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 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 & 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

Vocabulary Review -- HW Define the following words using your notes: Radially Symmetry Sessile Cnidocyst Nematocyst Gastrovascular cavity Nerve net