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Q How is this sea slug similar to a spider? Both sea slugs and spiders are invertebrates. Invertebrates, which are animals without backbones, account for the vast majority of animals on Earth. You are surrounded by invertebrates on a daily basis, whether you are aware of them or not. Invertebrates exist in a wide variety of shapes and sizes and live in many different habitats, which can include your body!

RE a d IN g T o o lb o x This reading tool can help you learn the material in the following pages.

USING LANGUAGE Your Turn Describing Space Describing an object accurately is Practice using spatial words by completing the activity not as easy as it may seem. Certain words, called spatial below. words, can help you describe the shape and position of 1. Look around your classroom, and choose an object to an object. Spatial words include perpendicular, parallel, describe. diagonal, horizontal, and vertical. 2. Without revealing what the object is, use spatial words to help a partner draw the object you have chosen.

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F homeobox homeotic collagen VOCABULARY 8 molecular, anddevelopmental and homologies, includinganatomical, fossil record, biogeography, and among groups isprovided by the how evidence ofcommon ancestry animals bacteria, protists, fungi,plants, and taxonomic groups, including archaea, whales 24 meters inlength. SEM; magnification 170 from microscopic rotifers (colored vary widel IGURE C Unit 8:Animals compar

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skeleton that many animals to use move entire their bodies. animal’s body. forms also Collagen an integral of part jointed the glue cells inplace, it so is possible for cells to move within the foruse support. Unlike collagen the wall, acell network not does formfibers an extracellular network that many animal cells to form ropelike that fibers are strong both and flexible. These hair. Individual collagen proteins combine with one another contain collagen include skin,bone, ligaments, fingernails, and stranded protein unique to that animals. parts Animal body functions inanimals? these out carries component What support. rely on of rigidity the cells their for structural Therefore, walls. cell lack rigid animals cannot Unlike cells of the plants and fungi, animal cells by Cells CollagenAnimal Are Supported multicellularity independently. ancestors, it is likely that evolved they trait the of Although animals and share fungi heterotrophic do notfungi have same the diversity of functions that animal cells have. cellular. Fungi are multicellular also and organisms use for But food. cells of process larger than particles asingle can food cell engulf. simplest animal is built of many animals cells, all can ingest specialized and source. Single-celled protists eat also other organisms. But even the because compound an animal incellular uses respiration has to come from an outside eat other organisms to gain nutrients the toAny need survive. they organic organisms make own their animals All food. are heterotrophs, meaning they Animals must eat. Their cells lack chloroplasts the that let photosynthetic Heterotrophs AreAll Multicellular Animals ancestor. common characteristicsThese suggest that animals all are descendants the of asingle characters, or heritable features, that apart them set from other eukaryotes. distinguish animals from other organisms? animals All share of aset derived Given huge the physical diversity among animals, what characteristics single spot, endlessly straining water microscopic to collect of particles food. mucus trails insearch of Othersspendwhole their food. adult lives to a fixed detritivores inmost ecosystems. burrow, Some walk, fly, swim, or slide along on pl MAI ants and do not fungi live. are They dominant the herbivores, predators, and Anim Animals are found including on nearly Earth, places everywhere where Collagen N

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Animals Are Diploid and Usually Reproduce Sexually FIGURE 1.3 In the wild-type fly Animals are the only multicellular organisms that do not alternate between (top), the antennae develop nor- free-living diploid and haploid stages. In all animal species, the individuals mally. In the mutant fly (bottom), that reproduce are diploid and they produce offspring that are also diploid. a mutation causes legs to form in place of the antennae. Some kinds of animals can reproduce both asexually and sexually. For example, (SEMs; magnification 703) a Hydra can clone itself by budding. These species have male and female sexual organs and also reproduce sexually. A few animals have become completely asexual. All whiptail lizards, for example, are females and offspring are clones of the mother. But these animals evolved from sexual species, and their asexual habits are derived characters. Most Animals Have Hox Genes Most animals that scientists have studied so far share a group of genes called homeotic genes. Homeotic (hoh-mee-AH-tihk) genes are a class of genes that control early development. In animals, an important group of homeotic genes called Hox genes are defined by a sequence of 180 nucleotides called homeobox (HOH-mee-uh- bahks) genes. Hox genes define the head-to-tail pattern of development in animal embryos. Homeotic genes create segments in a larva or embryo that develop into specific organs and tissues. The Hox genes within these segments determine the position of cell differen- tiation and development by switching certain genes “on” or “off.” A mutation in a homeotic gene can lead to the development of a body structure in the wrong position. For example, the effect of a mutation in the homeotic gene Antennapedia determines whether an insect body segment will grow antennae or legs. As shown in Figure 1.3, in the wild-type fly (top), antennae develop normally. In a fly with a mutation in this gene (bottom), legs develop where the antennae should be, but the rest of the fly develops normally. The misplaced legs look normal in structure, but are not functional for the fly. Flies with homeotic mutations usually do not live very long. Analyze How are homeotic and Hox genes related? (t), (c) ©F. R. Turner, Indiana University Turner, R. (c) ©F. (t),

Self-check Online HMDScience.com 23.1 Formative Assessment go online Reviewing Main Ideas Critical thinking CONNECT TO 1. In what ways are animals physically 3. Apply How does the structure Genetics diverse? Give three examples. of animal cells allow animals to move? 5. How does the genome of 8c 4. Hypothesize Animals are hetero- an offspring resulting from 2. List and describe the derived trophs. How might this have contrib- sexual reproduction differ characters that all animals share. uted to such great animal diversity? from that of an offspring 7A, 8c resulting from asexual reproduction?

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23.2 Animal Diversity

3f, 7a, 8c Key Concept More than 95 percent of all animal species are invertebrates. VOCABULARY MAIN IDEAS vertebrate Each animal phylum has a unique body plan. invertebrate Animals are grouped using a variety of criteria. phylum A comparison of structure and genetics reveals the evolutionary history of animals. bilateral symmetry radial symmetry protostome Connect to Your World deuterostome When you think of an animal, something familiar such as a dog or a snake probably comes to mind. Both of these animals are vertebrates, a group that represents one 3F research and describe small subset of animals. However, most animals are invertebrates and look nothing the history of biology and like your mental picture. To understand the vast diversity of animal life, biologists contributions of scientists; 7A analyze and evaluate how evidence look for unique characteristics that help them sort animals into distinct groups and of common ancestry among groups arrange those groups into a family tree. is provided by the fossil record, biogeography, and homologies, including anatomical, molecular, and developmental and 8c compare characteristics of taxonomic groups, including archaea, bacteria, protists, MAIN IDEA 7a, 8c fungi, plants, and animals Each animal phylum has a unique body plan. A vertebrate (VUR-tuh-briht) is an animal with an internal segmented CONNECT TO backbone. Vertebrates are the most obvious animals around us, and we are Classification vertebrates too. But vertebrates make up less than five percent of all known Recall from the chapter The Tree animal species. All other animals are invertebrates. Invertebrates (ihn-VUR- of Life that in the Linnaean system of classification, phylum tuh-brihts) are animals without backbones. Early animal classifications divided is the first level below kingdom. all animals into vertebrates and invertebrates. But because invertebrates are not All animals are classified in the defined by a set of shared derived characters, the division is considered out- kingdom Animalia. dated. Many invertebrates are not closely related to one another.

