0692-0692 C26CO BDOL-829900 8/4/04 11:49 PM Page 692 Sponges, Cnidarians, Flatworms, and Roundworms What You’ll Learn ■ You will identify and compare and contrast the characteris- tics of sponges, cnidarians, flatworms, and roundworms. ■ You will describe and evaluate the significance of sponge, cnidarian, flatworm, and roundworm adaptations. Why It’s Important Sponges and cnidarians are important to aquatic biomes. Flatworms and roundworms include many species that carry or cause diseases that affect both plants and animals. Understanding the Photo Marine flatworms, like this Thysanozoon nigropapillosum, move by rhythmic contractions of their longitudinal muscles. The colors and pigment patterns of marine flatworm species vary. This flatworm lives in the Red Sea, which is between the Arabian peninsula and northeast Africa. Visit ca.bdol.glencoe.com to • study the entire chapter online • access Web Links for more information and activities on sponges, cnidarians, flat- worms, and roundworms • review content with the Interactive Tutor and self- check quizzes 692 Marian Bacon/Animals Animals 0693-0697 C26S1 BDOL-829900 8/4/04 12:43 PM Page 693 Sponges 26.1 SECTION PREVIEW Objectives Sponges Make the following Foldable to help you learn Relate the sessile life of the characteristics of sponges. sponges to their food- gathering adaptations. STEP 1 STEP 2 Describe the reproductive Collect 2 sheets of paper and Fold up the bottom adaptations of sponges. layer them about 1.5 cm apart vertically. edges of the paper to form 4 Keep the edges level. equal tabs. Review Vocabulary sessile: permanently attached to a surface (p. 674) New Vocabulary filter feeding STEP 3 Fold the papers and crease well to hold the tabs in place. Staple along the fold. Sponges hermaphrodite Obtaining Food external fertilization Label each tab. Reproduction internal fertilization Structural Adaptations Organize Information As you read Section 26.1, list information on each tab about that sponge characteristic. What is a sponge? Sponges are asymmetrical aquatic animals that have a variety of colors, shapes, and sizes. Many are bright shades of red, orange, yellow, and green. Some sponges are ball shaped; others have many branches. porifera from Sponges can be smaller than a quarter or as large as a door. Although the Greek word sponges do not resemble more familiar animals, they carry on the same poros, meaning life processes as all animals. Figure 26.1 shows a natural sponge har- “passage,” and the Latin word vested from the ocean. ferre, meaning “to carry”; Phylum Sponges are pore-bearers Porifera includes animals with pores Sponges are classified in the invertebrate phylum Porifera, which that allow water means “pore bearer.” More than 5000 species of sponges have been to flow through described. Most live in marine biomes, but about 150 species can be their bodies. found in freshwater environments. Sponges are mainly sessile organisms. Because most adult sponges can’t travel in search of food, they get their food by a process called filter feed- ing. Filter feeding is a method in which an organism feeds by filtering small particles of food from water that pass by or through some part of the organism. How does a sponge get rid of its wastes? Figure 26.1 This bath sponge is dark brown or black in its natural habitat. After harvest, it is washed and dried in sunlight. The living material dies and is rinsed away. Only the sponge’s pale, lightweight framework remains. 26.1 SPONGES 693 Larry Mulvehill/Photo Researchers 0693-0697 C26S1 BDOL-829900 8/4/04 12:44 PM Page 694 A Sponge y/Photo Researchers Figure 26.2 Sponges have no tissues, organs, or organ systems. The body red McConnaughe plan of a sponge is simple, being made up of only two layers of F cells with no body cavity. Between these two layers is a jellylike substance that contains other cells as well as the components of the sponge’s internal support system. Sponges have specialized cells that perform all the functions necessary to keep them alive. Critical Thinking Why are sponges classified as animals? Orange tube sponges A Osculum Water and wastes A Osculum are expelled through the osculum, the large opening at the top of the sponge. A sponge D Pore cell Surrounding 1 cm in diameter and 10 cm tall each pore is a pore cell. can move more than 20 L of Pore cells allow water water through its body per day. carrying food and oxygen into the sponge’s body. Pore cell B Epithelial-like cells These cells E Amoebocytes Located are thin and flat. Epithelial-like between the two cell layers cells They contract in of a sponge, amoebocytes response to touch carry nutrients to other or to irritating cells, aid in reproduction, chemicals. In so Amoebocyte and produce chemicals that doing, they close help make up the spicules