Transcript Describe
Chapter 28 Simple Invertebrates Section 1: Sponges Section 2: Cnidarians Section 3: Flatworms and Roundworms Section 1 Sponges Objectives: •Summarize the general features of sponges. •Describe how sponge cells receive nutrients. •Describe how a sponge's body is structurally supported. •Distinguish between sexual and asexual reproduction in sponges. Section 1 Sponges The Simplest Animals •Sponges Sponges lack symmetry and tissues. Sponges are sessile filter feeders that draw sea water through pores into an internal cavity, trapping tiny aquatic organisms. •Protistan Ancestors Ancient choanoflagellates may be the ancestors of sponges. Section 1 Sponges Sponge Diversity •Sponge Skeletons The sponge’s supportive skeleton is composed of soft spongin fibers, hard spicules, or a combination of both. Section 1 Sponges Reproduction •Reproduction Sponges that reproduce sexually are usually hermaphrodites. Sponges also reproduce asexually. Section 2 Cnidarians Objectives: •Describe the two cnidarian body forms. •Summarize how cnidocytes function. •Summarize the life cycle of Obelia. •Compare three classes of cnidarians. •Compare asexual and sexual reproduction in cnidarians. Section 2 Cnidarians Two Body Forms •Body Forms Cnidarians are radially symmetrical, with bodies made up of tissue. Their body form may be a medusa or a polyp. •Cnidocytes Cnidocytes are stinging cells found in the tentacles of cnidarians. Harpoon-like nematocysts are located within the cnidocytes. •Extracellular Digestion Digestion begins extracellularly in the gastrovascular cavity. Section 2 Cnidarians Hydrozoans •Freshwater Hydrozoa Freshwater hydras are abundant and attach to rocks or water plants by means of a sticky secretion. •Marine Hydrozoa Marine hydrozoans are more complex than freshwater hydrozoans and often form colonies. •Reproduction in Hydrozoans Most hydrozoans are colonial organisms that reproduce asexually, though many forms can also reproduce sexually. Section 2 Cnidarians Scyphozoans •Characteristics Jellyfish are active predators, and some have extremely potent toxins within their nematocysts. Jellyfish spend most of their lives as medusas and usually reproduce sexually. •Jellyfish Relatives Jellyfish are related to the cubozoans or box jellies. Section 2 Cnidarians Anthozoans •Sea Anemones Sea anemones and corals have thick, stalklike polyp bodies. Their life cycle includes no medusa form. •Corals Coral polyps live in colonies called reefs. Section 3 Flatworms and Roundworms Objectives: •Compare the three classes of flatworms. •Summarize the life cycle of a blood fluke. •Describe the body plan of a roundworm. •Summarize the life cycle of the roundworm Ascaris. Section 3 Flatworms and Roundworms Flatworms •Turbellaria Most flatworms, such as planarians and marine flatworms, are free-living. •Cestoda Tapeworms are intestinal parasites that absorb food directly through their skin. •Trematoda Flukes are endoparasitic flatworms. They have a protective covering called a tegument that keeps them from being digested by their host. Section 3 Flatworms and Roundworms Roundworms •Roundworm Infections Roundworms have a pseudocoelom and a one-way gut. Most are freeliving, but some are animal parasites.