Figure 2.1 Invertebrate Species by Group Animal Phyla Scientists now use shared characters to divide animals into 3% 5% more than 30 major groups. Each group, or phylum (FY-luhm) Arthropods (plural, phyla), of animals is defined by structural and func- 6% Mollusks tional characteristics that are different from every other animal Worms group. Each animal phylum has a unique body plan and represents a different way that a multicellular animal is put together. 86% Sponges, cnidarians, Every animal phylum has a unique set of anatomical charac- echinoderms, and others teristics. These unique characteristics are true of both the largest and smallest phyla. Some phyla, such as mollusks, have tens of thousands of species, ranging from land snails to marine octopuses. Others are much less diverse. Phyla such as Arthropoda contain species that look very different from one another. In other phyla, such as Nematoda, all of the species look very similar. The relative number of invertebrate species per group is shown in Figure 2.1.

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Homeobox Genes and Body Plans If you take a look at the animals that you might see on a walk through a park, you may notice how different their body plans are. The fish swimming in the park’s pond have sets of fins, the birds nesting in the trees have pairs of wings, and the squirrels chasing one another have four legs. Differences in body plans result from differences in the expression of homeobox genes. As shown in Figure 2.2, homeobox genes tell embryonic cells which part of the body they are going to become, such as the head, midsec- tion, or tail. These instructions start a chain reaction that turns on all other genes that define the adult form—where limbs go, how many eyes will develop, the location of the gut, and so on. For this reason, a mutation in a Hox gene can change an animal’s entire body plan. Scientists think that mutations in these genes led to the vast diversity of animal species. All the animal phyla now known first appeared during the Cambrian explosion. How did so many unique body plans appear in such a short time? Biology The trigger may have been an increase in oxygen levels in the atmosphere that HMDScience.com began about 700 million years ago. As oxygen levels rose, eukaryotic organ- GO ONLINE isms could become more active and begin to occupy different niches within Shared Body Structures more complex ecosystems. The Cambrian explosion was possible only because animals had already evolved Hox genes. These genes became a toolkit that changed animal bodies through duplication and loss. For example, a sponge is a simple animal that has at least one Hox gene, while an arthropod has eight. This difference suggests that over time, mutations have caused the original Hox gene to be copied repeatedly, forming a series of similar genes along a chromosome. Every time a gene is duplicated, one of the copies can keep doing its original job in the organism, leaving the other free to mutate and take on new roles. Analyze How are Hox genes related to the diversity of body plans?

FIGURE 2.2 Hox Gene Expression The genes that determine a fruit fly’s body plan are variations of the same genes that determine a human’s, but they are expressed in different patterns.

head tail

fruit fly genes human HOX-B genes

head tail

Analyze In both fruit flies and humans, Hox genes occur in a similar order on chromosomes. How does the illustration emphasize this point?

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sensory organssensory such as eyes. tissue that forms abrain and with region with aconcentration of nervous direction insearch of have food ahead Active hunters that often travel inone usually found on its ventral surface. animal to uses move, such as legs, are Forized. example, structures that an of regions these - can become special (back) and ventral surfaces.Each (belly) which are dorsal bellies, the called animals have also distinctbacks and (head) and posterior ends. (tail) These and tails, which are anterior the called organs found intriploblastic animals. layer,mesoderm and therefore lack complex the they internal tissues and an inner and endoderm animals an do outernot Radial have ectoderm. a Complex organ systems resulted from evolution the of third this tissue layer. is amiddlelayermesoderm that develops into internal tissues and organs. system. is The an endoderm inner layer that lines animal’s the gut. The is outer the derm layer that develops into brain, skin,the the and nervous the tissue. layers These The and ecto- are endoderm, mesoderm. ectoderm, the Bilateral animals are triploblastic, that have is, they three distinctlayers of T each other. Most plans animal into body fall one of of two types symmetry. and two size.ifthe sides An is object are asymmetrical not mirror images of if you draw aline down middleof the asquare, sides both are inshape equal refersSymmetry to how similar an is object across acentral axis. For example, Body symmetry, number of tissue layers, and developmental patterns. characteristics. Three to criteriacategorize used animals are plan body otherLike organisms, animals are placedinseparate groups on certain based • • MAI

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ventral areas. anterior, posterior, dorsal, and its symmetry, thenlabel its animal inyour notes. Mark Draw asimple sketch ofan T • • • • names oftissue layers. can helpyou remember the The following Greek word parts VOCABULARY Chapter 23:Invertebrate Diversity AKI meso- means “middle” endo- means “inner” ecto- means “outer” meaning “skin” -derm comes fr R R E E N ADI ADI G N O N N TE G G S TOOLB TOOLB om aword o o x x

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Biology HMDScience.com Developmental Patterns GO ONLINE Animals are separated into two major divisions: the protostomes and the Digestive Tract Formation deuterostomes. As shown in Figure 2.3, protostome and deuterostome development differs in a number of ways: • First opening of the digestive cavity The major difference between figure 2.3 Developmental patternS protostomes and deuterostomes is the structure that develops from Protostome deuterostome the first opening of the digestive cavity. In protostomes (PROH- 2-cell tuh-stohmz), the mouth is formed first, and the anus second. In deuterostomes (DOO-tuh-roh-stohmz), the first opening forms the anus, and the mouth is formed second. • Gut cavity formation In protostomes, the gut cavity is formed from separations in the mesoderm. In deuterostomes, the gut 8-cell cleavage pattern cavity forms from pouches created by the folds in the gut tube. • Cleavage pattern In most protostomes, early cell divisions lead to an eight-celled embryo in a twisted arrangement called spiral cleavage. In deuterostomes, cells divide into eight-celled embryos spiral radial with cells that are lined up one atop the other in an arrangement Blastula called radial cleavage. Connect Is the symmetry of the human body bilateral or radial?

