Tree of Life
The tree of life according to
Ernst Haeckel, 1891
How does Porifera fit in?
Porifera
3 body types
choanocytes
cellular level
of organization
unknown
common ancestor
Blastula stage
heterotrophic
multicellular
eukaryote
Other animals
How does Cnidaria fit in?
Cnidaria
Porifera
Other animals
3 body types
choanocytes
cellular level
of organization
Blastula stage
heterotrophic
multicellular
eukaryote
unknown
common ancestor
Phylum Cnidaria
Level of Organization
Tissue
• cells are organized into tissues and
work together to accomplish
physiological functions
Tissue Layers
Diploblastic = 2 germ layers
• endoderm  gastrodermis
• ectoderm  epidermis
mesoglea
• gelatinous matrix between the 2 layers
epidermis
gastrovascular
cavity
mesoglea
gastrodermis
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
oral surface
gastrodermis
mesoglea
epidermis
aboral surface
mouth
Gastrovascular
cavity
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 **
General Life Cycle
Radial Symmetry
- body parts are arranged concentrically
around an oral-aboral axis
oral
aboral
Nematocysts
• specialized stinging organelles
• found within cnidocytes (cells)
• cnidocytes are located in epidermis
A cnidocyte
with a
nematocyst
within it
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
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
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
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
Physiology
Reproduction
Asexual
– budding
– longitudinal fission
– pedal laceration
(e.g. sea anemones)
Physiology
Reproduction
Sexual
– usually dioecious
(separate sexes e.g. humans)
– monoecious
(both male + female gonads in 1 individual)
– results in Planula larva
Phylum Cnidaria
Class Hydrozoa
Class Scyphozoa
Class Anthozoa
Class Hydrozoa
• medusa & polyp body forms
Fire coral
Class Hydrozoa
• medusa & polyp body forms
• most are colonial
 colonies are formed of individual
zooids
a single zooid
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
Class Hydrozoa
- a sessile colony showing polymorphism
gonozooid
entire
colony
gastrozooid
Class Hydrozoa
- a Portugese Man-o-war is a floating hydrozoan
colony showing polymorphism
pneumatophore
entire
colony
gastrozooid
dactylzooid
Class Hydrozoa- life cycle
sexual
reproduction
asexual
reproduction
Class Hydrozoa
• Hydra is an example of a solitary, freshwater hydrozoan
asexual
reproduction
sexual
reproduction
gonads
bud
Class Scyphozoa
• “true” jellyfish
• medusa & polyp body forms
• thick mesoglea
Class Scyphozoa- life cycle
sperm egg
ephyra
strobila
Adult medusa
scyphistoma
larva
Class Anthozoa
• polyp body form ONLY
• all marine
Class Anthozoa
• some are colonial
 colonies are formed of individual
zooids
• some are solitary
Class Anthozoa
Sea anemones
Class Anthozoa
Soft Corals
Sea pen
Sea pansy
Class Anthozoa
Stony Corals
Class Anthozoa- life cycle
Sexual reproduction
sperm egg
larva
Class Anthozoa- life cycle
asexual reproduction
fission
pedal laceration
fission
How does Cnidaria fit in?
Cnidaria
3 classes:Hydrozoa, Scyphozoa, Anthozoa
Porifera
2 body types: polyp, medusa
diploblastic
3 body types
tissue level
choanocytes
of organization
cellular level
of organization
Blastula stage
heterotrophic
multicellular
eukaryote
unknown
common ancestor
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
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
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
Importance of Coral Reefs
• one of the most productive ecosystems
although the water is nutrient-poor
• “hot spots” for biodiversity
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)