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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Today! 1. Different +ssues allow specializa+on in diploblasts
1. Describe how Ectoderm/Endoderm share the work requiredfor an organisms to grow
2. Describe how cnidarians sense and respond to the outsideworld
3. List the factors that allow cnidocytes to re2. Explore the diversity of Cnidaria
1. Contrast between the four major types of cnidarians2. Explain how a variety of cnidarians replicate3. Iden+fy the special adapta+ons of coral building cnidaria
3. Introduce the Ctenophora1. Contrast between Cnidaria and Ctenophora
Lecture 4: Cnidaria and Ctenophoraà diploblasts have more fun!
Lo o k f o r m o r e l e a r ni ng o b j e c t i v e s s o o n!
7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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The Diploblasts
Two germ layers, differing in function:• ECTODERM- sensation, protection, food capture
- Excretion, Support, Movement, (Reproduction)
• ENDODERM- Food Processing
• Include Cnidaria, Ctenophoresà Radial and biradial symmetry
• Mesoglea• In Cnidaria & Ctenophores• Middle “jelly” layer • Support, Elastic skeleton• Mostly water, collagen Fig 13.3
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Cnidarian cell types
Epitheliomuscular cells
Cnidocyte
Sensory Cells
Gland cells
Myofibrils
Nutritive-muscular cells
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Cnidarians• Over 9,000 species • OLD!
– Fossil specimens dated to over 700 million years ago
Cnidocytes contain nematocysts
Fig 13.4
Cnidocytes are “one-time use” cells• Chemosensory Supporting cells – organic molecules from prey• Cnidocil – “trigger”, modified cilium sensitive to touch
Only Cnidarians
make cnidocytes
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Cnidocytes contain nematocysts N o t a l l
^
Three main types:1. Nematocysts – inject toxin for prey capture / defense
– found in all classes of Cnidaria
2.
Spirocysts – adhesive, found only in the anthozoa3. Ptychocysts – used by Ceriantaria (class of anthozoa ) toanchor their bodies in soft substrate ( i.e. sand )
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Firing nematocysts
After the proper stimuli … Two forces contribute to firings1. Tension
- structural, develop duringformation
2. Osmotic Pressure- Large concentration gradient in
the cnidocyte- Opening operculum cause water
to rush in- é water volume causes
nematocyte to shoot out
Fig 13.5
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Cnidaria are dimorphic à two morpho types
Fig 13.3
Epitheliomuscular cells as most of
epidermisà extends parallel to tentaclesà Contain contractile fibrils
Gastrovascular cavity“blind gut ”à medusa have manubrium
Nerve Netà diffuse nervous systemà part of neuromuscular systemà Rhopalia sense organs in some
medusa
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Fig 13.2
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Hydrozoa• Most marine and colonial
•
Both polyp and medusa forms• Colonial Obelia have a more typical life cycle of hydrozoa• Hydra have an atypical life cycle
Hypostome
MouthTentacle
Basal Disc
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Hydrozoa• Hydra have an atypical life cycle
Asexual à
Sexual
1. Bud appears2. Grows3. Detaches
• Most species are dioecious• Fall
Ø lower temperatures cause temporary gonads togrow
Ø Testes (top) and Ovaries (bottom) appear asrounded projections
Ø Sperm are released and fertilize attached ovaryØ Development to cysts form, breaks loose
à can survive the winter • Spring
Ø Warmer water prompts hatching
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Fig 13.7
• Colonial Obelia have a more typical life cycle of hydrozoa
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Scyphozoa – “true jellyfish”• many of the largest jellyfish• float in open sea
• One order sessile, attached to seaweeds
Fig 13.19
Life cycleof Aurelia
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Cubozoa• Medusa form is dominant• Polyp is very tiny / unknown• Umbrella is square
• 1+ tentacles at each corner • Strong swimmers• Feed on fish in nearshore areas• The sea wasp ( Chironex fleckeri )
• Potentially fatal sting• Death within a matter of
minutesFig 13.21
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Fig 13.21
Anthozoa – “flower animals”• Polyps dominate the life cycle
– No medusa• For replication à planula larvae• Gastrovascular cavity divided by
septa / mesenteries – Hold the gonads, when produced
• 3 subclasses à Hexacorallia – 6-fold symmetry – Sea anemones – Stony corals
– Zoanthids
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Fig 13.21
Anthozoa – “flower animals”
Sea Anemones(you will see one in the lab)• Larger and colourful• Attach with pedal disc
– can glide along a surface
• Ciliated oral disc & pharynx – creates water current (O 2, waste) – hydrostatic skeleton
•
Symbiotic zooxanthellae – photosynthetic algae – provide nutrients for anthozoa – algae has a safe place to live
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7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Fig 13.28
Anthozoa
Hexacorallian (Stony) Coral• Similar to anemones• Produce calcereous exoskeleton
– Produced by epidermis at base of animal
– Create ridges, sclerosepta , that allowretraction
– In colonies, sheet of tissue covers thecolony, connecting gastrovascular cavities of all polyps
✔ Divided gut
✔ Tentacles✗ Ciliated mouth✗ Pedal Disc
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Fig 13.28
Anthozoa
Hexacorallian (Stony) Coral• Similar to anemones• Produce calcereous exoskeleton
– Build-up of this material leads to coralreef formation
• Symbiotic zooanthellae in thehermatypic corals – Not in ahermatypic corals
only in
7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Coral Reefs• Diversity of organisms rivaled only by tropical rainforests• Hermatypic corals and coralline algae form most
coral reefs worldwideà Precipitation of CaCO 3 helps hold the reef together
– Require warmth, light, and salinity of undiluted seawater
– Limited to shallow waters between 30 degrees northand 30 degrees south latitude
– Photosynthetic zooxanthellae live in their tissues
7/29/2019 Biol 110 - Lecture 6 Notes - Sept 26, 2013
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Coral Reefs – Photosynthetic zooxanthellae live in their tissues
Share products ofphotosynthesiswith coral
Recycle wasteNitrogen andPhosphours
for coral
Enhance theprecipita+onof CaCO3
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Coral Reefs – Photosynthetic zooxanthellae live in their tissues
Share products ofphotosynthesiswith coral
Recycle waste Nitrogenand Phosphours for coral
Enhance theprecipita+on ofCaCO3
“Coral Bleaching”increasing ocean temperaturesresulting from global climatechange, damages zooxanthellaephotosynthetic machinery, releasingtoxic oxidants to the coral
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Out to sea
R
e e
f T y p e s
Fig 13.36
1.
2.
3.
4.
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• About 150 species • Eight rows of comblike plates of cilia used for
movement – A few creeping, sessile but mostly
swimming à weak swimmers
• Biradial symmetry due to two tentacles• Oral-aboral axis, no head
Cnidaria
• Ctenophore phylogeny is still quite disputed
• We will not consider the different taxa of Ctenophores
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Cnidaria.vs.
Ctenophores
✔ Diploblasts✔ Middle “jelly” layer
à contains muscle fibers in ctenophores✔ Diffuse Nerve Net
✗ Ctenophores no found in freshwater ✗ Complete gut in Ctenophores✗ Colloblasts ( sticky ) not choanocytes ( stingy )✗ Ctenophores mostly monoecious
à Cnidaria may be mono- or dio-
Fig 13.38