MAIN IDEA 3f, 7a Blastula cross section A comparison of structure and genetics reveals the evolutionary history of animals. Work by the American zoologist Libbie Hyman in the mid-1900s Gut cavity formation provided the basis for scientists’ understanding of the relationships among invertebrate species. Hyman based her phylogeny, or evolu- ectoderm tionary history, on major events in development. The ability to mesoderm compare ribosomal DNA and Hox genes has helped to both confirm endoderm and rearrange some relationships among invertebrate animal groups. blastopore The presence of tissues is one characteristic that separates one animal group from another. Sponges, which lack tissues, are the First opening of digestive cavity simplest members of the animal kingdom, followed by animals with anus mouth two tissue layers, such as jellyfish and corals. Whether an animal has radial or bilateral symmetry is another defining characteristic. As shown in Figure 2.4, the two major radiations, or phylogenetic branches, are the protostomes and the deuterostomes. Protostomes Protostomes are further divided into the Lophotro- chozoa (flatworms, annelids, and mollusks) and Ecdysozoa (round- blastopore blastopore worms and arthropods). All members of the Lophotrochozoa have becomes mouth becomes anus either a specialized feeding structure made of hollow tentacles or a Contrast How does the development of free-swimming ciliated larval form. Members of the Ecdysozoa must protostomes and deuterstomes differ? shed their outer skin to grow. Deuterostomes Deuterostomes include members of the Echinodermata (such as sea stars and sand dollars) and the Chordata (such as birds, mammals, and all other vertebrates). As a member of the Chordata, you are a deuterostome.

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FIGURE 2.4 phylogeny of Animals

Comparisons of genetic sequences were used to modify the phylogenetic tree of animals.

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radial symmetry bilateral symmetry Animals with radial symmetry Animals with bilateral symmetry have body parts arranged in a can be divided equally only circle around a central axis. along one plane, which splits an animal into mirror-image sides.

NO tissues tissues Tissues are groups of cells that work together to perform a similar function. All animals besides sponges have tissues.

CRITICAL Which phylum is most closely related to humans, who belong to VIEWING phylum Chordata? 8c

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©Carlos Villoch 2004/Image Quest Marine meaning “to move.” comes from aLatin word of sessile ismobile. Mobile meaning “to sit.” Theopposite Sessile comes from a Latin word VOCABULARY cavity gastrovascular nematocyst mesoglea medusa polyp feeder filter sessile VOCABULARY animals bacteria, protists, fungi,plants, and taxonomic groups, including archaea, 8c compare characteristics of molecular, anddevelopmental; homologies, includinganatomical, fossil record, biogeography, and among groups isprovided by the how evidenc F exist today. the simplest anima IGURE R E I D A 7 3.1 A 23.3 analyze andevaluate

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Sponges and cnidarians are the simplest animals. animals. simplest the are cnidarians and Sponges meaning are they unable to move from where are they attached. shows, sponges attach to hard secrete surfaces. They toxic 7a

Chapter 23:Invertebrate Diversity

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Some sponges reproduce asexually by budding. Buds break off from the adult sponge and float in the water until they attach to an underwater surface, where they grow into their adult form.

Sponge Anatomy CONNECT TO Sponges do not have mouths. As you can see in Figure 3.2, their cells are Symbiosis arranged around a network of channels that let water flow directly through the Recall from Interactions in sponge’s body. Water is pulled into the sponge through tiny pores in its body Ecosystems that symbiosis is a wall, and used water is ejected from a larger hole at the top of the sponge close relationship between two called the osculum. Of the thousands of known species of sponges, most are or more species living in close marine filter feeders. Filter feeders eat by straining particles from the water. contact. Sponges form symbiotic relationships with many different Sponges can be found in many colors and shapes. Some sponges are shaped animals. Shrimps, crabs, and like tubes, while others lie flat against the ocean floor. Regardless of their worms have been found living shape, all sponge bodies are made up of two layers of cells that cover a frame- within the cavities of a sponge. work of collagen-like fibers, called spongin. The skeleton is usually reinforced with hard calcium- or silicon-based crystals called spicules. While sponges do not have tissues, they do have several types of specialized cells. • Pinacocytes These thin and leathery cells form the sponge’s outer layer. Biology IDEO • Choanocytes These cells, also called “collar cells,” form the inner layer of V CL IP the sponge. Each has a long flagellum surrounded by a collar of tiny HMDScience.com hairlike structures called microvilli. These cells pull water through the GO ONLINE sponge by beating their flagella. As the water passes the choanocytes, tiny Sponges food particles are trapped in the mucus on the microvilli. • Amoebocytes These are mobile cells found in the jellylike material sand- wiched between the two cell layers. Amoebocytes absorb and digest the food particles caught by the choanocytes and move the nutrients to other parts of the sponge. They also transport oxygen and wastes in the sponge. Because of their mobility, amoebocytes are important to a sponge’s growth and repair of injuries. Summarize What characteristics make sponges the simplest animals?

FIGURE 3.2 Sponges are animals that have specialized cells but lack tissues. This cutaway spicule shows the internal organization of a sponge. osculum pore

pinacocyte

choanocyte amoebocyte

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(t) ©Jeff Rotman/Nature Picture Library; (b) ©Phillip Colla/www.OceanLight.com have specialized tissues. are oldestCnidarians the existing that animals

the nematocyst.the A oftypes cells. TheGLEE-uh). outer layer of tissue is made up of three ians such as corals. tacles facing upward. This form is characteristic of cnidar- (PAHL-ihps) tubes with aremouth and cylindrical ten- noncellular material jellylike called haveCnidarian bodies two tissue layers separated by a AnatomyCnidarian planula develops then into polyp the stage. develops aplanula. into called The afree-swimming larva, by releasing gametes into water. the egg The fertilized spring. In medusa the form, cnidarians reproduce sexually ding. produces This method genetically identical off- during its life cycle. Polyps reproduce by asexually bud- A cnidarian may reproduce and asexually sexually both Reproduction Cnidarian medusa, of both which are shown in Cnidarians have forms: two body polyp the and the CharacteristicsCnidarian ate movements using simple and muscles. nerves pulsing through water the and an anemone waving its tentacles make deliber- In contrast to sponges, cnidarians (ny-DAIR-ee-uhnz) can move. Ajellyfish have symmetry, radial acharacteristic of cnidarians. all forms during polyps life their and cycle. Both medusas Manyfish. cnidarian alternate species two the between characteristic of free-swimming cnidarians such as jelly- mouththeir and tentacles on underside. the This form is a thin, coiled,a thin, harpoon-shaped tubule with apoisonous barb at one end. Nerve • Contracting • Cnidocytes • MAI One t of are them on tentacles. the to cnidarians. are Cnidocytes found over all acnidarian’s body, but most stinging for structures used defense and capturing prey. are They unique of cnidarian the and contain muscle fibers. muscular contractions. Cnidarians do not have brains. informationanimal. sensory send They around animal the and coordinate N ID ype ofype stinging structure found anemones sea inboth and is jellyfish

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(NY-du Ner cel ls nematocyst ve cells interconnect and form anetwork over entire the Medusas

8c Con h-syts) tracting cells covertracting surface the are umbrella-shaped, with

(NEHM-uh-tuh-sihst) is acapsule containing Cnid mesoglea ocytes are specialized cells that are containocytes specialized Figure 3.3. 3.3. Figure (mehz-uh- P olyps

