Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu To View the presentation as a slideshow with effects select “View”

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” To advance through the presentation, click the right-arrow key or the space bar. From the resources slide, click on any resource to see a presentation for that resource. From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. You may exit the slide show at any time by pressing the Esc key. How to Use This Presentation

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Simple Invertebrates Chapter 28 Table of Contents Section 1 Sponges Section 2 Cnidarians Section 3 Flatworms and Roundworms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Simplest Animals The bodies of most sponges completely lack symmetry and consist of little more than masses of specialized cells embedded in a gel-like substance called mesohyl. Sponge cells are not organized into tissues and organs. Sponges have a body wall penetrated by tiny openings, or pores, called ostia, through which water enters. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Simplest Animals, continued Sponges also have larger openings, or oscula, through which water exits. Sponges are also sessile. Early in their lives, sponges attach themselves firmly to the sea bottom or some other submerged surface, like a rock or coral reef. They remain there for life. Most sponges are bag-shaped and have a large internal cavity. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Simplest Animals, continued Lining the internal cavity of a sponge is a layer of flagellated cells called choanocytes, or collar cells. As the flagella beat, water is drawn in through the pores in the body wall. Amoebocytes are sponge cells that have irregular amoeba-like shapes. They move about the mesohyl, supplying the rest of the sponge’s cells with nutrients and carrying away their wastes. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Simplest Animals, continued Protistan Ancestors The choanocytes of sponges very closely resemble a kind of protist called a choanoflagellate. Ancient choanoflagellates similar to the one shown here may be the ancestors of sponges. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sponge Diversity Brilliantly colored sponges abound in warm, shallow sea waters. Other marine sponges live at great depths, and a few species even live in fresh water. Rather than being a simple baglike shape, the body wall of some sponges may contain hundreds of folds that are sometimes visible as fingerlike projections. These folds increase a sponge’s size and surface area. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sponge Diversity, continued Sponge Skeletons To prevent the sponge from collapsing in on itself, the sponge body is supported by a skeleton. The skeletons of most sponges are composed of a resilient, flexible protein fiber called spongin. A few sponges have skeletons composed of spicules. A spicule is a tiny needle composed of silica or calcium carbonate. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reproduction Sponges can reproduce asexually through fragmentation and budding. When living conditions become harsh (cold or very dry), some freshwater sponges form gemmules, clusters of amoebocytes encased in protective coats. Sealed in with ample food, the cells survive even if the rest of the sponge dies. When conditions improve, the cells grow into a new sponge. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reproduction, continued Sexual reproduction is also common among sponges. Most sponges are hermaphrodites, meaning they produce both eggs and sperm. Since eggs and sperm are produced at different times, self-fertilization is avoided. Section 1 Sponges Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Two Body Forms Hydras, jellyfish, and corals belong to the phylum Cnidaria. Cnidarians have two basic body forms, and both show radial symmetry. Medusa forms are free- floating, jellylike, and often umbrella-shaped. Polyp forms are tubelike and are usually attached to a rock or some other object. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Two Body Forms, continued Cnidocytes Flexible fingerlike tentacles surround the opening to the gastrovascular cavity of cnidarians. Located on the tentacles are stinging cells called cnidocytes. Within each cnidocyte is a small barbed harpoon called a nematocyst. When triggered, the nematocyst explodes forcefully and sinks into the cnidarian’s prey. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Two Body Forms, continued Extracellular Digestion In cnidarians and all subsequent animal phyla, digestion begins extracellularly (outside the cell), in the gastrovascular cavity. Enzymes break food down into small fragments. Then cells lining the cavity engulf the fragments, and digestion is completed intracellularly. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Hydrozoans Freshwater Hydrozoa Hydras live in quiet ponds, lakes, and streams. They attach to rocks or water plants by means of a sticky secretion they produce in an area of their body called the basal disk. Hydras can glide around by decreasing the stickiness of the material secreted by their basal disk. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Hydrozoans, continued Marine Hydrozoa Marine hydrozoans are typically far more complex than freshwater hydrozoans. Often many individuals live together, forming colonies. The cells of the colony lack the interdependence that characterizes the cells of multicellular organisms. However, they often exhibit considerable specialization. