Phylum CnidariaHW: Study notes & Define Vocab

Words.

Intro to Cnidarians How do you say it????

Say it with me now: (ni DARE ee uh) Practicing saying this when you are with your

friends so you sound smart.

What are cnidarians? Examples: Jellyfish & Sea Anemones

Are there many species of cnidarians? Yes, there are 10,000 different species!

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

Body Structure, cont’d The function of the two layers:

Outer Layer: protects internal body Inner Layer: mostly for digestion

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.

What’s that again????

Feeding & Digestion What’s 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 have

threadlike tubes that contain

poison & barbs.

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.

Feeding & Digestion cont’d After prey is hit with a nematocysts or

cnidocytes (tentacles) the cnidarian brings it to its mouth (it’s only opening).

It then eventually makes it’s way to the gastrovascular cavity. Cells in the gastrovascular cavity secrete

digestive enzymes to break down the captured prey.

Any undigested material is then expelled through the mouth. Yummy.

Response to stimuli Cnidarians have a primitive nervous system

known as a nerve net. These specialized cells can cause contractions

of muscle-like tissue. The movement of tentacles during prey capture

is a result of these contractions.

Types of organ systems As we’ve 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.

Comparison of Sponges & CnidariansExample

Body Plan Asymmetrical Radial Symmetry

Feeding/

Digestion

Filter FeederDigestion takes place in amoeboid cells

Captures prey with nematocysts & tentaclesDigestions takes place in gastrovascular cavity

Movement Sessile Aquatic floating or sessile

Response to Stimuli

No nervous systemCells react to stimuli

Simple nervous system consisting of nerve net

Reproduction SexualAsexual: Fragmentation & budding

SexualAsexual: budding

Vocabulary Review -- HW Define the following words using your notes:

Radially Symmetry Sessile Cnidocyst Nematocyst Gastrovascular cavity Nerve net