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Phylum Cnidaria
Phylum Cnidaria
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Radial symmetry
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Mouth at oral end surrounded by
tentacles
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One opening into and out of
gastrovascular cavity
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Cnidocytes (stinging cell) that
discharge nematocysts (stinger)
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2 body forms - Polyp & Medusa
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Two germ layers (tissue layers)
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Nerve net (no centralized brain)
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Still no circulatory or respiratory
systems
Radial Symmetry
Mouth and Tentacles
Generalized Cnidarian Life Cycle
Cnidocyte Structure and Nematocyst Discharge
Diploblastic - 2 germ layers
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Epidermis - outer covering (ectoderm)
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Mesoglea - middle non-living jelly-like layer
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Gastrodermis - lines gastrovascular cavity (endoderm)
Nervous System
Class Hydrozoa
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Only Class that can be found in both
freshwater & marine environments
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Cnidocytes present only on epidermis
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About 50% of life is spent as medusa and
50% as polyps
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Hydra, Obelia, Man-of-War
Obelia
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Freshwater or marine
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Live in colonies rather than free
living like hydra
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Colonies contain two types of
polyps, feeding and reproductive
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Dual-stage life cycle like other
Cnidarians
Obelia
Reproductive Polyp
Feeder Polyp
Obelia
Class Hydrozoa - Gonionemus
Class Hydrozoa
Physalia
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Commonly called the Portuguese
Man-of-War
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Not a jellyfish or even a single
organism
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Made of a colony of hydrozoans that
perform specialized functions
Class Hydrozoa
Physalia
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Gastrozooids – Feeding & digestion
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Dactylozooids – Prey capture
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Gonozooids – Reproduction
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Pneumatophore – Gas-filled float
Class Hydrozoa
Physalia
Class Scyphozoa
Class Scyphozoa
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True Jellyfish
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Round velum with tentacles arising
from multiple points along edge of
velum
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Passive predators that drift with
currents and seldom chase food
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Thick mesoglea layer (jelly of the
jellyfish)
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All marine
Class Scyphozoa
Aurelia – Moon Jellies
Aurelia Life Cycle
Fig. 13.18
Class Cubozoa
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Medusa form dominant & cube
shaped
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Known as Box Jellyfish
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Tentacles arise at the four corners
from a base called the pedalium
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All marine
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Strong swimmers which prey
primarily on fish
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Stings of some may be fatal within
minutes to humans.
Class Cubozoa
Velum
Pedalium
Tentacle
Class Cubozoa
The Box Jellyfish
Cubozoans have eyes concentrated in 4 spots called rhopalia. They use them to
actively chase down prey rather than simply drifting into food like other
Cnidarians
Class Cubozoa
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The sea wasp is considered to be the
most venomous animal known to
man
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One brush against the skin will inject
enough venom to put a full grown
adult in the hospital for over a week
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Even a full morphine drip can not
relieve the pain
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Total venom amount in animal is
enough to easily kill over 60 adult
humans
Class Cubozoa
Class Cubozoa
Class Anthozoa
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Sea Anemones (solitary) & Coral (colonial)
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Medusa stage absent
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Polyps begin life as female and become
hermaphroditic as they age
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Hermaphrodites release sperm and females
release eggs into the water when conditions
are right (moon & temperature)
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All Marine
Class Anthozoa
Sea Anemone
Symbiosis
Class Anthozoa
Corals
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Colony of interconnected polyps
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Protective skeleton of calcium carbonate
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Polyp retracts when not feeding
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Polyps form large colonies rather than living
alone like the anemones
Zooxanthellae
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Photosynthetic dinoflagellates (brown algae)
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Live in corals
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Mutualism - Provide nutrients for coral by
photosynthesis while gaining a home
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Coral Bleaching - Rising CO2 levels is causing
the acidification of the world’s oceans.
Zooxanthellae can not tolerate low pH and die
Class Anthozoa
Brain Coral
Class Anthozoa
Sea Fan
Class Anthozoa
Pipe Organ Coral
Class Anthozoa
Mushroom Coral
Class Anthozoa
Staghorn Coral
Phylum Ctenophora
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Like other Cnidarians, ctenophores have
radial symmetry, 2 germ layers (2 cell
layers thick instead of one), and a deadend digestive tract with no anus
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Commonly called comb jellies
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Hermaphroditic with external fertilization
in the water
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No polyp/medusa lifecycles as in
Cnidarians (Grow directly into freeswimming organisms) & no cnidocytes
either
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Move via cilia on outer edges of body
(largest animals to move this way)
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Marine predators that feed on plankton
The End