1. Phylum Cnidaria

2. Cnidarians - jellyfish, coral, hydra, sea anemone
*Named after the stinging cells found on their tentacles called CNIDOCYTES

3. Cnidarians
Are soft bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths.
The simplest animals to have body symmetry and specialized tissues.

4. General Characteristics
About 9000 species
Simple nervous system
Diploblastic organization
Endoderm
Ectoderm

5. Most Cnidarians have radial symmetry

6. General Characteristics Cont’d-
Either tubular/vase or bell/cup shaped
Only animal with
cnidocytes
Cnidocytes-specialized
stinging cells (on tentacle)
All marine (aquatic)

7. Cnidarians have two body forms:
polyp (vase shaped)               medusa (cup shaped)

8. Body Plan
Cnidarians’ bodies are organized around the gastrovascular cavity, where digestion takes place
GV has a single opening that serves as both mouth and anus

9. Body Plan
Cnidarians typically have a life cycle that includes two different looking stages: a polyp and a medusa.
Polyp: a cylindrical body with arm like tentacles
Medusa: a motile, bell-shaped body with the mouth on the bottom.

10. 2 Layers of Cells
Diploblastic:
Gastrodermis: lines GV cavity
Epidermis: lines the outside of the body (the skin)

12. Cnidarian Body Wall

13. Stinging Cells Have Cnidocytes
Contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and inject a toxin or entangle prey

14. Cnidocyte

16. Feeding Gastrovascular cavity- a digestive chamber with one opening
Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

17. Feeding Cont.

18. Nervous and Movement sensory receptors
Both polyp and medusa have a nerve net
A loosely organized network of nerve cells that together allow cnidarians to detect stimuli
Muscles help in directional movement
& capturing prey

19. Polyp Medusa Life Cycles
Cnidarians have two body forms that are representative of the sexual and asexual life cycles that they undergo.
Polyp
Medusa

20. Polyp Usually attaches to a substrate at the aboral end
Oral end is surrounded by feeding tentacles

21. Medusa Sexual Shaped like an upside-down bowl
Tentacles surround the mouth that is housed underneath the bell

22. Respiration, Excretion and circulation
Following digestion, nutrients are usually transported throughout the body by diffusion.
They respire and eliminate the wastes of cellular metabolism by diffusion through their body cells.

23. Reproduction Both sexual and asexual Sexual
Gametes released into water
Fertilization takes place to create free-swimming planula
Asexual
By budding

24. Generalized Cnidarian Life Cycle

26. Examples Scyphozoa: Jellyfish Anthozoa: Sea anemones & Corals
Hydrozoa: Hydra
Cubozoa: Box Jellies

27. Class Hydrozoa
Ex. Hydras

28. The Hydra is a freshwater cnidarian
What kind of symmetry does hydra have?
Is it a medusa or a polyp?

29. Video of hydra at http://www. microscopyu

31. Includes hydras, fire corals, and Portuguese Man of War
Display alternation of generations
Polyp
Medusa

32. Portuguese Man of War - cnidarian that floats in the water and has long tentacles

33. Class Scyphozoa
True Jellyfish
Small polyp stage during life cycle

35. Class Anthozoa
Polyps that are flower-like
Includes sea anemones, corals, sea whips, and sea fans

37. Coral Reefs are made from the skeletons of cnidarians

38. Coral Characteristics
One of the most biologically diverse places in the world!

39. Coral characteristics
Types of Corals:
Hermatypic – reef forming corals, have zooxanthallae, found in warm, shallow waters

40. Coral Characteristics
Zooxanthallae (type of Protist) form a symbiotic relationship with coral
Zooxanthallae gives coral its color
Coral polyps provide shelter
Zooxanthallae

41. Coral Characteristics
Two main types of corals (con’t)
Ahermatypic – non-reef forming, grow in deep water, are found in polar to tropical waters

42. Coral Characteristics
Coral reproduction
Most are monoecious (hermaphroditic)
External fertilization- release sperm and eggs into the water
Many reproduce by budding as well (forms coral reefs)

43. Reef Structure
Anatomy of a coral polyp

44. Reef Problems
Disease
Warming water temps – may be the cause of coral “bleaching”
Increasing sediments
Human footprints

47. Multimedia
Sponge Images and Videos -
Cnidarian Images and Videos -
General Invertebrate Movies at National Geographic 
--- really good video on the portuguese man of war (under invertebrates)
Hydra Video at