Cnidaria
By: Michael Dang
Annie Ma
David Shia
http://scrapetv.com/News/News%20Pages/usa/images-3/Nomura-jellyfish-3.jpg
Phylum
Phylum: Cnidaria
Families:
• Hydrozoa- polyp and medusa stages in
reproductive cycle (Ex: corals)
• Scyphozoa- reduced polyp stage (Ex: jellies)
• Cubozoa- box shaped polyps (Ex: box jellies)
• Anthozoa- no medusa stage (Ex: corals)
Sample Animals
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Jellyfish
Corals
Hydras
Box Jellyfish
Anemone
Sea Wasp
Sea Pens
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http://www.biology4kids.com/misc/photos/cnidaria1.jpg
Body Cavity
• Single Body Cavity diploblastic (two membranes:
ectoderm/endoderm) used for digestion and
respiration
• They contain one cavity that operates as both
their mouth and anus
• Polyp- mouth cavity is on top
• Medusa- mouth cavity is on bottom
Body Symmetry
• Radial Symmetry
http://www.uic.edu/classes/bios/bios100/labs/radial.jpg
Nervous System
• Cnidaria lack a brain and a central nervous
system, but they do have a net of neurons
• Ocelli: organs that sense direction of light
• Statocysts: means of regulating tilt and
acceleration in cnidaria
Circulatory System
• None
Digestive System
• All are carnivorous
• Absorb nutrients by filtering water
• Tentacles put the prey into the mouth where
digestive enzymes are used to break prey
down into organic substances
Excretory System
• Present
• Anus/ mouth
• Diffusion
Locomotion/ Musculature
• Has muscle, but really weak in most Cnidaria.
Strong enough to direct movement in a
current
• Jet Propulsion: water is squeezed and then
released from the cavity using coronal muscles
• Some sea anemone can creep along
Skeletal Type
• Cnidaria bodies are composed of the jelly-like
substance called mesoglea
• Most can form a hydrostatic skeleton, in which
the cavity fills with water, expanding the body
of the cnidaria
• Coral have exoskeletons composed primarily
of calcium
http://biology.unm.edu/ccouncil/Biology_203/Images/SimpleAnimals/cnidariaDiagram.jpeg
Sensory Structures/ Features
• Simple sensory structures
• Responds to touch through cnidocytes,
stinging cells located on the tentacles
• Nematocytes, the stinging capsule of a
cnidocyte, releases a poisonous thread when
triggered by a chemical or touch
http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb5pg2_files/cnidocyte.gif
Reproduction
• Sexual and asexual reproduction
• Cnidaria usually have 2 main forms in their life
cycle: the polypoid stage is diploid, and the
mature polyp is usually found in colonies.
Medusae are produced asexually through
budding, which reproduce sexually to form
polyps.
http://www.palaeos.com/Invertebrates/Cnidaria/Images/obelia_cycle.gif
Gas Exchange
• Cnidarians lack the organs for gas exchange,
so they just let the gas from the water diffuse
through their bodies
Other
• The amount of poison from a sea wasp, a
cubozoan, is powerful enough to kill 60
people!
• Coral is really a colony of really small polyps!
• Many species of jellyfish are bioluminescent!
QUIZ TIME
1. What are the two forms of a Cnidaria’s life
cycle?
a. Polyp and Cnidocyte
b. Medusae and Polyp
c. Polyp and Hydrozoa
d. Cubozoa and Medusae
e. None of the above
Answer
• Medusae and Polyps
• Medusae= tentacles
facing down. Motile.
• Polyp= tentacles facing
up. Stationary.
QUIZ TIME
2. What mechanism do Medusae use to move
through the water?
a. Current
b. Jet Propulsion
c. Latching on to other animals
d. A and B are both correct
e. All of the above
Answer
• Current and Jet
Propulsion
• Medusae have relatively
weak muscles, so they
must use the current to
help them move
• Jet Propulsion= uptake
and release of water to
create the thrust force
to make them move
forward.
QUIZ TIME
3. What is the Mesoglea?
a. The excretory waste of the Cnidaria
b. The nervous system of the Cnidaria
c. The name of the colonies that the polyps
form
d. The tentacles of the jellyfish
e. The substance that the Medusae’s body is
composed of
Answer
• The substance that the
Medusae’s body is
composed of
QUIZ TIME
4. What systems are absent in Cnidaria?
a. Skeletal and Nervous
b. Excretory and Digestive
c. Nervous and Circulatory
d. Circulatory and Digestive
e. Musculature and Reproductive
Answer
• Nervous and Circulatory
• Cnidaria have no brains,
thus no nervous system,
but do have a simple
sensory network
throughout the body.
• They do not need a
circulatory system and
regulate substances
through diffusion.