1. Presented by Louis Perkins
Cnidaria
Presented by
Louis Perkins

2. Facts
Contains over 9000 species of animals found exclusively in aquatic environments
Some specialists recognize only 3 classes, though 4 are generally accepted:
Anthozoa, Cubozoa, Hydrozoa, Scyphozoa

4. General Characteristics
Diploblastic
Radial Symmetry
No body cavity – Acoelomate
Heterotrophic
Sexual and asexual reproduction
Ectothermic
No cephalization
Single orifice used for digestion and respiration

5. Cnidaria have no brains or central nervous systems
Have nerve nets consisting of sensory neurons that generate signals in response to various types of stimulus, such as odors, motor neurons telling muscles to contract, and cilia.
Connected by intermediate neurons

6. Cnidocytes
All Cnidarians at least one type of cnidocyte (from which the name is derived)
Nematocysts – used to capture prey by injecting venom
Spirocysts – used to capture prey by entanglement (only Athozoa)
Ptychocysts – used to build protective tubes for owners to live (only certain Anthozoans)

7. Basic Structure
Members of Cnidaria exist in two forms: Polyp and Medusa

8. Many of the Cnidaria can alternate between these two forms

9. Reproduction
Often involves a complex life cycle with both polyp and medusa stages
Sperm and ova are ejected into water
After fertilization, larvae, called planulae, form
Planulae find suitable location and hook themselves to sea floor
Either stay as a polp or strobilates to produce multiple medusa forms

10. All known Cnidaria can reproduce asexually by various means – budding, segmentation, regeneration

12. Feeding Nematocysts inject poison into prey – triggered by cilium
Tentacles and/or cilia move food into gastrovascular cavity through the mouth
Nematocysts can continue to fire even when the tentacle is detached

14. More Feeding
Prey includes bacteria, protozoans, zooaplankton, fish, or other aquatic creatures
Many species also contain zooxanthellae, photosynthetic protists or zoochlorellae, photosynthetic algae, within body cells
Some species absorb organic compounds from the water

15. Movement
Medusae swim by a form of jet propulsion: muscles squeeze water out of cavity
Not enough power to swim against currents and just enough to control movement within currents
Hydras and some sea anemones can move slowly by creeping like snails, crawling like inchworms or somersaulting.
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16. Importance to Humans
Jellyfish stings killed about 1,500 people in the 20th century
Jellyfish considered delicacies in Asian cultures
Coral reefs are economically important as providers of fishing grounds, protectors against currents and tides, and centers of tourism
The "sea wasp” Chironex fleckeri has been described as the world’s most venomous animal is held responsible for 67 deaths

17. Questions

18. Cnidaria fall under which category of symmetry?

19. What are the two body types of Cnidaria?

20. Fire coral fall under which class of Cnidaria?

21. Which type of cnidocyte contains poison?

22. Are Cnidarians diploblastic or triploblastic?

23. True or False: Chironex fleckeri is a species of coral

24. Thank You!!