1. Introduction to CNIDARIANS
Biology 11
Mrs. Trevelyan

2. Cnidaria 1. PRESCRIBED LEARNING OUTCOMES and VOCABULARY 2. VIDEOS:
-None 
3. TEXTBOOK PGS
Section 26.2 pgs

4. Examples of Members:

5. Overview…

6. A Breakdown of Cnidarians…
Includes jellyfish, sea anemones, coral, and hydra

7. 1. Unifying Characteristics
Radial symmetry only
Development of body layers (2 total! Outer and inner)
Have a gastrovascular cavity with one opening
Development of tissues (e.g. nerve, muscle and digestive tissue)
Mobility! Some (like jellylfish) can swim; others (like sea anemones) are sessile.

8. 2. Structure Has 2 cell layers with a jellylike substance inbetween
1)epidermis - outer layer
2) endodermis - inner layer
Has a mouth, tentacles, and a gastrovascular cavity
Still no brain, heart or blood

9. 2. Structure Exist in one of two forms:
cylinder-shaped polyp (sessile)
Umbrella-shaped medusa (mobile)

10. 3. Digestion
Have a single opening (“mouth”) and a digestive cavity (“stomach”)
Use tentacles to catch and paralyze prey. Tentacles have called NEMATOCYSTS that use stingers to sting prey
Tentacles move food to mouth where it enters the gastrovascular cavity. Food is then digested and absorbed into the body

11. 4. Respiration/Excretion
No respiratory glands/organs.
Use diffusion at the cell level for gas exchange
EXCRETION
No excretory glands or organs
Solid wastes pass out through the “mouth”
Gaseous wastes are eliminated by diffusion

12. 5. Nervous System
Have a very simple web-like nervous system made up of a nerve net (sensory neurons- touch and smell)
Have groupings of nerves called ganglia
No brain or central nervous system
Can respond to stimuli

13. 6. Reproduction Asexual Reproduction:
Occurs at either the polyp or medusa stage using BUDDING
Cnidarians that stay in the polyp stage (e.g. sea anenomes) also reproduce sexually as polyps

14. 6. Reproduction SEXUAL REPRODUCTION
Usually occurs during the medusa stage
Male and female medusa release eggs and sperm
Fertilization occurs and a free- swimming larvae forms
The larvae attaches to a rock and forms a polyp
See figure 26.7 pg 700

15. 6. Reproduction
SEXUAL REPRODUCTION

16. 7. Additional Interesting Facts
Many organisms feed on and live in coral and sea anenomes (for protection)
Important resources for people (fish and coral reefs)
Protects coastal areas from damage (errosion)
Problem Today: Jellyfish Blooms (increase in pop’n)