1. Phylum Cnidaria
The Stingers

2. 4 Classes we’ll cover:
• Hydrozoa
• Anthozoa
• Scyphozoa
• Cubozoa

3. Shared Traits
• Radial symmetry
• Carnivorous
• Reproduce sexually and asexually
• Polyp and medusa form
– Polyp: sac-like stage with waving tentacles, nonmotile
and benthic
– Medusa: bell-like stage, hanging tentacles, motile and
planktonic

4. Body Layers & Parts
• Ectoderm/Epidermis: outside layer containing
stinging cells (nematocysts)
• Tentacles: used for food capture, lined with
nematocysts
• Endoderm/Gastrodermis: lines the gut, cells here
aid in digestion (absorption of stung prey)
• Mesoglea: jelly-like substance found between the
above two layers
• Mouth and anus are the same opeining

5. Polyp Phase and Medusa Phase

6. Nematocysts
• Coiled firing cells that shoot toxin into prey
• Most not deadly to humans as they aren’t
usually able to penetrate our skin
• Some fatal

7. Class Anthozoa – Corals

8. Class Anthozoa – Anemones

9. Class Anthozoa – Sea Pens

10. Class Anthozoa – generalities
• Largest group of
Cnidarians
• Stay polyps their
whole lives
• Solitary or colonial
• Example: Sea
Anemones, Corals,
Sea Pens

11. Corals – Special Characteristics
• Hard corals – calcium forming
• Contain zooxanthellae, a
symbiotic dinoflagellate
• Soft corals – less calcium,
more flexible protein structure
• Great Barrier Reef off
Australia-world’s largest living
structure.
• Most corals need shallow, salty
water

12. Anatomy of a Coral Polyp
Corals eat (capture food
using tentacles) as well as
make their own food (via
zooxanthellae)

13. Coral Reef Issues

14. Class Hydrozoa
• Can have just a polyp stage, just a medusa stage, or both
• Can join to form complex colonies, like Portuguese Man O’
War (see next slide)

15. Class Hydrozoa

16. Class Scyphozoa
• Medusa is the
dominant life
stage
• Move with
rhythmic
contractions

17. Class Scyphozoa