Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 Cnidarians Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What is a Cnidarian? What is a Cnidarian? Cnidarians are soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. They are the simplest animals to have body symmetry and specialized tissues. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What is a Cnidarian? Cnidarians get their name from the cnidocytes, or stinging cells, located along their tentacles. Cnidarians use cnidocytes for defense and to capture prey. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What is a Cnidarian? Within each cnidocyte is a nematocyst—a poison-filled, stinging structure that contains a tightly coiled dart. Trigger Filament Nematocyte Barb Filament Cnidarians are carnivorous animals that have stinging tentacles arranged around their mouths. Stinging cells called cnidocytes are used to capture and paralyze prey. Within each cnidocyte is a stinging structure called a nematocyst. Here, a sea anemone captures a fish that has brushed the trigger of the nematocyst. When an animal touches the trigger of a nematocyst, the filament inside uncoils and shoots a barb into the animal. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What is a Cnidarian? Cnidarians are carnivorous animals that have stinging tentacles arranged around their mouths. Stinging cells called cnidocytes are used to capture and paralyze prey. Within each cnidocyte is a stinging structure called a nematocyst. Here, a sea anemone captures a fish that has brushed the trigger of the nematocyst. When an animal touches the trigger of a nematocyst, the filament inside uncoils and shoots a barb into the animal. Copyright Pearson Prentice Hall

Form and Function in Cnidarians Cnidarians are radially symmetrical. Cnidarians typically have a life cycle that includes two different-looking stages: a polyp and a medusa. Copyright Pearson Prentice Hall

Form and Function in Cnidarians A polyp is a cylindrical body with armlike tentacles. In a polyp, the mouth points upward. Polyps are usually sessile. Many cnidarians have both a polyp stage and a medusa stage. Polyp Copyright Pearson Prentice Hall

Form and Function in Cnidarians A medusa has a motile, bell-shaped body with the mouth on the bottom. Many cnidarians have both a polyp stage and a medusa stage. Medusa Copyright Pearson Prentice Hall

Form and Function in Cnidarians The gastroderm is the inner lining of the gastrovascular cavity, where digestion takes place. Gastrovascular cavity Gastrovascular cavity Many cnidarians have both a polyp stage and a medusa stage. Copyright Pearson Prentice Hall

Form and Function in Cnidarians Both polyps and medusas have a nerve net, a loosely organized network of nerve cells. Nerve cells Cnidarians have nerve nets that consist of many individual nerve cells. Copyright Pearson Prentice Hall

Form and Function in Cnidarians Reproduction Most cnidarians reproduce both sexually and asexually. Polyps can reproduce asexually by budding. In most cnidarians, sexual reproduction takes place with external fertilization. External fertilization takes place outside the female's body. Copyright Pearson Prentice Hall

Form and Function in Cnidarians In the life cycle of Aurelia, a common jellyfish, the female releases eggs into the water, and the male releases sperm. Jellyfishes reproduce sexually by producing eggs and sperm. Depending on the species, fertilization is either internal or external. In Aurelia, fertilization is external, occurring after eggs and sperm are released into the water. Copyright Pearson Prentice Hall

Form and Function in Cnidarians Fertilization occurs in open water. Each zygote grows into a free-swimming larva. Jellyfishes reproduce sexually by producing eggs and sperm. Copyright Pearson Prentice Hall

Form and Function in Cnidarians The larva eventually attaches to a hard surface and develops into a polyp. Copyright Pearson Prentice Hall

Form and Function in Cnidarians The polyp eventually buds and releases young medusas that begin the cycle again. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Cnidarians Groups of Cnidarians Cnidarians include: jellyfishes hydras and their relatives sea anemones and corals Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Cnidarians Jellyfishes The class Scyphozoa contains the jellyfishes. Jellyfishes live their lives primarily as medusas. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Cnidarians Hydras and Their Relatives The class Hydrozoa contains hydras and related animals. Hydras differ from other cnidarians in this class because they lack a medusa stage. Instead, they live only as solitary polyps. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Cnidarians Sea Anemones and Corals The class Anthozoa contains sea anemones and corals, animals that have only the polyp stage in their life cycle. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ecology of Corals Ecology of Corals Worldwide distribution of corals is determined by a few variables: temperature water depth light intensity Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 The characteristic that defines the cnidarians is bilateral symmetry. stinging cells. a gastrovascular cavity. cephalization. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 Which of the following statements is generally true of polyps and medusas? Polyps are sessile, and medusas are motile. Polyps are motile, and medusas are sessile Both polyps and medusas are sessile. Both polyps and medusas are motile. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 During the life cycle of Aurelia, the zygote grows into a free-swimming polyp. larva. medusa. gemmule. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 Cnidarians, such as the sea anemone, move using water currents. an exoskeleton. a hydrostatic skeleton. an endoskeleton. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 26-3 The stinging cells found in all Cnidarians are called choanocytes. cnidocytes. polyps. medusas. Copyright Pearson Prentice Hall

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