1. Phylum Cnidaria

2. Symmetry Radial or Biradial
Advantageous because it allows for sensory structures are evenly distributed around the body.

3. Diploblastic Tissue level of organization
Ectoderm forms epidermis (outer layer)
Endoderm forms gastrodermis (inner layer)
Mesoglea contains some cells but does not have true tissues.

4. Cnidocytes
Cnida: fluid-filled, intracellular capsule enclosing a coiled hollow tube
Operculum: lid
Cnidocil : stimulation of the cnidocil forces open the operculum and discharges the coiled tube.

5. Nematocyst Specialized cnidocyte Used in food gathering and defense
Armed with spines that penetrate the prey and release paralyzing toxins
Other cnidocytes
Wrap around prey
Sticky secretions that help in attachment

6. Alternation of Generations
Most Cnidarians possess two body forms in their life histories.
Polyp
Asexual and Sessile
Attaches to a substrate at aboral end
Mouth is surrounded by food-gathering tentacles

7. Alternation of Generations
Medusa
Dioecious and free-swimming
Shaped like an inverted bowl with tentacles hanging
Mouth faces downward
Swims by pulsations of the body wall

8. Maintenance Functions
Gastrovascular Cavity
Functions in digestion, respiration, excretion, and discharge of gametes
Feed on small crustaceans and fish
Nematocysts entangle and paralyze prey
Tentacles shorten which draws food to the mouth
Mucus and enzymes dissolve food in the gastrovascular cavity which are phagocytized and further digested.

10. Maintenance Functions
Hydrostatic skeleton
Water or fluids in body cavity and against which contractile elements of the body wall act.
Think of a balloon
Polyps: somersault, glide or inch across the substrate
Medusa: swim or float

11. Maintenance Functions
Nerve Net
Simple nervous system
Nerve cells located below epidermis and interconnect…this creates a nerve net.
The net conducts impulses around the body in response to a localized stimulus.
Response changes due to stimulus strength.

12. Reproduction Most are separate sexes
Eggs and sperm are released into gastrovascular cavity
Free swimming larva called planula
Can also bud (become medusa)

13. Kingdom: Phylum: Classes:
Animalia
Phylum:
Cnidaria
Classes:
Hydrozoa
Scyphozoa
Staurozoa
Cubozoa
Anthozoa

14. Class Hydrozoa Small, relatively common Mostly marine, some freshwater
Alternation of generations
Nematocysts are only in the epidermis
Gametes are released to the outside
Mesoglea does not contain cells

15. Class Hydrozoa Colonial Polyps
Individuals are specialized for feeding, reproduction, or defending the colony
Ex: Obelia, Gonionemus, Hydra (freshwater), Portuguese Man of War

17. Class Staurozoa All Marine Sessile, oral end looks like medusa
Crawling larva…very little dispersal abilities
~100 species

18. Class scyphozoa All Marine “True Jellyfish”
Dominant stage in life cycle is the medusa stage
Most are harmless but some can be very dangerous to humans

19. Page Title
Note 1
Note 2
Note 3

20. Class Cubozoa Medusa is cuboidal Tentacles hang from each corner
Active feeders and swimmers in tropical waters
Some possess dangerous nematocysts

21. Class Anthozoa Colonial or Solitary Lack Medusa All Marine External
radial symmetry
Internal
biradial symmetry

22. Sea Anemones Solitary, large, and colorful
Some attach to solid substrates, burrow in soft substrates, or live in symbiotic relationships

23. Sea Anemones Some move by thrashing or crawling along a surface
Feed on invertebrates and small fish
Asexual Reproduction: Fragmentation
Sexual Reproduction
Monoecious (protandry)
Dioecious

24. Coral Stony Coral Soft Coral Look like anemones
Have a calcium carbonate exoskeleton that they can retract into when threatened
Soft Coral
Do not have the CaCO3 exoskeleton

26. Symbiotic Relationships
Sea anemone/Clownfish
Coral/Zooxanthellae
Protists that undergo photosynthesis and give the coral their color
Also release carbon to build exoskeletons