Presentation on cnidarians

1. Phylum Cnidaria
Hydra, jellyfish, coral, & seaHydra, jellyfish, coral, & sea
anemonesanemones

3. • They have simple tissuesThey have simple tissues
• No respiratory or excretoryNo respiratory or excretory
system.system.
• The simplest animals withThe simplest animals with
nerve cellsnerve cells..
• Some of them have sensorySome of them have sensory
organs.organs.

4. The simplest animals with sense organsThe simplest animals with sense organs
(statocysts –balance- and ocelli –eyespots-)(statocysts –balance- and ocelli –eyespots-)

5. –They have anThey have an internal body cavity: theinternal body cavity: the gastrovascular cavitygastrovascular cavity
in whichin which extracellular digestionextracellular digestion occurs.occurs.
–The cavity hasThe cavity has a single openinga single opening (it’s both mouth and anus)(it’s both mouth and anus)
–TentaclesTentacles around the opening.around the opening.

6. SpecialSpecial stinging cellsstinging cells ((cnidocytescnidocytes) that contain a) that contain a
specialized stinging organelle, thespecialized stinging organelle, the nematocystnematocyst areare
abundant on tentaclesabundant on tentacles. Coiled thread discharges like a. Coiled thread discharges like a
harpoon. It contains neurotoxin that paralyze preysharpoon. It contains neurotoxin that paralyze preys

10. –Two typesTwo types according to their body shape:according to their body shape:
–Polips (cylindrical and attached to floor)Polips (cylindrical and attached to floor)
–Medusae. (umbrella-shaped, gelatinous andMedusae. (umbrella-shaped, gelatinous and
free-swimming with hydrostatic skeleton)free-swimming with hydrostatic skeleton)

11. –They move with the water currents or byThey move with the water currents or by
contracting their body.contracting their body.

12. - Sea anemones and corals are all polyps with no
medusa stage.
- Some have an exoskeleton or endoskeleton of chitin,
calcium or proteins.

13. • CnidariaCnidaria
– All are aquatic and mostly marine.All are aquatic and mostly marine.
– Radial symmetryRadial symmetry..
– Reproduction is either asexual (most polyps) or sexualReproduction is either asexual (most polyps) or sexual
(medusa)(medusa)
– A planula larva may be present.A planula larva may be present.

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15. Class HydrozoaClass Hydrozoa
–HydraHydra are freshwater solitary polyps.are freshwater solitary polyps.

17. Class AnthozoaClass Anthozoa
• 1.1. Sea AnemonesSea Anemones
– a. They attach to shells, rocks, wood, etc.; some burrow in mud ora. They attach to shells, rocks, wood, etc.; some burrow in mud or
sand.sand.

18. –Some have a mutualistic relationship with hermit crabs.Some have a mutualistic relationship with hermit crabs.

19. Clown fish with sea anemone

21. Class AnthozoaClass Anthozoa
• 2. Corals2. Corals
– They are miniature sea anemones that live in calcareousThey are miniature sea anemones that live in calcareous
cups they have secreted.cups they have secreted.
– They form most coral reefs. These corals require fullThey form most coral reefs. These corals require full
salinity, warmth and light, limiting them to waterssalinity, warmth and light, limiting them to waters
between 30 degrees north and south.between 30 degrees north and south.

24. Class Scyphozoa: True Jellyfish
Fried egg jelly

25. Jellyfish