Introduction to Sponges, Cnidarians, Flatworms, and Roundworms

1. Chapter 28 Simple Invertebrates Section 1: Sponges Section 2: Cnidarians Section 3: Flatworms and Roundworms

2. 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.

3. 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.

4. 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.

5. Section 1 Sponges Reproduction • Reproduction Sponges that reproduce sexually are usually hermaphrodites. Sponges also reproduce asexually.

6. 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.

7. 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.

8. Section 2 Cnidarians Hydrozoans • Freshwater Hydrozoa Freshwater hydras are abundant and attach torocks 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. Section 3 Flatworms and Roundworms Roundworms • Roundworm Infections Roundworms have a pseudocoelom and a one-way gut. Most are free-living, but some are animal parasites.