1. Phylum
Cnidaria

2. Phylum Cnidaria jellyfish, hydras, sea anemones, corals carnivorous
radial symmetry
have stinging cells called cnidocytes which contain nematocysts
nematocysts are poison filled harpoons used for catching prey

3. Body Symmetry Radial Symmetry Bilateral Symmetry Posterior end
Dorsal side
Anterior end
Ventral
side
Plane of symmetry
Planes of symmetry

4. Cnidarian Body Plan radial symmetry with tentacles
two stages to life cycle
Polyp
Medusa
body surrounds an internal space, gastrovascular cavity
gastrovascular cavity lined with gastroderm (tissue layer)
epidermis is outermost layer
mesoglea between gastroderm and epidermis (jelly-like)

6. Polyp
Sessile
cylindrical body
mouth faces upwards
tentacles point up

8. Medusa
Motile
bell-shaped body
mouth underneath
tentacles point down

9. The Polyp and Medusa Stages
Epidermis
Mesoglea
Gastroderm
Tentacles
Mouth/anus
Gastrovascular cavity
Mesoglea
Gastrovascular cavity
Mouth/anus
Tentacles
Medusa
Polyp

10. Feeding prey is paralyzed and pulled into the gastrovascular cavity
digestion is extracellular
nutrients are absorbed by gastroderm
nutrients dispersed by diffusion
anything not digested leaves through the mouth/anus

11. Respiration, Circulation, Excretion
all are done by diffusion through the body wall

12. Response specialized cells of the nerve net receive stimuli
nerve net is evenly distributed throughout the body
no true brain
also have cells to determine light intensity and gravity

13. Movement done by hydrostatic skeleton in polyps
done by jet propulsion in medusa (like a water pump)

14. Reproduction: Sexual fertilization is external
separate male and female organisms
zygote forms a free-swimming larva
larva grows into a new polyp
polyp then buds to form new medusa

15. Reproduction: Asexual
polyps reproduce by budding
new polyps may grow off the side of existing polyps
polyp may produce medusas

16. Jellyfish Life Cycle Swimming larva Budding polyp Polyp
Female medusa (2N)
MEIOSIS
Fertilization occurs in the open water, producing many diploid zygotes.
Adult medusas reproduce sexually by releasing gametes into the water.
Egg (N)
FERTILIZATION
Sperm (N)
Each zygote grows into a ciliated larva. The larva eventually attaches to a hard surface and develops into a polyp.
Zygote (2N)
Male medusa (2N)
Young medusa
Swimming larva
The polyp buds to release young medusas.
Budding polyp
Polyp
Haploid
Diploid

18. Jellyfish class Scyphozoa (cup animal)
life is spent mostly in medusa stage
larva and polyp stage are usually the same
reproduce sexually

20. Hydras class Hydrozoa usually grow in colonies
no medusa stage in life cycle of freshwater hydras
may reproduce either sexually or asexually

21. Anemones and Corals class Anthozoa (flower animals)
only have a polyp stage in their life cycle
many are colonial
reproduce sexually (some asexually)
larva forms a new polyp