Download Jelly Fish Blue

Phylum Cnidaria
• “From a distance I was never threatened, in fact I
was infatuated with its beauty. A large, inviting,
bright blue float lured me closer. As I swam
nearer I could see that hidden from my previous
view was an infrastructure of tentacles, some of
which dangled nearly nine meters below the
water’s surface! The creature seemed to consist
of many individuals and I wondered whether or
not each individual was the same kind of being
because, when I looked closely, I counted eight
different body forms!
• I was drawn closer and the true nature of
this creature was painfully revealed. The
beauty of the gasfilled float hid some of
the most hideous weaponry imaginable.
When I brushed against those silky
tentacles I experienced the most
excruciating pain. Had it not been for my
life vest, I would have drowned. Indeed,
for some time, I wished that had been my
fate.”
• Radial or Biradial
– Advantageous because it allows for
sensory structures are evenly distributed
around the body.
• Tissue level of organization
• Ectoderm forms epidermis (outer layer)
• Endoderm forms gastrodermis (inner
layer)
• Mesoglea contains some cells but does
not have true tissues.
• Cnida: fluid-filled, intracellular capsule
enclosing a coiled hollow tube
• Operculum: lid
• Cnidocil : stimulation of the cnidocil
forces open the operculum and
discharges the coiled tube.
• Specialized cnidocyte
• Used in food gathering and defense
• Armed with spines that penetrate the
prey and release paralyzing toxins
• Other cnidocytes
– Wrap around prey
– Sticky secretions that help in attachment
• Most Cnidarians possess two body
forms in their life histories.
• Polyp
– Asexual and Sessile
– Attaches to a substrate
at aboral end
– Mouth is surrounded by
food-gathering
tentacles
• Medusa
– Dioecious and free-swimming
– Shaped like an inverted bowl with
tentacles hanging
– Mouth faces
downward
– Swims by
pulsations of
the body wall
• Gastrovascular Cavity
– Functions in digestion, respiration,
excretion, and discharge of gametes
– Feed on small crustaceans and fish
– Nematocysts entangle and paralyze prey
– Tentacles shorten which draws food to the
mouth
– Mucus and enzymes dissolve food in the
gastrovascular cavity which are phagocytized
and further digested.
• Hydrostatic skeleton
– Water or fluids in body cavity and against
which contractile elements of the body wall
act.
– Think of a balloon
– Polyps: somersault, glide or inch across
the substrate
– Medusa: swim or float
• Nerve Net
– Simple nervous system
– Nerve cells located below epidermis and
interconnect…this creates a nerve net.
– The net conducts impulses around the
body in response to a localized stimulus.
– Response changes due to stimulus strength.
• Most are separate sexes
• Eggs and sperm are released into
gastrovascular cavity
• Free swimming larva called planula
• Can also bud (become medusa)
Animalia
Cnidaria
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Hydrozoa
Scyphozoa
Staurozoa
Cubozoa
Anthozoa
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Small, relatively common
Mostly marine, some freshwater
Alternation of generations
Nematocysts are only in the
epidermis
• Gametes are released to the
outside
• Mesoglea does not contain cells
• Colonial Polyps
– Individuals are specialized for feeding,
reproduction, or defending the colony
• Ex: Obelia, Gonionemus, Hydra
(freshwater), Portuguese Man of War
• All Marine
• Sessile, oral end looks like medusa
• Crawling larva…very little dispersal
abilities
• ~100 species
• All Marine
• “True Jellyfish”
– Dominant stage in life cycle is the medusa
stage
Most are harmless but some can be very
dangerous to humans
Page Title
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• Medusa is cuboidal
• Tentacles hang from each
corner
• Active feeders and
swimmers in tropical
waters
• Some possess dangerous
nematocysts
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Colonial or Solitary
Lack Medusa
All Marine
External
– radial symmetry
• Internal
– biradial symmetry
• Solitary, large, and colorful
• Some attach to solid substrates, burrow
in soft substrates, or live in symbiotic
relationships
• Some move by thrashing or crawling
along a surface
• Feed on invertebrates and small fish
• Asexual Reproduction: Fragmentation
• Sexual Reproduction
– Monoecious (protandry)
– Dioecious
• Stony Coral
– Look like anemones
– Have a calcium carbonate exoskeleton
that they can retract into when threatened
• Soft Coral
– Do not have the CaCO3 exoskeleton
• Sea anemone/Clownfish
• Coral/Zooxanthellae
– Protists that undergo photosynthesis and
give the coral their color
– Also release carbon to build exoskeletons