F mouth face downward. (bottom), thetentacles and formthe medusa ofajellyfish and mouth face upward. In of IGURE a coral (top), the tentacles Chapter 23:Invertebrate Diversity 3.3

In thepolyp form

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Nematocysts, shown in Figure 3.4, usually do not fire on contact unless a gastrovascular cavity mouth chemical signals the presence of prey or a predator. When they fire, nemato- mesoglea cysts uncoil rapidly to spear and poison prey. Prey captured by nematocysts on their tentacles are stuffed through the animal’s mouth into a saclike digestive space called the gastrovascular cavity. The cavity is lined with the cnidarian’s inner tissue layer, which has cells that secrete digestive enzymes and absorb nutrients. Cnidarians do not have an anus, which in other animals is a separate exit for wastes. In cnidarians, wastes are pushed out through the mouth. The gastrovascular cavity also moves oxygenated water to internal cells. When the animal’s mouth is closed, water in the cavity becomes pressurized and provides skeletal support to the tissue, similar to a balloon full of water. Muscular contractions can work against the pressurized fluid and change the tentacle animal’s shape. oral arms Cnidarian Classes There are four major groups, or classes, of cnidarians. Each class is defined in part by which body form is dominant during the animals’ lives. • Anthozoa Nematocyst Structure (an-thuh-ZOH-uh) include sea anemones and corals. The polyp form is dominant in these animals. There is no medusa stage. discharged • Hydrozoa (hy-druh-ZOH-uh) include fire corals, the Portuguese nematocyst man-of-war, and hydras. These animals alternate between polyp and barbs medusa forms. Medusas reproduce sexually, producing gametes that coiled nematocyst fuse to produce larvae. Larvae settle to the sea floor and grow into polyps. Most polyps are asexual. • Scyphozoa (sy-fuh-ZOH-uh) are jellyfish. The medusa form is dominant in these animals. Some species have either a very short polyp stage or none at all. • Cubozoa (kyoo-buh-ZOH-uh) include the tropical box jellyfish and sea wasps. These animals also have a dominant medusa form. Unlike Scyphozoa, they have a cube-shaped body and well-developed eyes with FIGURE 3.4 Cnidarians such as retinas, corneas, and lenses—though how an animal with no brain this jellyfish use nematocysts, a interprets visual data is still unknown. type of stinging structure found on their tentacles, to both cap- Contrast How do the polyp and medusa forms differ? ture prey and defend themselves against predators. Self-check Online HMDScience.com GO ONLINE

23.3 Formative Assessment CONNECT TO Reviewing Main Ideas Critical thinking Evolution 1. What is the main function of each of 3. Infer What are the advantages of a 5. Some sponges have the the three types of cells that make up gastrovascular cavity to the body remarkable ability to reas- a sponge’s body? functions of a cnidarian? semble themselves after they are experimentally broken 2. What are the functions of the inner 4. Contrast How do sponges and down into individual cells. and outer tissue layers in a cnidarian? cnidarians defend themselves against What might this suggest predators? What is different about about the origin of multicel- the methods used by each? 8c lularity in animals?

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Creepy Crawlies

Biology VIDEO C BIOZINE BIOLOGY LIP The Loss of Biodiversity Shared Body Structures Echinoderms Explore how Fascinating discoveries about Animals that look very different can variations of the sea star’s invertebrates are often in the have similar body structures. Compare five-part body plan form headlines. Catch the latest structures and organs of four different other echinoderms. news about invertebrates and invertebrates to explore shared other animals in the BioZine. characteristics. (bl) ©blickwinkel/Alamy

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23.4 Flatworms, Mollusks, and Annelids

8c Key Concept Flatworms, mollusks, and annelids belong to closely related phyla. VOCABULARY MAIN IDEAS complete digestive tract Flatworms are simple bilateral animals. radula Mollusks are diverse animals. hemocoel Annelids have segmented bodies. segmentation coelom Connect to Your World Imagine if you had no stomach or lungs. Just like a flatworm, you would have to be 8c compare characteristics of taxonomic groups, including rather flat and thin in order to get the oxygen and food you need to survive. While archaea, bacteria, protists, fungi, some flatworms can grow up to 20 meters long, they are never more than a few plants, and animals millimeters thick.

MAIN IDEA Flatworms are simple bilateral animals. Based on molecular studies, most flatworms, mollusks, and annelids are classified together as members of the Lophotrochozoa. These animals have either a feeding structure made of hollow tentacles called a lophophore, or a distinctive free-swimming ciliated larva called a trochophore. The name Lophotrochozoa is taken from these two anatomical features. Flatworms have a solid body and an incomplete or absent gut. A flatworm’s shape is the direct result of having no circulatory system. Flatworms can move oxygen to their cells only by diffusion, so all their cells must be close to the FIGURE 4.1 Planarians, such as this zebra flatworm, have a solid outside environment. Complex derived characters such as gut tubes were body that lacks a complete gut. probably lost at a later stage of evolution, often as the flatworms became parasitic on other animals. The three classes of flatworms include planarians, reproductive flukes, and tapeworms. head eyespot system Planarians Planarians are free-living, nonparasitic flatworms. Planarian worms have a head with eyespots and a simple brain built of a cluster of nerve tissue. As shown in FIGURE 4.1, the mouth is found on the animal’s ventral surface rather than in its head, and it leads to a gut cavity. A muscular tube called the pharynx extends from the mouth to collect food. These pharynx worms actively hunt for food using chemoreceptors to detect odors in the water or in the air. They mouth usually move using the cilia on their ventral sucker surface, but they also have bands of muscle that let them twist their bodies. gut cavity

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FIGURE 4.2 Life Cycle of a Parasitic Fluke The fluke Schistosoma can infect humans and cause a serious disease called schistosomiasis.

Adult fluke The larva eventually settles in the human intestine, where it matures into an adult. (LM; magnification 403)

