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What do these animals have in common?
Phylum
Cnidaria
“the jellies”
What is a cnidarian?What is a cnidarian?•invertebrates
•more than 9000 species
•jellyfishes, corals, sea anemones, and hydras.
•worldwide
•all but a few are marine
• two distinct body forms during their life cycles
Polyp
Medusa
• polyp = sessile form
•mouth surrounded by tentacles. - sea anemones, corals, and hydras.
• medusa = free-swimming form
- jellyfish
The Medusa
-an umbrella-shaped,
- floating body = a bell, with mouth on underside.
Tentacles
Body FormBody Form
The Polyp
Attached to substrate, mouth on top surrounded by tentacles
mouth
Body FormBody Form
Body formBody formOne body form may be more often seen than the
other.
In hydras, polyp form is most common form of hydras.
In jellyfishes, the medusa form is usually observed.
http://www.microscope-microscope.org/gallery/Mark-Simmons/pages/hydra2.htm
Body formBody form
Most cnidarians undergo a change in body form during their life cycles.
Polyp
Medusa
At some point, most Cnidarians exist as both a polyp and a medusa.
Body structureBody structure
• radially symmetrical
• one body opening
• two cell layers
How is this similar to sponges?
Mouth
Cavity
Bud
Disc Outer cell layer
Jellylike layer
Inner cell layer
Tentacle
Body structureBody structure
• cell layers are organized into tissues with specific functions
- true tissues
- inner layer mainly assists in digestion
-surrounds the GASTROVASCULAR CAVITY
Mouth
Tentacle
Cavity
Bud
Disc Outer cell layer
Jellylike layer
Inner cell layer
Body structureBody structure
• two cells layers allows easy diffusion of:
- Oxygen - dissolved in water, it can diffuse directly into body cells.
- Carbon dioxide /other wastes - moves out of the body cells directly into the surrounding water.
Reproduction in cnidariansReproduction in cnidarians
• sexual and asexual reproduction
Sexual reproduction
•occurs in only in the Medusa phase if it has both forms in life cycle
IF there is NO medusa stage, then the polyp can reproduce sexually.
Male Female
Eggs
Blastula
Larva
Polyp
Asexual Reproduction
Bud
Sexual Reproduction in CnidariansSexual Reproduction in Cnidarians
Both the medusae and
polyps are diploid
(2n)
animals.
Diploid =
2 full sets of
chromosomes
Per body cell
Fertilization
Nematocyst before discharge
Nematocyst after discharge
Digestion in cnidariansDigestion in cnidarians
• Predators
- capture or poison prey using nematocysts
- a capsule that contains a coiled, threadlike tube.
-tube may be sticky or barbed, and may contain toxins
- located in stinging cells that are on tentacles
Digestion in cnidariansDigestion in cnidarians
Once captured by nematocysts, prey is brought to the mouth by contraction of the tentacles.
Mouth
Medusa
Mouth
Gastrovascular cavity
Polyp
• Food enters gastrovascular cavity
• digestive cells release enzymes to break down prey
•undigested materials are ejected back out through the mouth.
Diversity of CnidariansDiversity of Cnidarians
There are four classes of cnidarians:
• Hydrozoa
•Anthozoa
•Scyphozoa
•Cubozoa
Class HydrozoaClass Hydrozoa•2 groups
- hydroids (hydra)
- siphonophores (Portuguese man-of-war)• marine animals
•Most hydrazoans go through both stages
• Hydra - polyp stage only
•reproduce by budding
•found attached to piers, shells, and other surfaces.
#1buddingdevelopmentSea monkeydaphnia
The siphonophores - floating colonies
-drift about on ocean’s surface.
The Portuguese man-of-war, Physalia, is an
example of a siphonophore
hydrozoan colony
Different functions for
different individuals
Class HydrozoaClass Hydrozoa
Class AnthozoaClass Anthozoa
• exhibit only the polyp form.
• Corals
• Sea anemones
• Sea fans
Sea apple feeding
• live in colonies of polyps in warm ocean waters around the world.
• secrete protective, cuplike calcium carbonate shelters around their soft bodies.
•Colonies of many coral species build the coral reefs
•provide food and shelter for many other marine species.
Corals
Corals that form reefs are = hard corals.
• soft corals= do not build calcium carbonate structures – not reef builders.
Corals
Living portion of a coral reef is a thin, fragile layer
•grows on top of the shelters left behind by previous generations.
Often found in
•shallow,
•nutrient-poor waters,
•thrive because of symbiotic relationship with microscopic, photosynthetic protists called zooxanthellae.
Corals
Bleaching Worldwide
•Zooxanthellae
•produce oxygen and food that corals use,
•Uses carbon dioxide and waste materials produced by the corals
•cause bright colors found in coral reefs.
•free-swimming, sometimes leave the corals
•Caused by warming ocean temperatures and
•Increasing acidity due to increased CO2 in atmosphere
•Corals die without them = “bleaching”
•70% bleached in 20-30 yrs; 35 million acres so far
• Coral reefs provide habitat for 25% of marine fish
• About 1 billion people rely on fish as their primary food source
• Tourism – over a billion dollars is spent every year in the Caribbean, Australia (3.9 billion/year), and the Pacific Islands
• 1.2 Billion in Florida each year• Most diverse ecosystem – “Ocean Rainforest”• 4000 species of fish, 800 species of coral
• Corals are used for pharmaceuticals
• Chemical extracts from corals have helped create drugs to treat AIDS, Cancer, Arthritis, Inflammatory disorders, and pain killers
• Beneficial for patients with heart, kidney, and liver transplants.
Class Scyphozoa = jellyfishClass Scyphozoa = jellyfish•Fragile
•sometimes luminescent bodies• Some are transparent
•May be pink, blue, or orange.
Medusa form is the dominant stage in this class.
Class ScyphozoaClass Scyphozoa
• muscle-like cells in outer cell layer can contract
• When these cells contract , the bell contracts
• propels the animal through the water.
Class Cubozoa
• Box jellyfish • Originally included in Class Scyphozoa.• Differences:
– Their bells are square-shaped, instead of round– They have primitive brians– They have eyes– They swim, not float– They sleep
Class Cubozoa
• The Irukandji in Australia is one of the most dangerous animals
• It is very small, only 2.5 cm from bell to tentacles
Giant Jellyfish• Japan has been invaded by Nomura’s
jellyfish – the giant jellyfish.
Research:
• What are Nomura’s Jellyfish?
• Where are they found? Just Japan?
• What causes them to get so big?
• Are they dangerous?
• Are they new? Or are they only now getting noticed?
Giant Jellyfish
• 6.5 ft wide and 450 lbs
• More common in China and Korea
• Only recently in Japan
Giant Jellyfish
• Not much is known, Japan studying mating/migration habits
• Choking fishing nets
• Possible warmer seas (global warming) causes increase in population
• http://video.google.com/videoplay?docid=2208948115892996006&q=giant+jellyfish&total=103&start=0&num=10&so=0&type=search&plindex=0
The earliest known cnidarians also date to the Precambrian, about 630 million years ago.
The earliest coral species were not reef builders, so reefs cannot be used to date early cnidarians.
The larval form of cnidarians resembles protists, and because of this, scientists consider cnidarians to have evolved from protists.
Where did they come from?