Transcript Phylum Cnidaria Characteristics

Phylum Cnidaria Characteristics
 1. Radial Symmetry
 2. Diploblastic – meaning that they only have two tissue layers,
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the ectoderm (outer layer, or epidermis) and endoderm (inner
layer, or gastrodermis) and no true organs.
The “jelly” is the middle is not a true mesoderm and is called the
mesoglea.
3.Have a mouth and a primitive stomach called a gastrovascular
cavity. They don’t have an anus, however, so any undigested
food has to come back out through the mouth.
4. Have a nervous system, called a nerve net, but no real brain.
5. Have specialized stinging cells called nematocysts used for
defense and feeding.
6. Have a hydrostatic skeleton (the water serves as a skeleton).
Nematocysts
 When you get “stung” by a jellyfish, it’s the
nematocysts that are stinging you. Think of it as a tiny,
spring-loaded javelin. The pointy part has hollow tips
with a paralytic neurotoxin. And you aren’t the only
one getting stung! Cnidarians use their nematocysts
to paralyze small fish and crustaceans (small animals
with shells) to use for food.
Movement
 Cnidarians fill their hollow center up with water and
then shoot it out again, using their muscle-like nerve
ring, to provide them with locomotion. Because of
this, they can only actively move in the direction their
“bell” is facing.
Bioluminescence
 Many cnidarians “glow”, flash, or emit light when
threatened. The light is used to startle the
predator.
 The light is made by a chemical reaction of
luciferase (an enzyme) and luciferin (the light
maker).
Class Hydrozoa – The Hydra
 Freshwater organism that only has a polyp stage, no
medusa stage.
 Usually found hanging on the underside of floating
plants in streams or ponds.
 Monoecious and reproduce asexually by budding.
The Hydra
Class Scyphozoa - Jellyfish
Reproduction
in Jellyfish
 Jellyfish are dioecious, either male or female, and
reproduce sexually. Jellyfish mature through a process
referred to as alternation of generations. This means
that for the first part of their lives, they exist in the polyp
stage, then change into the medusa stage later on.
 The larva of a cnidarian is called a planula.
 This planula develops into a polyp, the sessile, or sedentary
stage of the animal.
 This polyp then forms buds which detach from the polyp
itself and form the free-swimming medusa stage that we
are familiar with.
Class Cubozoa: Box Jellies
Big Stings Come in Small Packages!
 The Irukandji Jellyfish (Carukia barnesi) is a box
jelly that inhabits the waters of Australia. This is a
deadly jellyfish, which is only 2.5 centimeters (with
bell and tentacles) in diameter, which makes it
difficult to spot.
The Irukandji is believed to be the most
venomous creature in the world. Movie
Phylum Cnidaria, Class Anthozoa - Coral
 Coral reefs are the most complex, species-rich,
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and productive marine ecosystems in the world.
They provide protection to coastlines from storm damage,
erosion, and flooding by reducing wave action.
Serve as protection to many fish and other aquatic species.
Boost the economy in coastal areas due to increased tourism.
Source of building materials.
Within the past thirty years, the number of coral worldwide has
massively declined due to human actions such as pollution,
harvesting for money, and coastal development. The biggest
threat to coral is global warming because the waters are
becoming too hot for the coral to survive and they end up
“bleached”.
Quick Review
 1. Which of the following are true about cnidarians?
 a. They have stinging cells.
 b. They can regenerate lost body parts.
 c. They live only in fresh water.
 d. They include sponges, corals, and hydras.
 2. Cnidarians are either in ______________form or in
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______________form. Both body types have _______________
symmetry.
3. The sea anemone is a polyp. True or False?
4. A cnidarian will always have the same body form for its entire
life. True or False?
5. All cnidarians have a nerve ___________, which controls
movement of the body and tentacles.
6. Jellyfish have a nerve _____________, which coordinates
swimming.