Human The fluke larva penetrates through Snail After hatching from eggs in Egg An egg is passed in human feces a human’s bare skin into the blood vessels. the water, the young flukes infect back into local waters. (LM; magnifica- their intermediate host, an aquatic tion 4003) snail. Inside the snail, the flukes develop into tadpolelike larvae. Flukes Flukes are parasites that feed on the body fluids of other animals. Flukes have a mouth with a pharynx that opens into a gut cavity. They are found in both invertebrate and vertebrate hosts. Many species of flukes have life cycles that involve more than one host. Figure 4.2 shows the life cycle of one fluke, Schistosoma (shihs-tuh-SOHM-uh), which can infect humans and cause a serious disease called schistosomiasis. This disease affects about 200 million Web people in areas such as Africa and Southeast Asia. The disease is contracted HMDScience.com by wading in or drinking fresh water contaminated with fluke larvae. Symp- GO ONLINE toms of the disease include the onset of fever and muscle pain within one to Parasites two months of infection. The disease is treated by an antiparasitic medicine. Tapeworms Tapeworms are parasites that live in vertebrate guts. They have a small head CONNECT TO with suckers or hooks used to attach to the host. Their long, ribbonlike body Structure and has no gut. Instead of swallowing food, these animals absorb nutrients from Function the digested food in which they live. An adult tapeworm’s body is made up of The simple structure of a tape- segments containing both male and female sexual organs. When these segments worm reflects that as an adult it does not have to move or digest fill with fertilized eggs, they break off and are excreted with the host’s feces. food. The lack of complex inter- Many tapeworms have complex life cycles involving multiple hosts. The nal systems allows for a simpler life cycle of a dog tapeworm begins when an egg is passed with a dog’s feces. body plan. A flea eats the egg, and the egg develops into a larva within the flea’s body. The tapeworm infects another dog when it accidentally eats the infected flea while licking its fur. The tapeworm develops into an adult within the dog’s intestines, and the cycle begins again. Contrast How are planarians different from flukes and tapeworms? (tl) ©Alan Towse; Ecoscene/Corbis; (tr) (tl) Towse; ©David©Alan Scharf/Science Faction/Getty Images; (tc) Inc./Alamy Arnold, Images; ©Peter (r) ©John Durham/Photo Inc. Researchers,

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MAIN IDEA 8c Mollusks are diverse animals. While flatworms have a digestive sac with only one opening, mollusks and all other bilateral animals have a complete digestive tract. A complete digestive tract consists of two openings—a mouth and an anus—at opposite ends of a continuous tube. Because food moves one way through the gut, animals with complete digestive tracts can turn their guts into disassembly lines for food. As food moves down the gut, it travels through areas that are specialized for digestion or absorption. Animals with complete digestive tracts can eat con- tinuously. This efficient and frequent digestion allows animals to be more active. Mollusk Anatomy Biology IDEO V CL Mollusks include animals as different-looking as oysters, garden snails, and IP giant squid. Mollusks may be sessile filter feeders, herbivores that graze on HMDScience.com algae, or predators. Despite this variety of form and lifestyle, all mollusks share GO ONLINE at least one of three features, shown in FIGURE 4.3. Mollusks • Radula The radula is a filelike feeding organ. Mollusks eat by scraping the radula over their food. The hard teeth of the radula pick up tiny particles that the animal swallows. • Mantle The mantle is an area of tissue covering the internal organs. In most mollusks, the mantle secretes a hard, calcium-based shell that pro- tects the animal from predators. • Ctenidia (tih-NIHD-ee-uh) The ctenidia are flat gills found in a pocket of the mantle tissue called the mantle cavity. The gills absorb oxygen from water that enters this cavity. In the land-dwelling snail shown below, the gills have been lost, and oxygen is absorbed from air rather than from water in the cavity. While the gills contain blood vessels, blood is also pumped through the hemocoel. The hemocoel (HEE-muh-seel) consists of spaces between cells within the animal’s tissues. This circulatory system extends into a large muscular foot. Snails and slugs crawl on the foot, while clams and scallops dig with the foot. In cephalopods, such as squids and octopuses, the foot forms a muscular siphon, parts of the tentacles, and head.

intestine heart

stomach mantle cavity

mantle digestive gland

FIGURE 4.3 The anatomy of a common garden snail includes a radula and a mantle, both of which are features shared by mouth most mollusks. foot salivary gland crop radula anus

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©Brian J. Skerry/National Geographic Image Collection Summarize weeks, juvenile snails hatch from eggs. the are eggs These eggs. laid inunderground of nests. two to After aperiod four ferred into recipient the snail. This packet the to of fertilize is used sperm tive system to store more mating, During sperm. apacket of is trans- sperm This calcium-rich, mucus-covered causes dart recipient the snail’s reproduc- Just before mating, impregnating the snail fires a“love dart” into other. the female reproductive organs. Reproduction usually involves cross-fertilization. are hermaphrodites. Hermaphrodites are organisms that have and male both Mollusks avariety of use reproductive strategies. Garden snails, for example, Reproduction Mollusk gastropods, pelecypods (bivalves), and cephalopods. species, however, are found within three classes: the There are seven classes of mollusks. The majority of Classes Mollusks of • • • • • • •

Pol Sca Try Apl Cep Pel Gas scrape algae and plant matter from the rocks. their lifetime clinging to rocks, where feed bythey using their radula to have a shell with overlapping plates. These marine mollusks spend most of at bottom the of water whereon feed they detritus. bodies, shellstheir resemble shape the of an elephant’s tusks. mollusks These live that live water. indeep were rediscovered in1952.Little is known about marine these mollusks on marine small invertebrates, others while are parasites of coral. mollusks, do not have shells. mollusks These live water. indeep Some feed crustaceans, and fish, other mollusks. well-developed. are Cephalopods carnivores that eat animals such as mollusks, system nervous the and eyeof are cephalopod the most the shown in in marine ecosystems. together. Most bivalves are filter feeders that live protected by two hard shells that are hinged bivalves, called also have that body asoft is mussels, and Pelecypods, which are scallops. that are herbivores, carnivores, and scavengers. aquatic ecosystems. This class includes species Mollusk phylum. live They land inboth and make up over of half found species the inthe branchs, abalones, and limpets. Gastropods ecypoda yplacophora blidiiae phopoda acophora tropoda halopoda

Wha F

igure t common features are shared by mollusks? by mollusks? shared are features t common

Thi

Thi Thi

Thi Thi Thi s class of mollusks but was once extinct, to be believed they

4.4, s class includes clams, oysters, s class includes snails, nudi- Thi s class is also called the tusk the s class shells, called named is so also because s class includes wormlike small animals that, most unlike s class includes squid, as octopuses, nautiluses, and cuttlefish. Among the s class the chitons, is called also which are animals that 8c meters (6 inlength. ft) jumbo, s FIGURE 4.4 FIGURE structures inunrelated species. tion istheevolution ofsimilar lations that convergent evolu- from TheEvolution ofPopu- occurred independently. Recall cephalapod andhumaneyes However, theevolution of of alens, retina, iris,andpupil. cephalopod eye ismade up Much like thehumaneye, the Evo C o Chapter CO n lu NNE v quid may grow to nearly 2 e t

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T Invertebrate Diversity

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QUICKLAB observing Anatomy of a Clam A clam is a bivalve mollusk. In this lab, you will explore the parts and systems of a clam.

