with?)
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Mollusc evolutionSelective pressures:
1. Competition among seafloor-dwellers
2. Competition for food
3. Defense against predators
Adaptations:
→ Floating (1)
→ Specialization of radula (2)
→ Specialization/adaptation of shell shape (3)
→ Camouflage (cephalopods) (3)
→ Toxicity (nudibranchs) (3)
→ Intelligence (2, 3)
→ Foot structure, function (1, 2, 3)
Note: based off of “Molluscs Survival Game” video
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Vocabulary List❖ Mollusca
❖ Gastropod, Cephalopod, Bivalve
❖ Nudibranch, nautilus, squid, octopus, snail, slug, clam, mussel, etc.
❖ Mantle, Mantle cavity, Shell, Visceral mass, Foot
❖ Shell gland, Mucous gland
❖ Endoskeleton, Exoskeleton, Hydrostatic skeleton
❖ Ectoderm, Mesoderm, Endoderm
❖ Bilateral Symmetry, Asymmetry
❖ Torsion
❖ Radula
❖ Trochophore
❖ Ctenidia
❖ Open circulatory system, closed circulatory system
❖ Ganglion
❖ Ladder-like nervous system
❖ Chromatophore
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Further reading: molluscs❖ https://www.ck12.org/biology/mollusk-structure-and-
function/lesson/Mollusk-Structure-and-Function-Advanced-BIO-ADV/