1. Phylum Cnidaria

2. General Characteristics
About 9000 species
Simple nervous system
Called a nerve net. No brain
Has tentacles, sometimes very small that grab prey and pull them to the mouth, thus they are predators.
They might be sessile or motile, or each at different times of their life.

3. General Characteristics Cont’d-
Either tubular or bell shaped
(Polyp or medusa form)
Only animal with
cnidocytes
Cnidocytes-specialized
stinging cells (on tentacle)
All marine (aquatic) except
For a few freshwater examples

4. ____________________________
Cnidarians’ bodies are organized around the (hollow stomach area)gastrovascular cavity, where digestion takes place
GV has a single opening that serves as both mouth and anus

5. 2 Layers of Cells
Diploblastic means that its body developes from 2 layers of cells.
Gastrodermis: lines GV cavity
Epidermis: lines the outside of the body (the skin)

6. In between the two layers is the mesoglea- a jelly-like substance.

7. Cnidarian Body Wall

8. Stinging Cells
Have Cnidocytes which are cells that contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and poison or entangle prey

9. Cnidocyte

11. Feeding
Using tentacles they touch the prey and inject the “poison” into them with nematocysts. This “stuns” or paralyzed the prey. WHY? So it wont tear its tentacles off in the struggle.
Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

12. Feeding Cont.

13. Nervous and Movement Have a nerve net & sensory receptors
Muscles help in directional movement
& capturing prey

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

15. Polyp
Usually attaches to a substrate at the aboral end (the end away from tentacles)
Oral end is surrounded by feeding tentacles
Usually the asexual reproductive form

16. Medusa Sexual Reproductive form (but hermaphroditic)
Shaped like an upside-down bowl
Tentacles surround the mouth that is housed underneath the bell

17. When cnidarians display both forms at some point in their lives, they are said to display dimorphism.

18. _________________________
Both sexual and asexual
Sexual
Gametes (sperm and egg)released into water. Fertilization takes place to create free-swimming larvae
Asexual
By budding

19. Generalized Cnidarian Life Cycle

21. __________________________
Scyphozoa: Jellyfish
Anthozoa: Sea anemones & Corals
Hydrozoa: Hydra
Cubozoa: Box Jellies

22. Class Hydrozoa
Ex. Hydras

23. Includes hydras, fire corals, and Portuguese Man of War

24. Class Scyphozoa
True Jellyfish

25. Cubozoans Similar to Scyphozoans, except that their medusa is cuboidal
Includes the box jellyfish
1 of the 10 most venomous animals on the planet

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