Problem What are the internal organs and systems of a clam? Materials Procedure • preserved clam specimen 1. Place the clam in the dissecting tray and follow the instructions on • dissecting tray the drawing to carefully open the shell. • Anatomical Clam Drawing 2. Look for the gills, and use your probe to study them. • screwdriver 3. Observe and note the shape of the foot. Locate the palps. • scalpel • probe 4. Follow the instructions to peel away the muscle layer to see the • scissors internal organs. • forceps 5. Locate the reproductive organs, and then find the digestive system. • 12 dissecting pins 6. Dispose of your specimen as instructed by your teacher. • hand lens • paper towels Analyze and Conclude 1. Infer What organ does the clam use to breathe? 2. Infer The clam is a filter feeder. Based on your observations of the digestive system, how does the clam eat? 3. Infer The arteries and veins are not attached to each other. How might the circulatory system work?

MAIN IDEA 8c Annelids have segmented bodies. All annelids share more similarities in their body plans than mollusks do. Three groups of annelids—earthworms, marine worms, and leeches—are characterized by segmentation. Segmentation refers to the division of an organism’s body, in this case an annelid’s long body, into repeated sections that contain a complex set of body structures. Annelid Anatomy The features of an annelid’s segmented body are shown in FIGURE 4.5. A typical annelid segment contains part of the digestive tract, nerve cord, and blood vessels that carry blood to the worm’s tissues. Annelids have a closed circulatory system, where blood travels in a closed circuit inside blood vessels. Each body segment also contains organs that collect and excrete wastes, bands of longitudinal and circular muscle, and a coelom. R E ADI n g TOO LB ox The coelom (SEE-luhm) is a fluid-filled space that is completely sur- VOCABULARY rounded by muscle. The coelom is divided by partitions called septa (singular, Coelom comes from a Greek septum). The fluid inside the coelom acts as a hydrostatic skeleton. To under- word meaning “cavity.” Septum comes from a Latin word stand how a hydrostatic skeleton works, think of a water balloon. When you meaning “partition.” squeeze one end, the water moves to the opposite end. An annelid uses its hydrostatic skeleton in a similar way to move from one place to another. When the longitudinal muscles contract, the segment shortens. When circular muscles contract, the segment lengthens. Alternating waves of contractions move from head to tail, producing the worm’s characteristic crawling motion.

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FIGURE 4.5 Annelids, such as earthworms, have similar body plans, characterized by segmentation.

brain muscle hearts

blood vessels

mouth digestive tract

segment nerve cord Biology VIDEO C Annelid Diet LIP Earthworms and marine worms eat organic waste material. Earthworms HMDScience.com excrete digested material, called castings, into the soil. Castings help maintain GO ONLINE a nutrient-rich soil. While most people think of leeches as blood-feeders, a Annelids number of leech species are actually predators that feed on invertebrates such as snails and aquatic insect larvae. Annelid Reproduction Annelid reproduction may be either asexual or sexual. Asexual reproduction results from fragmentation. In this method, a portion of the posterior end of the annelid breaks off and forms a new individual. Some annelids, such as earthworms, are hermaphrodites. Just as in land snails, reproduction occurs by cross-fertilization. Other annelids, such as marine worms, have separate males and females. Fertilized eggs of marine annelids initially develop into free- swimming larvae. Larvae grow in size by the formation of new segments. Contrast In what ways are annelids different from mollusks? 8c

Self-check Online HMDScience.com 23.4 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO Evolution 1. Describe the characteristics that 4. Apply How might a community separate the three groups of flat- prevent Schistosoma infections? 6. Free-living flatworms have worms. 8c 5. Infer What adaptations might pairs of sensory organs in their heads. What might 2. What is the function of a mollusk’s mollusks without shells use to defend make two sense organs set radula? against predators? on either side of the head 3. What are the three groups of anne- more adaptive than a single lids? Describe their body plan, using central organ? the word coelom. 8c

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23.5 Roundworms

Key Concept VOCABULARY Roundworms have bilateral symmetry and shed cuticle their outer skeleton to grow. pseudocoelom MAIN IDEAS Roundworms shed their stiff outer skeleton as they grow. Many roundworms are parasites.

Connect to Your World Imagine grabbing a handful of soil. In that single handful, there may be thousands of roundworms. These animals are found in nearly every ecosystem on Earth, including mountaintops and deep ocean trenches. They are also found within extreme envi- ronments such as hot springs and Arctic ice.

MAIN IDEA Roundworms shed their stiff outer skeleton as they grow. Roundworms, also called nematodes, are one of the most numerous kinds of animals, in terms both of numbers and of species diversity. The more than 15,000 species of roundworms vary in size from less than a millimeter to over 10 meters in length. Roundworms are part of the group Ecdysozoa, which also includes arthropods—crustaceans, spiders, and insects. Like mollusks and annelids, members of the Ecdysozoa are protostomes and have bilateral symmetry. All Ecdysozoans have a tough exoskeleton called a cuticle. The cuticle (KYOO- FIGURE 5.1 Roundworms have a tih-kuhl) is made of chitin, and must be shed whenever the animal grows cylindrical shape and must shed their tough outer cuticle to grow larger. When the animal sheds its cuticle, its soft body is exposed to predators in size. until its new skeleton hardens. tail Roundworm Anatomy As shown in Figure 5.1, a roundworm is cylindrical, with a blunt head and tapered tail. It is covered with a tough cuticle that lies anus over a layer of muscle. Muscle in the roundworm is laid out ovary lengthwise. This arrangement means that a roundworm moves by bending its body side-to-side. Rather than crawling like other intestine types of worms, a roundworm’s movement is more whiplike. Muscle within the roundworm is separated from the central gut tube by a fluid-filled space. This fluid-filled space is called a pseudocoelom (soo-duh-SEE-luhm) because it is not completely lined by muscle. (The prefix pseudo- means “false.”) Roundworms mouth do not have circulatory or respiratory systems. However, they nerve ring pharynx (brain) do have a digestive system, which includes a mouth, pharynx, cuticle intestine, and anus. Food that is eaten, such as plant matter, algae, or bacteria, travels the length of the roundworm, from the mouth at one end to the anus at the other.

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Roundworm Reproduction Most roundworms reproduce sexually. In some cases, female roundworms bear live young after eggs hatch within the female’s reproductive tract. In most cases, however, larvae develop from eggs laid by the female. Round- worms grow into their adult form by molting. Contrast How does growth differ in a roundworm and in a human?

MAIN IDEA Many roundworms are parasites. Roundworms are parasites of nearly every plant and animal species. These animals cause a lot of damage to the crop species they infect. Such a wide- spread loss of crops can seriously harm the economy of farming communities. Other roundworms infect humans. These roundworms include hookworms, pinworms, and guinea worms. • Hookworms A hookworm is found within the digestive tract of its host. This parasite feeds on its host’s blood. A hookworm infects its human host when a person walks barefoot over contaminated soil. Over 1 billion people are infected with hookworms. Such infections are common in the tropics and subtropics. • Pinworms A pinworm is found in the gut of its host. Pinworm infections often occur when the host accidentally swallows eggs picked up from contaminated surfaces. • Guinea worms Guinea worms are found in the guts and connective tissues of their hosts. Guinea worm infections occur when a person drinks contaminated water. Work by global health organizations has helped to eliminate this disease from most of the world. Infer Why might most parasitic roundworms live in the gut of their host? ©www.CartoonStock.com

Self-check Online HMDScience.com 23.5 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Why do roundworms molt? Use 3. Contrast How are earthworm and Parasitism the term cuticle in your answer. roundworm body cavities different? 5. Many species of roundworms 2. What are three parasitic roundworms 4. Apply How might Guinea worm are parasites of plants and that infect human hosts? infections be prevented? animals. How is a roundworm’s body plan related to its function as a parasite?

