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Download Medusa - Ms. Alger
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Cnidaria 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 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
