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Cnidarians. “ The guys with the stinging tentacles ”. Cnidarians. Finally, we see a pie that can be sliced! Cnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis.
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Cnidarians “The guys with the stinging tentacles”
Cnidarians • Finally, we see a pie that can be sliced! • Cnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis. • Here we also observe a large jump on the evolutionary scale: tissues that perform specific functions.
Phylum Cnidaria The Classes of Cnidaria are: • Anthozoa- Sea Anemones and Corals • Hydrozoa- Hydra • Scyphozoa- “true”jellyfish • Cubozoa- “box-shaped” jellyfish • Ctenophora- non stinging Cnidarians: • Comb Jellies **There are over 10,000 species of Cnidarians
Interesting Stuff 1. Jellyfish fact: Jellyfish have been around for more than 650 million years which means that they outdate the dinosaurs and the sharks. 2. Jellyfish fact: Different species of jellyfish can be found in all the worlds’ oceans. Jellyfish can even be found in freshwater. 3. Jellyfish fact: A species of jellyfish, the Box jellyfish (sea wasp) kills more people than any other marine creature. 4. Jellyfish fact: The worlds largest known jellyfish can reach a diameter of 2.5 m/ 8ft and their tentacles can grow to be half the length of a football field. 5. Jellyfish fact: Jellyfishes uses jet propulsion to make their way through to oceans of the world. Some swim while others mostly drifts with the currents. 6. Jellyfish fact: Some species of jellyfish contain a lot of protein and are thought to be able to play a large role in ending hunger and malnutrition.7. Jellyfish fact: Jellyfish is able to reproduce both sexually and asexually during different parts of their lifecycles8. Jellyfish fact: what enables them to survive is their stinging tentacles that protect them from being preyed upon.
Characteristics of Cnidarians • Two cell layers (epidermis, gastrodermis, separated by jelly-like layer called mesoglea) • Stinging tentacles • Sac-like digestive system • Radial symmetry • Tentacles are arranged in a circle around the mouth • Nerve net- simple nervous system • invertebrate
Radial Symmetry Radial Compass jellyfish
Anatomy A. Polymorphism- Cnidarians have more than one body form: 1. Polyp 2. Medusa
Polyp Form • Tube with tentacles around the mouth • Sessile Coral polyp
Medusa • Umbrella shape • Tentacles around mouth • Motile, Free-swimming
Cnidocytes-Stinging Cells • Within the cnidocyteis the nematocyst (which is like a capsule) • The capsule has the stinging structure which is a hollow thread (Filament) with barbs • Most contain a toxin • Very small, but discharged in large numbers • Usually the sting is only strong enough to kill zooplankton or tiny fish • But there are exceptions!
Discharged nematocysts, • stinging cells used for defense and prey capture, have been the plague of more than fish. • Stings from certain jellyfish have resulted in death in a matter of hours, especially for infants.
Habitat Aquatic: • Most are Marine • A few are freshwater
Two Tissue Layers 1. EPIDERMIS – OUTER LAYER 2. GASTRODERMIS – STOMACH CAVITY MESOGLEA – JELLY MATERIAL BETWEEN TISSUE LAYERS ABUNDANT IN JELLYFISH TO HELP THEM FLOAT
One Opening System WASTES, GAMETES OUT FOOD IN Food enters through the mouth and is digested in thee cells. Wastes are excreted through the mouth. Sperm and eggs are released through the mouth.
Feeding 1. Carnivores (predators) 2. Process of feeding a. Tentacles sting prey with nematocysts b. Tentacles grab prey c. Prey pulled into mouth 3. Prey moved into gastro-vascular cavity (GVC)* 4. GVC makes enzymes, breaks down food, extra-cellular digestion 5. Undigested food moves back out of mouth Lion’s mane eats another jelly!
Process of feeding 3. Prey stuffed into gastro-vascular cavity (GVC)* 4. GVC makes enzymes, extra-cellular digestion 5. Undigested food back out mouth *incomplete digestive tract (no anus)
Respiration • Via diffusion • Body is two cell layers thick
Response • No nervous system • No brain • Nerve net around mouth • Nerves cover the body but do not tell the difference between body parts.
Locomotion • Medusa- motile, free-swimming • Polyps- sessile,attached to hard substrate Exceptions: 1. Hydra tumbles on tentacles 2. Sea anemones glide on pedal disc
Reproduction 1. Asexual budding 2. Sexual a. Medusae release sperm & eggs b. Larvae are free-swimming
Life Cycle of a Typical Cnidarian • Alternation of Generations • One form is the polyp (a cylinder with the closed end attached to the substrate and the open end with the mouth and tentacles directed upward) • The other form is the medusa, free-swimming, with the mouth underneath (like a jellyfish)
Hermaphrodite sexual Life Cycle of a Typical Cnidarian asexual Alternation of Generations
Ecological Role • Predators and prey • Neurotoxins in medical research • Coral – jewelry, building, reefs (surfing!) • Coral reefs - habitat for many different species, great biodiversity, protect coastline E. Symbiosis with other organisms
Do Now • Explain how the jellyfish is adapted for floating? • How do jellyfish capture and digest their prey? • Describe how a typical jellyfish reproduces. • How does the adult form of a jellyfish differ from that of a sea anemone? • How does a sea anemone obtain its food? • How does the sea anemone respond to stimuli?
FORMATION OF CORAL REEFS CORAL REEFS ARE BUILT BY MILLIONS OF CORAL POLYPS OVER THOUSANDS OF YEARS EACH POLYP CREATES A “CUP” OF CALCIUM CARBONATE TO LIVE IN CORALS REPRODUCE ASEXUALLY BY BUDDING, THIS PROCESS HELPS COLONIES TO GROW POLYPS ARE CONNECTED OLD SKELETONS
FORMATION OF CORAL REEFS CORALS ALSO REPRODUCE SEXUALLY ONCE A YEAR BY RELEASING SEX CELLS INTO THE WATER. THIS HELPS TOP ESTABLISH NEW COLONIES
HARD CORALS REEF BUILDERS – USE CALCIUM FOR SKELETON EACH SPECIES HAS A UNIQUE COLONY & CUP DESIGN EXAMPLES: BRAIN, ELKHORN, STAR
Class Scyphozoa: True Jellyfish Fried egg jelly
Portuguese Man 0’ War Tentacles of Physalia physalis
Carukia barnesi: the badest of the bad! Irukandji syndrome: A sting from this little guy can cause the following: “It begins with a mild sting, followed by severe lower back pain, muscle cramps in arms, legs, stomach and chest. It causes sweating, anxiety, nausea, vomiting, headaches and palpitations, and has also been known to cause cardiac failure.”
COMB JELLIES PHYLUM CTENOPHORA BASIC CHARACTERISTICS: “CTEN” REFERS TO FUSED PLATES OF CILIA LOOK LIKE A “COMB” STRUCTURE DO NOT CONTAIN STINGING CELLS USE CILIA TO FILTER WATER TENTACLES ARE STICKY TO CATCH FOOD
Comb jellies: Ctenophora Similar to cnidarians in most respects. Nearly 100 species. Contain cilliary combs which assist in prey capture and mobility.