biol 110 - lecture 6 notes - sept 26, 2013

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!



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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Cnidarian cell types

Epitheliomuscular cells

Cnidocyte

Sensory Cells

Gland cells

Myofibrils

Nutritive-muscular cells




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




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 )




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




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




Fig 13.2




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




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




Fig 13.7

• Colonial Obelia have a more typical life cycle of hydrozoa




Scyphozoa – “true jellyfish”• many of the largest jellyfish• float in open sea

• One order sessile, attached to seaweeds

Fig 13.19

Life cycleof Aurelia




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




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




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




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




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



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



Coral Reefs – Photosynthetic zooxanthellae live in their tissues

Share products ofphotosynthesiswith coral

Recycle wasteNitrogen andPhosphours

for coral

Enhance theprecipita+onof CaCO3



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



Out to sea

R

e e

f T y p e s

Fig 13.36

1.

2.

3.

4.



• 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



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

biol 110 - lecture 6 notes - sept 26, 2013

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