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23.6 Echinoderms

8c Key Concept Echinoderms are on the same evolutionary branch as vertebrates. VOCABULARY MAIN IDEAS ossicle Echinoderms have radial symmetry. water vascular system There are five classes of Echinoderms.

8c compare characteristics Connect to Your World of taxonomic groups, including archaea, bacteria, protists, fungi, If you have ever seen a tide pool, you may have noticed several creatures clinging to plants, and animals the pool’s rocky bottom and sides. Brightly colored sea stars and spiky sea urchins are just two of the echinoderms that are often found in these habitats.

MAIN IDEA Echinoderms have radial symmetry. Adult echinoderms are slow-moving marine animals that have radial symmetry. In contrast, echinoderm larvae have bilateral symmetry. This difference suggests that echinoderms had bilateral ancestors and that radial symmetry is a derived character. Echinoderm Anatomy The anatomy of a sea star is shown in Figure 6.1. Note that each arm of a sea FIGURE 6.1 Echinoderms, such star contains both digestive glands and reproductive glands. For clarity, they as sea stars, are radially symmetri- cal animals with an internal skel- are shown separately in different arms in the illustration. eton made of interlocking plates All echinoderms have an internal skeleton made up of many tiny interlock- embedded under the skin. Three ing calcium-based plates called ossicles. These ossicles are embedded within arms of this sea star have been “cut away” to show internal anat- the skin. The plates are joined together by a unique catch connective tissue omy. with adjustable stiffness. Catch connective tissue allows echinoderms to change their consistency, going from very flexible to very digestive glands stiff in a matter of seconds. The combination of a firm skeleton and a surface covered with spiny projections anus (often poisonous) helps to fend off predators. Echinoderms have a water vascular system, which is a central disk series of water-filled radial canals that extend along each arm from the ring canal surrounding the central disk. The radial canals store water that is used for circulation and for filling tiny suckerlike appendages along the arms called tube feet. Changes in water tube feet pressure extend and retract the tube feet. On its own, a tube foot is small, but many of them working together can exert large radial canal ring canal forces. Tube feet are used to grab objects reproductive glands and to move around.

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(t) ©Alexis Rosenfeld/Photo Researchers, Inc.; (b) ©Fred Bavendam/Minden Pictures T Connect here are five ofEchinoderms. classes

happen to come stars upon. sea are Other carnivorous predators. feeders, meaning eat that will whatever they source food they starsSome sea are filter others feeders, while are opportunistic stars areSea members of class the Asteroidea (as-tuh-ROY-dee-uh). StarsSea NOY-dee-uh). A feather star, shown in Feather stars and sea lilies are members of the class CrinoideaFeather Stars Lilies Sea and (kry- round urchin sea to oblong the and well-named the cucumber. sea Echinoderms have avariety of plans, body ranging from spiny the the echinoderm settles onto the ocean floor, where it develops into an adult. right side forms the ossicle plates that will protect its outer surface. Eventually, adult form. The side left of to itsform begins body the tube the feet, while As it matures, an undergoes echinoderm acomplex of series changes into its developsegg into planktonic afree-floating, that matures larva water. inthe The fusion of gametes these results infertilization ofThe fertilized egg. the and fromsperm eggs reproductive the glands arms intheir into water. the Most echinoderms reproduce sexually. Adult stars, sea for example, release Reproduction Echinoderm or regrow, limbs, their as shown in stomach. Waste material exits out anus. the clam’s body. The clam is completely digested inthe digestive juices from digestive the glands dissolve the narrow two the shells space between of aclam, and stomach out of mouths. their The stomach enters the apart clam’s the stars shell. are Sea able to push their clamthe with its tube feet and pressure uses to pull and an anus. To eat star aclam, grabs hold asea of up o a portion of a sea star’sa portion of asea central disk, must remain. still For regeneration to occur, such parts, as body certain disturbed. when system, sometimes which eject they cancucumbers regenerate aportion of digestive their their arms to collect and transfer food to the mouth. These animals filter feed by using the tube foot–like extensionsattached covering to the ocean bottom by a stalk on one side of theirarms, bodies. but it is usually attached to a surface. Sea lilies are sessile. They are MAI Ech star hasA sea acomplete digestive system made f amouth, stomach, length asmall of intestine, N

ID inoderms suchinoderms stars as sea can regenerate, A seahas bilateral star symmetry. specimen Is it an adult or a larva? Why? EA

8c Figure 6.2. Figure Figure 6.3, Sea Sea can move with its These animals are filter feeders. members oftheclas F F ate, orregrow, limbs. echinoderms are abl IGURE IGURE Chapter 6.2 6.3

23: Feather stars are Sea stars andother

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FIGURE 6.4 Basket stars (left) Brittle Stars and Basket Stars use their long, branched arms to Brittle stars and basket stars are both members of the class Ophiuroidea capture plankton. Sea urchins (middle) are covered in long, sharp (ahf-ee-yuh-ROY-dee-uh). Brittle stars have long spindly arms and are fast spines that protect them from movers. Because their tube feet lack suckers, brittle stars use their arms to predators. Sea cucumbers (right) move. Some brittle stars are scavengers that feed on detritus on the ocean are fleshy animals that live on the ocean floor. floor. Others are predators. Basket stars, shown in Figure 6.4, also have long arms, although with many branches. Basket stars filter feed by capturing plankton with their arms. Sea Urchins, Sea Biscuits, and Sand Dollars Sea urchins, sea biscuits, and sand dollars are all members of the class Echi- noidea (ehk-uh-NOY-dee-uh). The bodies of sea biscuits and sand dollars are covered with tiny projections, which the animals use for movement and for burrowing on the ocean floor. Sea urchins, which do not burrow, do not have these projections. Instead, these animals are covered in long, sharp spines. Burrowing animals feed on waste matter on the ocean floor. Most sea urchins graze on algae by trapping it on sticky tentacles found on their ventral side. Sea Cucumbers Biology IDEO Sea cucumbers are the only members of the class Holothuroidea (hahl-uh- V CL IP thu-ROY-dee-uh). Sea cucumbers are fleshy animals that have a long, bilateral HMDScience.com shape. Instead of arms, sea cucumbers have thick, fleshy tentacles. These GO ONLINE tentacles are used to capture particles of food, which the animal eats by pulling Echinoderms its tentacles through its mouth. Sea cucumbers, which live on the ocean floor, are also sediment feeders. These animals absorb food items in their digestive tract, and eject nonfood particles through their anus.

