phylum cnidaria
DESCRIPTION
Phylum Cnidaria. HW: 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 - PowerPoint PPT PresentationTRANSCRIPT
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