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Hydrozoans, continued Reproduction in Hydrozoans Most hydrozoans are colonial organisms whose polyps reproduce asexually by forming small buds on the body wall. Many hydrozoans are also capable of sexual reproduction. During sexual reproduction, the medusas release sperm or eggs into the water. The gametes fuse and produce zygotes that develop into free-swimming, ciliated larvae called planulae. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scyphozoans Cnidarians belonging to the class Scyphozoa are the organisms usually referred to as true jellyfish. Scyphozoans are active predators that ensnare and sting prey with their tentacles. The stinging nettle, Aurelia, is one of the most familiar jellyfishes. The Aurelia life cycle is similar to that of Obelia. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scyphozoans, continued Jellyfish Relatives Related to the jellyfish are the cubozoans, or box jellies. As their name implies, cubozoans have a cube-shaped medusa. Other relatives are members of the phylum Ctenophora, which includes the comb jellies. Comb jellies differ from true jellyfish in two major ways— they have only a medusa stage and they have no cnidocytes. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Anthozoans The largest class of cnidarians is class Anthozoa. Anthozoans exist only as polyps. The most familiar anthozoans are the brightly colored sea anemones and corals. Anthozoans typically have a thick, stalklike body topped by a crown of tentacles that usually occur in groups of six. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Anthozoans, continued Sea Anemones Sea anemones are a large group of soft-bodied polyps found in coastal areas all over the world. Sea anemones feed on fish and other marine life that happen to swim within reach of their tentacles. Sea anemones often reproduce asexually by slowly pulling themselves into two halves. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Anthozoans, continued Corals Most coral polyps live in colonies called reefs. Each polyp secretes a tough, stonelike outer skeleton of calcium carbonate that is cemented to the skeletons of its neighbors. Over thousands of years, these formations build up into coral reefs where hundreds of thousands of polyps live together on top of old skeletons. Section 2 Cnidarians Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms Although the flatworm body plan is relatively simple, it is a great deal more complex than that of a sponge or cnidarian. Flatworms have a middle tissue layer, the mesoderm. And unlike sponges and cnidarians, the flatworm has tissues that are organized into organs. The flatworm’s body is bilaterally symmetrical and flat, like a piece of tape or ribbon. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Turbellaria Almost all members of class Turbellaria are free- living marine flatworms. However, marine flatworms are rarely studied by students because they are difficult to raise in captivity. Instead, students usually study a freshwater turbellarian such as Dugesia, one of a group of flatworms commonly called planarians. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Cestoda Class Cestoda is made up of a group of parasitic flatworms commonly called tapeworms. Tapeworms use their suckers and a few hooklike structures to permanently attach themselves to the inner wall of their host’s intestines. Tapeworms grow by producing a string of rectangular body sections called proglottids immediately behind their head. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Cestoda A tapeworm’s body consists of a head and a series of proglottids. Each proglottid is a complete reproductive unit, a fact that makes it difficult to eliminate tapeworms once a person is infected. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Trematoda The largest flatworm class, Trematoda, consists of parasitic worms called flukes. Some flukes are endoparasites, or parasites that live inside their hosts. Endoparasites have a thick protective covering of cells called a tegument that prevents them from being digested by their host. Other flukes are ectoparasites, or parasites that live on the outside of their hosts. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Roundworms Roundworms (nematodes) are members of the phylum Nematoda and are characterized by the presence of a body cavity called a pseudocoelom. Movement of the fluid within the roundworm’s pseudocoelom serves as a simple circulatory and gas exchange system. Roundworms have long, cylindrical bodies and are the simplest animals to have a one-way digestive system. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Roundworms, continued Roundworm Infections About 50 roundworm species are plant or animal parasites that cause considerable economic damage to crops and inflict terrible human suffering. Plant roundworms feed on the living plant cells, causing wilting and withering of the plant. At least 14 species of roundworms infect humans. Three sources of human infection are Ascaris lumbricoides, Trichinella spiralis, and members of the genus Necator, commonly called hookworms. Section 3 Flatworms and Roundworms Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 1.What is the name of Phylum W? A.Cnidaria B.Nematoda C.Platyhelminthes D.Porifera Standardized Test Prep Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 2.What is the name of Phylum Z? F.Cnidaria G.Nematoda H.Platyhelminthes J.Porifera Standardized Test Prep Chapter 28

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 3.Where on the key would you find a sea anemone? A.Phylum W B.Phylum X C.Phylum Y D.Phylum Z Standardized Test Prep Chapter 28

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