Contrast How do feeding behaviors differ between sea stars and sea cucumbers? Center/South (tl) Carolina ©Southeastern Department Taxonomic Regional of Natural Resources; (tc) ©Flip Nicklin/Minden Pictures; (tr) ©Fred Bavendam/Minden Pictures 8c Self-check Online HMDScience.com 23.6 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. How does the water vascular system 3. Contrast How do the feeding habits Bioindicators enable echinoderms to move? of sessile echinoderms differ from 5. Sea urchins live on rock- and 2. Describe the differences in body those that are mobile? sand-covered areas of the plans between the five classes of 4. Infer How does an echinoderm ocean floor. What changes in echinoderms. 8c benefit from the ability to regenerate an ocean ecosystem might limbs? be indicated by an increase in the sea urchin population?

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CHAPTER 23 G N I D A E R

the definitionofterm. below, explain how themeaning oftheroot relates to Using theGreek orLatin word originsoftheterms picture, andwrite caption. ashort lines, orarrows to illustrate Labeleach themeaning. F V R 23.2 23.1 vo Chapter 10. 12. 13. 11. or each word orword pairbelow, use simple shapes, 8. 6. 4. 2. 5. 9. 3. isualize 7. 1. eviewing

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escape from predators? How t doestheability system? What ofanechinoderm isthefunction health. hosts. Name oneandexplain how itaffects human Sever Why mustroundworms shedtheirout Describe what as phylum includesanimals withsegmented bodies? Mollusks havMollusks benefit ofhaving thisfeature? main features ofeach. What are thethr which includejellyfish andcorals. Describe thetwo g the animal king What four characteristics are common to members of What characteristic makes sponges thesimplest animals? ev What typesofevidence are used to puttogether the into gr Describe three different criteria used to classify animals ver What isthedifference between aninvertebrate anda olutionary history oftheanimal kingdom? tebrate? al speciesofroundworms are parasites with human HMDScience.com Interact oups.

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697 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Critical Thinking 27. Analyze How are the functions of Hox genes related to Analyzing Data Analyze a Scatterplot the diversity of body plans and characteristics within the Scientists measured the depth and velocity of water in animal kingdom? 8c the Columbia River in Washington. These data are shown 28. Contrast How is development different between an on the scatterplot graph below. Use the graph to answer echinoderm and a mollusk? Use a table to summarize the next three questions. their different development patterns. Columbia River Depth and Velocity 29. Infer While both sponges and cnidarians are simple 1.6 animals, cnidarians have specialized tissues. What might be some advantages of having specialized tissues? 1.2

30. Infer Why is the ability to secrete toxic substances 0.8 important to the survival of a sponge? 0.4 31. Synthesize How has molecular biology played a critical (ft/sec) Velocity 0.0 role in our understanding of animal relationships and 0 3 6 9 12 phylogeny? 7c Depth (ft) 32. Infer Even when an annelid is cut in half, it can often still survive. What anatomical feature enables an annelid Source: USGS to remain alive when half of its body is gone? 37. Analyze What type of relationship exists between the depth and the velocity of the water? Explain your 33. Apply What is the function of an echinoderm’s catch answer. connective tissue? 38. Predict Make a prediction about the velocity of the 34. Compare and Contrast Animals exhibit variety in their water if the depth were 14 feet. digestive systems. What do you think are the advantages and disadvantages of having a gastrovascular cavity 39. Infer In what way might a species adapted to living compared with a complete digestive tract? 8c at lower depths differ from a species adapted to living in shallow water? Interpreting Visuals Use the Hox gene diagram below to answer the next two questions. Making Connections 40. Write a Travel Brochure Imagine you are an advertis- head tail ing director for a travel agency. Choose an invertebrate from this chapter, and create a brochure to entice your chosen invertebrate to visit a vacation spot. Remember that each invertebrate species has specific requirements fruit fly genes for survival. In your brochure, include a description of the location (and why it is the perfect place for your invertebrate), the menu from a local restaurant, and other features that would make your chosen inverte- human HOX-B genes brate feel at home. 41. Connect In addition to storing poisonous chemicals from their food, nudibranchs also are very colorful. In head tail other colorful animals, such as birds, fish, and insects, colors are important for a variety of reasons. What might be the adaptive advantage of a nudibranch’s bright coloration? 35. Apply How do the two organisms above display the pattern seen in all Hox genes? 36. Synthesize How does the diagram support the idea that all animals share a common ancestor? 7a

698 Unit 8: Animals Biology End-of-Course Exam Practice

Record your answers on a separate piece of paper. 2G, 7A MULTIPLE CHOICE 4 Appearance of Early Animals in Fossil Record 2C, 3F, 8A Organism Type Appearance in Fossil Record 1 The earliest classification system divided all Sponges 570 million years ago animals into two main groups. Linnaeus’s original Mollusks 545 million years ago classification scheme used six major groups of animals. Now, based on hundreds of years of Echinoderms 500 million years ago scientific research, over 30 animal groups, or phyla, are recognized. This progression supports Choanoflagellates are animal-like protists that do the idea that scientific evidence — not leave behind fossil evidence. They are A changes frequently considered the most likely ancestors to sponges and all other animals. Based on the table above, B should be disregarded after 100 years when did choanoflagellates likely evolve? C is cumulative A less than 500 million years ago D is often incorrect B between 545 and 500 million years ago 6D C between 570 and 545 million years ago 2 D more than 570 million years ago

6E, 7F 5 Which of the following statements best describes the impact that Hox genes have on animal diversity? A Mutations in Hox genes lead to greater animal The illustration above shows the chromosomes diversity. within the egg cell of a snail. If this egg cell unites with a sperm cell of the same snail species, the B Mutations in Hox genes lead to decreases in offspring will have — animal diversity. A 6 chromosomes from each parent C Mutations in Hox genes lead to less variability in animal body plans. B 6 pairs of chromosomes from each parent D Mutations in Hox genes prevent species from C 12 chromosomes from each parent occupying new niches when environmental D 12 pairs of chromosomes from each parent conditions changed. THINK THROUGH THE QUESTION 8C Recall that each egg and sperm cell has a single set of chromosomes. 6 Which of the following provides the best evidence that animals and fungi evolved into multicellular organisms independently? 6G A They are both heterotrophic organisms. 3 Two roundworms mate and produce offspring. B Animals have eukaryotic cells and fungi have Which of the following most directly accounts for prokaryotic cells. each offspring receiving half of its DNA from C Fungal cells do not have the same functions as each parent? animal cells. A mutation D Fungi are autotrophic organisms and animals B maturation are heterotrophic organisms. C mitosis D meiosis

Chapter 23: Invertebrate Diversity 699