Tree of Life

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Tree of Life
The tree of life according to Ernst Haeckel, 1891
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How does Porifera fit in?
Porifera
3 body types
Other animals
choanocytes
cellular level of organization
Blastula stage
heterotrophic
multicellular
eukaryote
unknown common ancestor
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How does Cnidaria fit in?
Cnidaria
Porifera
Other animals
3 body types
choanocytes
cellular level of organization
Blastula stage
heterotrophic
multicellular
unknown common ancestor
eukaryote
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Phylum Cnidaria
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Level of Organization
Tissue

• cells are organized into tissues and work
  together to accomplish physiological functions

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Tissue Layers

• Diploblastic 2 germ layers
• endoderm ? gastrodermis
• ectoderm ? epidermis
• mesoglea
• gelatinous matrix between the 2 layers

gastrovascular cavity
epidermis
mesoglea
gastrodermis
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General Body Plan

• sac-like body (only 1 opening)
• Food and waste go in/out the same opening
• ? no anus!
• water within GVC acts as a hydrostatic skeleton

mouth
oral surface
gastrodermis
Gastrovascular cavity
mesoglea
epidermis
aboral surface
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General Body Forms
2 different body forms are usually present in the
life cycle polyp
medusa
one animal may pass through both forms during
its life
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General Life Cycle
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Radial Symmetry

• - body parts are arranged concentrically around
  an oral-aboral axis

oral
aboral
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Nematocysts

• specialized stinging organelles
• found within cnidocytes (cells)
• cnidocytes are located in epidermis

A cnidocyte with a nematocyst within it
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Nematocysts

• nematocysts are like mini-harpoons
• cnidocil senses movement acts like a trigger
• can inject poison, coil around prey, or be
  adhesive
• functions
• - prey capture defense

nematocyst
cnidocil
cnidocyte
Undischarged
Discharged
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Colony formation

• colony formation is common (colonial animals)
• occurs via asexual reproduction (e.g. fission)
• individual polyps are connected to one another
  by the GVC

individual polyp
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Physiology

• Feeding
• nematocysts within cnidocytes
• tentacles
• Digestion
• extracellular (in GVC)
• intracellular (by gastrodermal cells)
• incomplete system (no anus)
• Gas exchange Excretion
• these systems are absent

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Physiology

• Nervous System
• nerve net
• (no central nervous system no brain)
• sense organs
• statocysts (equilibrium organs)
• ocelli (photosensitive organs)
• Skeletal System
• water in GVC acts as a hydrostatic skeleton

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Physiology

• Reproduction
• Asexual
• budding
• longitudinal fission
• pedal laceration
• (e.g. sea anemones)

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Physiology

• Reproduction
• Sexual
• usually dioecious
• (separate sexes? e.g. humans)
• monoecious
• (both male female gonads in 1 individual)
• results in Planula larva

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Phylum Cnidaria

• Class Hydrozoa
• Class Scyphozoa
• Class Anthozoa

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Class Hydrozoa

• medusa polyp body forms

Fire coral
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Class Hydrozoa

• medusa polyp body forms
• most are colonial
• ? colonies are formed of individual zooids

a single zooid
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Class Hydrozoa

• many of these colonies show polymorphism
• ? this is where there are several different types
  of polyps/zooid and each type is specialized for
  a different function
• e.g. gastrozooids feeding polyps
• e.g. dactylzooids defense polyps
• ? all the zooids within a colony are genetically
  identical
• ? these different zooids work together in the
  colony

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Class Hydrozoa
- a sessile colony showing polymorphism
gonozooid
entire colony
gastrozooid
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Class Hydrozoa
- a Portugese Man-o-war is a floating hydrozoan
colony showing polymorphism
pneumatophore
entire colony
gastrozooid
dactylzooid
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Class Hydrozoa- life cycle
sexual reproduction
asexual reproduction
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Class Hydrozoa

• Hydra is an example of a solitary, freshwater
  hydrozoan

asexual reproduction
sexual reproduction
gonads
bud
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Class Scyphozoa

• true jellyfish
• medusa polyp body forms
• thick mesoglea

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Class Scyphozoa- life cycle
sperm
egg
ephyra
Adult medusa
strobila
scyphistoma
larva
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Class Anthozoa

• polyp body form ONLY
• all marine

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Class Anthozoa

• some are colonial
• ? colonies are formed of individual zooids

• some are solitary

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Class Anthozoa
Sea anemones
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Class Anthozoa
Soft Corals
Sea pen
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Class Anthozoa
Stony Corals
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Class Anthozoa- life cycle
Sexual reproduction
sperm
egg
larva
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Class Anthozoa- life cycle
asexual reproduction
fission
pedal laceration
fission
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How does Cnidaria fit in?
Cnidaria
3 classesHydrozoa, Scyphozoa, Anthozoa
Porifera
2 body types polyp, medusa
diploblastic
3 body types
tissue level of organization
choanocytes
cellular level of organization
Blastula stage
heterotrophic
multicellular
unknown common ancestor
eukaryote
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Symbiosis

• Mutualism
• Corals contain endosymbiotic algae called
  zooxanthellae
• the zooxanthellae photosynthesize and provide
  food for the coral while the coral provides a
  safe home

zooxanthellae
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Symbiosis

• Mutualism
• Many species of anemone fish (clown fish) live
  within anemones and are immune to their stinging
  nematocysts
• the fish may lure in other fish for the anemone
  to capture and eat, while the anemone provides
  protection and a home

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Coral Reefs

• What are they?
• stony corals lay down a calcium carbonate
  skeleton
• these skeletons are laid down on top of one
  another and over thousands of years, form large
  calcium carbonate structures
• these large structures, along with the plants
  and animals that inhabit them, are known as
  coral reefs
• Where do they form?
• in optimal conditions for their zooxanthellae
• ? shallow, warm, nutrient-poor waters

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Importance of Coral Reefs

• one of the most productive ecosystems although
  the water is nutrient-poor
• hot spots for biodiversity

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Threats to Coral Reefs

• over-enrichment of nutrients from sewage and
  agricultural run-off
• overfishing of herbivorous fish
• global warming (leads to coral bleaching where
  corals expel their zooxanthellae)