1. Essential Question: What is a cnidarian?

2. What are cnidarians?
Soft-bodied, carnivorous animals that have stinging tentacles arranged in a circle around their mouths.
Cnidocyte- stinging cells
Nematocyst- poison-filled stinging structure that contains a tightly coiled dart

3. Body Plan Radially symmetrical
Life cycle includes 2 different-looking stages
Polyp- cylindrical body with arm-like tentacles
Sessile
Mouth points upwards
Medusa- mobile, bell-shaped body with the mouth on the bottom
Both have a body wall that surrounds the gastrovascular cavity (stomach)

4. Feeding Paralyzes its prey
Pulls prey through mouth and into the gastrovascular cavity
Extracellular digestion (in the gastrovascular cavity)
Partially digested food absorbed by gastroderm
Intracellular digestion finishes
Any nondigested material exits through the mouth

5. Respiration, Circulation, and Excretion
Nutrients are transported throughout the body by diffusion
Respire and excretes cellular wastes by diffusion through body walls

6. Response
Nerve net
Statocysts- Specialized sensory cells that determine direction of gravity
Ocelli- eyespots that detect light

7. Movement Sea anemones use hydrostatic skeleton
Medusas move by jet propulsion
Muscles contracts causing the bell-shaped body to fold like an umbrella, pushing water out of the bell

8. Reproduction Asexually- budding into a new polyp or medusa
Sexually- external fertilization producing larva that swims until attaches to a hard surface and becomes a polyp

9. Essential Question: What are the 4 groups of cnidarians?
Types of Cnidarians
Essential Question: What are the 4 groups of cnidarians?

11. Cubozoa- Box Jellyfish
Cube-shaped jellyfish (can be seen from above)
4 evenly spaced out tentacles or bunches of tentacles
Well-developed eyes
Active swimmers and predators
Extremely toxic nematocysts
Examples: sea wasps, habu-kurage, irukandji

12. Scyphozoa- ‘true’ Jellyfish
‘cup animals’
Live primarily as medusas
Largest jellyfish was almost 4 meters in diameter with over 30 meters long tentacles
Ex. Moon jellies (aurelia), Lion’s mane jelly (Cyanea), Crown jelly (cephea cephea)

13. Hydrozoa- Hydras Don’t have a medusa stage, lives as solitary polyps
Polyps can grow in colonies, each are specialized
Ex. Portuguese man-of-war has 1 polyp become balloon-like, keeping the entire colony floating, others produce long tentacles to sting prey, others digest the food, while others make eggs and sperm
Asexual (budding) or sexual reproduction
Some can get nutrients from symbiotic photosynthetic protists
Ex. Portuguese man-of-wars, hydras, obelia

14. Anthozoa- Sea Anemones & Corals
‘Flower animal’
Only polyp stage (no medusa)
Sea Anemones are solitary that live at all depths of the ocean
Many shallow-water species also depend on photosynthetic symbionts
Most corals are colonial and their polyps grow together
Hard coral colonies secrete an underlying skeleton of calcium carbonate (limestone)
Colonies grow slowly and may live for hundreds to thousands of years
Ex. Sea anemone, coral, sea pen

15. Coral ecology Coral reefs provides habitats for many oceanic species
Determined by light intensity, temperature, and water depth
Many coral reefs are suffering due to human activity
Chemical fertilizers, insecticides, and industrial pollutants
Recreational divers physically damaging coral reefs
Overfishing
Coral bleaching- high temperatures (due to global warming) kills the algae that lives in the coral tissues, leaving behind transparent cells revealing white skeletons