Transcript Cnidarians
Cnidarians Jellyfish, Hydra, Corals, Sea Anemones, Sea Fans and Sea Pens Cnidarians Soft-bodied animals Stinging tentacles Sac Body Plan Tissue Level of Organization Radial Symmetry Two basic body forms: Medusa (bell- shaped) and Polyp (flower-like) Structure Mouth – both entry of food and exit of wastes Tentacles – contain spring-loaded nematocysts to sting and immobilize their prey Tentacles guide paralyzed food into the mouth Gastrovascular cavity – food is digested here nematocysts loaded Discharged Many cnidarians do not have to eat due to symbiotic relationships with autotrophic protists The protists live in the gastroderm of the animal Some cnidarians are so dependent on the relationship that they will die if not kept in bright sunlight Some cnidarians have long, tube-shaped branching gastrovascular cavities They do not need to send wastes back through the mouth; wastes simply diffuse out through the cell walls of the epidermis Cnidarians do not have a BRAIN, but do have nerve nets throughout the body. The NERVE NET is concentrated around the mouth. Cnidarians sense their environments using chemo and touch receptors in the epidermal layer Sensory Receptors Statocysts Simple sensory organs surround the medusa bell 1. statocysts are used for balance 2. Ocelli (eye spots) detect light Cnidarians lack true muscle cells, but have cells that change shape when stimulated by the nerve net – therefore, they can move. The medusa can open and close like an umbrella, allowing it to move by “jet propulsion” when water is forced out of the medusa Asexual Reproduction Polyps produce new polyps or medusae by budding Sexual Reproduction Mature medusa release gametes into the water After fertilization, the zygote becomes a ciliated larvae that swims around Eventually, the larva attaches to a hard surface and grows into a polyp Hydras- a Hydrozoan Spend most of life as polyp Can move with a somersaulting movement Portuguese Man-Of-War A type of hydrozoan that grows in a colony One of the polyps becomes a float to keep the colony on the surface They may produce very long tentacles – the poison in the nematocysts is very strong and causes humans great pain Jellyfish Most of life is as a medusa Box jelly The sting of most jelly fish are harmless to humans, but the tiny, Australian jellyfish can kill you in 3-20 minutes. Sea Anemones + Coral Only have the polyp stage Most ecologically important invertebrates Sea anemones are solitary polyps Sea anemones Clownfish and Sea Anemone – symbiotic relationship –tentacles protect clown fish from predators, clownfish protects tentacles from being eaten Corals Grow in shallow, tropical water Produce skeletons of CaCO3 Most are colonial, creating coral reefs Entire ecosystems revolve around coral reefs Coral reefs also protect the land from the ocean swells and waves Corals produce chemicals to prevent being overgrown by other organisms. Some of these chemicals have been used as anti-cancer medications