1. Anjali Chacko, Michelle Fernandez, Rose Zhang
Cnidarians
Phylum: Cnidaria
Anjali Chacko, Michelle Fernandez, Rose Zhang

2. Cnidarians – Phylum Cnidaria
Marine
Specialized Cells
Cnidocytes – stinging organelles
Solitary or Colonial

3. Two Body Shapes of Cnidarians
Polyp
Dorsal mouth with tentacles
Ex: Hydra
Medusa
Mouth on lower oral surface
Ex: Jellyfish

4. Fig. 33-5
Figure 33.5 Polyp and medusa forms of cnidarians

5. 3 Classes of Cnidarians:
Hydrozoa
EX: Hydras, Hydroids, Portuguese Man-of-War
Polyp dominant/ alternation
Some Colonies
Scyphozoa
EX: Jellyfish
Medusa dominant
Free Swimming
Anthozoa
EX: Sea Anemones, Corals
No medusa
Sessile

6. Examples:

7. Anatomy of Cnidarians Radial symmetry
Hollow sac with mouth and surrounding tentacles at one end
Mouth leads to gastrovascular cavity (digestive)
Mouth – ingests food, expels waste

8. Anatomy of Cnidarians Continued…
Epidermis
Protective covering
Gastrodermis
Lines gut, digestive
Mesoglea
Gelatinous, acellular
Separates epidermis + gastrodermis

9. Feeding in Cnidarians (hydra)
Paralyze prey with Nematocysts
Nematocysts
Stinging cells
In cnidocytes
Stimulated – release coiled, hollow thread
Sticky or long and coil around prey or barbs/spines
Prey then pushed into mouth
Lastly, gastrovascular cavity for digestion
Body motion helps circulate contents

10. Gas exchange/Excretion
Through diffusion
No cell far from surface

11. Response in Cnidarians
Nerve nets
Nerve cells that connect sensory cells in body wall to contractile and gland cells
Cells contacted and entire body responds by crunching in

12. Reproduction in Cnidarians
Asexual
Budding – good conditions
Colony – buds remain on parent
Sexual
Fall or stagnant water
Become males and females
Female – ovary – single egg
Male – testis - sperm
Zygote – may become covered with shell for winter

13. Fig
Figure 33.8 The life cycle of the hydrozoan Obelia