Download Phylum Cnidaria

3/26/12
• If both sponges and cnidarians have two layers
of cells, why are they in different phyla?
• Key terms: cnidocytes, nematocysts
Phylum Cnidaria
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Common name : Stinging cell animals
Multicellular with true tissues – some simple organs.
Radial Symmetry
2 body designs:
– Polyp (vase shaped, sessile) - Medusa (bell, free)
• 2 cell layers
– Epidermis (ectoderm)
– Gastrodermis (endoderm)
– Separated by mesoglea (where jellyfish get their
name)
– Digestive system
with one opening
• Special Cell type:
– Cnidocyte (stinging cell)
• Used for defense and feeding
• Nematocyst is released when
cnidocytes are pressured.
(some can be triggered by the
presence of certain chemicals)
They inject toxin into the prey.
Concentrated in epidermis on
tentacles.
• Classification:
– Approximately 9,000 species
– 4 classes:
• Hydrozoa – 2,700 species.
• Both freshwater and marine
• Colonial polyps (some solitary)
• Ex: Hydras, Physalia
• http://video.nationalgeographic.com/video/animals/i
nvertebrates-animals/otherinvertebrates/manowar_portuguese/
• Classes’ cont’d
– Scyphozoa -200 species
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All marine
Solitary
Free swimming or floating medusae (planktonic)
http://videos.howstuffworks.com/discovery/28235assignment-discovery-jellyfish-reproduction-video.htm
• http://videos.howstuffworks.com/discovery/27684assignment-discovery-anatomy-of-a-jellyfish-video.htm
• Class Cubozoa
– Box jellies
– Very toxic
Average life span in the wild:
Less than 1 year
Size:
Tentacles 10 ft (3 m) long; body 10 in (25 cm) across
Weight:
Up to 4.4 lbs (2 kg)
Did you know?
Sea turtles are unaffected by the sting of the box jellyfish and
regularly eat them
Symptoms
• Discuss…
– How are box jellies different from other jellyfish?
– Why is it important to study the evolutionary
relationships of box jellies?
Classes cont’d
• Anthazoa
– 6,000 species
– Corals and anemones
– Polyp dominates (sessile)
– Only marine
– Giant Green Anemone Feeding Video | Monterey
Bay Aquarium