What do these animals have in common?

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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?