pores in the Direction of of sponges. sponge. water flow Collar cells through pores C Collar cell Lining the F Spicules They are interior of sponges are produced by cells derived collar cells. Each collar from amoebocytes, and cell has a flagellum that form the hard support whips back and forth, systems of sponges. The drawing water into the small, needlelike structures sponge. located between the cell layers of a sponge are called spicules. Spicules 694 0693-0697 C26S1 BDOL-829900 8/4/04 12:46 PM Page 695 Cell organization in sponges Like all animals, sponges are multi- cellular, as shown in Figure 26.2 on the opposite page. Their cells are dif- ferentiated to perform functions that Apply Concepts help the animal survive. Read the Why are there more species of marine sponges than Problem-Solving Lab on this page to freshwater sponges? Most sponges live in a marine biome. find out how sponges survive in differ- Is there an advantage for sponges to live in a marine biome ent environments. The functions of rather than in a freshwater environment? A series of state- the different cell types are coordinated ments is provided below. Read them, then answer the ques- in a sponge, but sponges do not have tions that follow. tissues like those found in other ani- Solve the Problem mals. Tissues are groups of cells that A. The internal tissues of marine organisms are isotonic with are derived from the ectoderm, endo- their surroundings. derm, and mesoderm in the embryo. B. Oceans do not have rapid changes in the velocity (rate of Sponge embryos do not develop flow) of water. endoderm or mesoderm, so they do C. Young marine animals often spend the early part of their not have cells organized into tissues. life cycles as free-floating organisms. For some sponge species, if you took a living sponge and put it Thinking Critically through a sieve, not only would the 1. Describe Based on statement A, how might a freshwater sponge’s cells be alive and separated environment vary? How might this be a disadvantage for freshwater sponges? out, but these cells would come 2. Describe Based on statement B, how might a freshwater together to form new sponges. It can environment vary? How might this be a disadvantage for take several weeks for the sponge’s freshwater sponges? cells to reorganize themselves. 3. Infer Using your collective answers, explain why few Many biologists hypothesize that sponge species are found in freshwater environments. sponges evolved directly from colonial, flagellated protists, such as Volvox, described in Chapter 19. More impor- tantly, sponges exhibit a major step in the evolution of animals—the change from a unicellular life to a division of Figure 26.3 labor among groups of organized cells. Sponge colonies can form by asexual reproduction. Infer How would these Reproduction in sponges sponges compare genetically? Could Sponges can reproduce asexually they be considered clones? and sexually. Depending on the species, asexual reproduction can be by bud- ding, fragmentation, or the formation of gemmules. An external growth, called a bud, can form on a sponge. If a bud drops off, it can float away, settle, and grow into a sponge. Sometimes, buds do not break off. When this occurs, a colony of sponges forms, as shown in Figure 26.3. Often, frag- ments of a sponge break off and grow into new sponges. 695 Mickey Gibson/Animals Animals 0693-0697 C26S1 BDOL-829900 8/4/04 12:47 PM Page 696 Some freshwater sponges produce amoebocytes. During reproduction, seedlike particles, called gemmules, sperm released from one sponge can be in the fall when waters cool. The carried by water currents to another adult sponges die over the winter, sponge, where fertilization can occur. but the gemmules survive and grow Fertilization in sponges may be into new sponges in the spring when either external or internal. A few waters warm. sponges have external fertilization— fertilization that occurs outside the Compare and animal’s body. Most sponges have contrast budding and the formation internal fertilization, in which of gemmules. eggs inside the animal’s body are fer- Most sponges reproduce sexually. tilized by sperm carried into the Some sponges have separate sexes, but sponge with water. In sponges, the most sponges are hermaphrodites. A collar cells collect and transfer hermaphrodite (hur MAF ruh dite) is sperm to amoebocytes. The amoe- an animal that can produce both eggs bocytes then transport the sperm to and sperm. Hermaphrodism increases ripe eggs. Fertilization occurs and Figure 26.4 the likelihood that fertilization will the result is the development of In sponges, part of the sexual reproductive occur in sessile or slow-moving ani- free-swimming, flagellated larvae, process is the release mals. Eggs and sperm form from shown in Figure 26.4.