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RADIATAanimals with radial symmetry
PHYLUM CNIDARIA
• Cnidarians
are animals
with
stinging
tentacles
BODY STRUCTURE
• Radial symmetry
• No organ systems
• Nerve net (primitive nervous system)
–Whole body responds no matter
what was stimulated
• Outer membrane, inner membrane
and jelly middle called mesoglea
–Oxygen diffuses right into its body,
CO2 diffuses out
BODY STRUCTURE
• Have sensory organs
–Statocysts…balance organ
–Box jellies have 4 pairs of eyes
See Fig 7.3 pg 126
Hydra
BODY STRUCTURE
• Primitive muscle cells- weak
swimmers
• Incomplete digestive tract- one
opening for waste and food
• Lack all other systems and no
body cavity
• Do have hormones to
communicate between cells
REPRODUCTION
• Some Cnidarians have an
alternation of generations,
vary as to dominant stage
• Medusa is the sexual body plan
• Polyp is the asexual body plan
• Larvae is called planula
See Fig 7.2
pg 125
FEEDING
• Cnidoblasts / nematocysts – stinging cells
– Used in defense and to paralyze prey
– After being triggered these cells cannot be reused so they must be regenerated
• Planktonic version are carnivorous, sessile
version are filter feeders
• Food is digested in the cavity
Cnidaria Taxonomy
• Class Hydrozoa - Siphonophores
• Class Anthozoa – Coral
• Class Cubozoa - Box Jellies
• Class Scyphazoa - Jellyfish
Class Hydrazoa
Portugeuse Man O War,
Hydra
Dominant phase is polyp
Found as colonial
animals or individuals
Individuals of a colony
cannot exist on their own
Class Hydrazoa
• Different polyps have different roles
– Feeding polyps
– Reproductive polyps
– Special tentacle polyps
– Float polyps
Class Anthazoa
• Sea Anemones
– Live as a polyp attached to the substrate
• Coral
– Colonial polyps with a limestone exoskeleton
– Polyps share a stomach
– Feed on plankton and have symbiotic algae that
live in their tissue and give them nutrition
– Build reefs using Ca in the water and CO2 from
their algae
See Figs 7.24, 7.26 pg 138-39
A Zoantharian Coral
Class Scyphazoa
• Spend most of their life as umbrella shaped
medusa
• Size range from cms to meters across
• Typical NJ jellies- moon, purple and lion’s
mane jellyfish
• Population explosions of 100s or 1000s of
these animals is currently a concern
• Major predators include tuna, swordfish,
moonfish, triggerfish and certain kinds of
sea turtles
Aurelia
Moon jellyfish, Aurelia
Fig 7.16, 17 pg 134
Pelagia
Cyanea
Class Cubazoa
• More square shaped than
regular jellies
• Powerful stings that can
kill a human
• Good swimmers
Ecology
•
•
•
•
Important predators
Corals are most diverse places in the ocean
Important food source for some animals
Huge blooms are occurring recently
because of warming ocean temperatures
(??) or because of overfishing (???)
Treatment of Stings
• minimize the number of nematocysts
discharging into the skin
• remove the tentacles that adhere to the skin
by using sand, clothing, towels, seaweed
• meat tenderizer, sugar, vinegar, plant juices
and sodium bicarbonate have all been used
with varying degrees of success.
• Do not use : Methylated spirits, picric acid and
human urine
http://en.wikipedia.org/wiki/Image:Haeckel_Ctenophorae.jpg
Phylum Ctenophora
• Common name….comb jellies
• Unique Characteristics
– Comb plates (not tentacles)
– Medusa stage only
– Luminescence common
– Position of paired tentacles changes
symmetry to biradial
Ecology
• Form a large percent of the plankton
• Can regenerate depending on damage
• Feed on plankton including: larvae,
worms, jellyfish, other comb jellies, and
sometimes small fish.
• Same predators as
jelly group
Image ID: nur01002, National Undersearch Research Program (NURP) Collection Credit: OAR/National Undersea Research Program (NURP)
Difference From Cnidaria
– No alternation of generations (medusa
only)
– No nematocysts have sticky cells
instead
– Biradial symmetry, two tentacles
– Combs not tentacles
– Complete digestive system
Comparison Ctenophora to
Cnidaria
• Similarities
–Nerve net
–Lack of organ systems
–Similar role in marine oceans
Taxonomy Phylum Ctenophora
See Fig 7.28 pg 140
Ctenophoran Comb Jelly
t
Fig 7.28 pg 140
Ctenophore
Comb Jelly
See Fig 7.28 pg 141
Ctenophoran Comb Jelly
Fig. 7.28