1. Cnidaria Greek word Cnidos meaning stinging nettles
Phylum
Cnidaria
Greek word Cnidos meaning stinging nettles

2. Cnidarians Their development make it possible for these organisms to:
Swim
Respond to external stimuli
Engulf prey

3. Symmetry of Cnidarians
Cnidarians display Radial Symmetry.
similar parts of the body are arranged and repeated around a central axis
Cephalization – the differentiation of the anterior end of an organism into a definite head (their bodies are not divided into distinct head and trunk)
Examples:
Jellyfish
Corals
Hydra
Sea anemones

4. Medusoid Jellyfish

5. Sea Anemones

6. Coral

7. Hydra

8. Portuguese Man-O-War

9. Structure of Cnidarians
Oral surface
Aboral surface
Centrally located mouth
Tentacles
Cnidarians have two basic forms:
polyp – a sac-like attached stage with the mouth and tentacles oriented upward
Medusa – bell-like, which is like an upside down polyp adapted for swimming

11. Parts of Cnidarians Mouth Gastrovascular cavity
Epidermis – outer layer
Gastrodermis – inner layer of cells lining the gastrovascular cavity
Mesoglea – ranges from a non-cellular, thin membrane to thick jelly-like material between the epidermis and gastrodermis

12. Classes of Cnidarians Hydrozoans Scyphozoans Anthozoans
Freshwater hydra
Portuguese Man-O-War
Some coral such as fire coral
Cubozoans
Box jellyfish
Scyphozoans
Jellyfish
Anthozoans
Sea anemones
Coral

13. Feeding & Digestion of Cnidarians
Most all are Carnivores
Use Nematocysts to capture prey
The stinging cells are called cnidocytes
Two phases of digestion:
Extracellular
Intracellular

14. BEHAVIOR OF Cnidarians
Cnidarians lack a brain or true nerves. They do, however, have specialized nerve cells
Nerve cells interconnect to form Nerve Net.
Cnidarians are diploblasts – they have two germ layers

15. Economical Importance
Cnidarians have little economical importance, however reef-building corals are an exception.
Fish and animals associated with reefs provide substantial amounts of food for humans
Some Asian countries consume jellyfish as a delicacy.

16. Comb Jellies Phylum Ctenophora Resemble that of medusa
Have radial symmetry
Has a gelatinous body that resembles a medusa
Differences they only have two long tentacles but have comb structures and lack stinging cells.

17. Comb Jelly (Ctenophora)