Essential Question: What is a cnidarian?

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

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)

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

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

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

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

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

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

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

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)

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

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

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