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Phylum CnidariaHW: Study notes & Define Vocab

Words.

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Intro to Cnidarians

How do you say it????

Say it with me now: (ni DARE ee uh)

Practicing saying this when you are with yourfriends so you sound smart.

What are cnidarians?

Examples: Jellyfish & Sea Anemones

Are there many species of cnidarians?

Yes, there are 10,000 different species!

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Body Structure

Like sponges, they have:

One body opening

Two cell layers Unlike sponges:

Their cell layers are organized into tissues that

have specific functions.

They have symmetry

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Body Structure, contd

The function of the two layers:

Outer Layer: protects internal body

Inner Layer: mostly for digestion

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Cnidarian Symmetry

Cnidarians are radially symmetrical. Remember what that means????

Radially symmetrical organisms can detect& capture prey from any direction. This is especially helpful for the sessile & slow

moving cnidarians.

Some cnidarians are aquatic floaters. Others are sessile.

Whats that again????

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Feeding & Digestion

Whats a jellyfish look like?

They have long, stinging

tentacles. The tentacles have stinging cells

called cnidocytes. (NI duh sites).

They also have nematocysts.

These are capsules that havethreadlike tubes that contain

poison & barbs.

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The nifty nematocyst

Nematocysts are like harpoons.

They are propelled by osmotic pressure (water

pressure).

When a cnidarian is touched or otherwise

stimulated water rushes into the nematocyst (by

osmosis) and increases the water pressure,

forcing the barb out of the nematocyst. The force is so strong that the barb can

penetrate a crab shell.

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Response to stimuli

Cnidarians have a primitive nervous system

known as a nerve net.

These specialized cells can cause contractionsof muscle-like tissue.

The movement of tentacles during prey capture

is a result of these contractions.

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Types of organ systems

As weve mentioned Cnidarians have:

A primitive digestive system

A primitive nervous system

They do not have:

A circulatory system

A respiratory system

Excretory system

So while they are more complex than a sponge,

they are still not very complex creatures.

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Comparison of Sponges & Cnidarians

Example

Body Plan Asymmetrical Radial Symmetry

Feeding/

Digestion

Filter Feeder

Digestion takes place in

amoeboid cells

Captures prey with

nematocysts & tentacles

Digestions takes place in

gastrovascular cavity

Movement Sessile Aquatic floating or sessile

Response

to Stimuli

No nervous system

Cells react to stimuli

Simple nervous system

consisting of nerve net

Reproduction Sexual

Asexual: Fragmentation & budding

Sexual

Asexual: budding

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Vocabulary Review -- HW

Define the following words using your notes:

Radially Symmetry

Sessile Cnidocyst

Nematocyst

Gastrovascular cavity

Nerve net