Wize University Biology Textbook > Invertebrates (Part 1: Non-Molting)
Cnidarians (Jellyfish)
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Cnidaria (Jellyfish)
Cnidarians are both beautiful and powerful with the evolution of their harpoon-like cnidocytes that they use to capture prey. Coral reefs represent some of the most attractive and bio-rich habitats in the world.
- Eumetozoa: True differentiated tissues (muscles and nerves)
- Diploblastic
- Contains Organs: collection of specialized tissues that perform a specific task
- Radial Symmetry
- Contains Jellyfish, hydras, sea anemones and corals
- ~10,000 species
- Mostly marine
- Simple body plans
Two basic forms
- Polyp
- Sessile
- Attached to something (sand, rock etc.)
- Mouth points up
- Have gastrovascular cavity
- Medusa
- Motile
- Uses a hydrostatic skeleton
- Mouth points down
- Most transition from polyp to medusa in life cycle
Cnidocytes
- Carnivores
- Cnidocytes: unique cells used for offense / defense
- Complex endocellular structure
- Nematocyst: most common type of cnidocyte
- Used for defense and prey capture
- Cells are activated by touch
- Nematocyst shoots out (like a spring powered harpoon!)
- Sticks, stabs and poisons prey
- Captured prey are digested in gastrovascular cavity
Ecological Significance
- Many host symbiotic algae (zooxanthellae)
- Predators of zooplankton and larval fish
- Some produce toxins dangerous to humans
- Some construct reefs with coral
- Used for shelter and food
- Anthozoa: Secrete calcium carbonate to form hard skeleton
- Large human tourist economy
- Coral Bleaching: ecological meltdown, mass coral die-offs
- Loose symbiotic algae and die
Coral Bleaching
Practice: Cnidarians
Which of the following is true about cnidarians? (select all that apply)
Practice: Cnidarians
Fill in the blanks.
______________ is a type of ______________________ which functions like a harpoon for offense and defense.