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GUIDE FOR READING 29-1 Echinoderms After you read the following sections, you will be able to CHAPTER Guide For Reading What are echinoderms? 29-1 Echinoderms • Relate the structure of echinoderms to essential life How do echinoderms carry out essential functions? ¦ How are echinoderms classified? ¦ How do echinoderms affect other living things? functions. • Describe the characteristics of Echinoderms and Invertebrate Chordates the classes of echinoderms. • Explain how echinoderms fit into the world. 29-2 Invertebrate Chordates • Name and discuss the three distinguishing characteristics of chordates. Nearly everyone who has visited the seashore has seen starfish, sea urchins, sand dollars, or their remains washed up on the beach. These animals are members of the phylum Echinodermata (echino- means spiny; dermis means skin), a phylum that has a long and fascinating history stretching back to the beginning of the Cambrian Period, more than 580 million years ago. • Describe the two subphyla of invertebrate chordates. Journal Activity YOU AND YOUR WORLD The delicate symmetrical appearance of this starfish obscures the fact that starfish are carnivores preying on other forms of sea life. The small tunicate shown in the inset is closely related to vertebrate animals, even though its appearance more closely resembles other simpler animals. Perhaps you have combed a beach for treasures of shells, starfish, or sea-urchin spines, scrambled over grassy dunes, swum in the ocean, or imagined what the seashore is like, In your journal, describe your experiences, whether they are real or imagined. hen most people see a starfish, they immediately think of the ocean—an appropriate reaction, considering that starfish and their relatives live only in the sea. Surprisingly not all of the members of this phylum resemble stars. Some look like graceful long-stemmed flowers; others, like a peculiar cross between a polka-dotted pickle and a stalk of cauliflower. Some are as round and prickly as a pincushion. Others are flat bristly disks with holes and notches around their edges. Still others resemble armored feather dusters, closely related to the vertebrates? You will discover the answers to Figure 29-1 Echinoderm means spiny skin, which as you can see from this sea urchin (bottom) is an appropriate name. The sea cucumber (top) is also an echinoderm. Although its skin is smooth, it shows another characteristic of echinoderms— these questions-'in the pages that follow. five-part symmetry. pentagon-shaped cookies, or the curlicues and flourishes beneath ah old-fashioned signature. What other animals belong to this phylum? How are they all adapted to the ocean world? Why do scientists consider them to be What Is an Echinoderm? As their name indicates, echinoderms (ee-KlGH-nohdermz) are spiny-skinned animals. In addition to having a spiny skin, echinoderms are characterized by five-part radial symmetry, an internal skeleton, a water vascular system, and suction-cuplike structures called tube feet. The internal skeleton, or endoskeleton, is made up of hardened plates of calcium carbonate, which are often bumpy or spiny. Figure 29-2 Starfish, or sea star, species vary greatly. This bat star lives in the ocean off the coast of southern California. Lacking the thin arms of other starfish, this species resembles a pentagon. The water vascular system, which you will learn more about shortly, consists of an internal network of fluid-filled canals connected to external appendages called tube feet. The water vascular system is involved with many essential life functions in echinoderms, including feeding, respiration, internal trans¬ port, elimination of waste products, and movement. Some echinoderms, such as starfish and sand dollars, live in shallow water and are thus familiar to beach-goers. Other echinoderms live only on coral reefs or on the floor of the deep ocean. Although echinoderms possess certain characteristics found in no other animals, living or extinct, they share several important features with members of our own phylum (Chordata). For example, certain stages in the development of echinoderm larvae are remarkably similar to stages seen in some members of the phylum Chordata. In addition, echinoderms have an internal skeleton (as do vertebrates) rather than an ex¬ ternal skeleton (as do other invertebrates). For these reasons, biologists believe that among common invertebrates, echino¬ derms are most closely related to humans. Echinoderm species vary greatly in appearance. Starfish exhibit a fragile beauty and perfection in shape that stirs wonder in most observers. Some sea cucumber species fasci¬ nate because their ugliness has a certain repulsive appeal. Regardless of appearance, however, echinoderms have adapta¬ tions that make them successful survivors in the world of the sea. As you read this section, keep in mind that echinoderms are survivors of history. Their success is confirmed by the fact that some echinoderms alive today look much like their an¬ cient ancestors who lived in the seas millions and millions of years ago. Form and Function in Echinoderms Adult echinoderms have a body plan with five parts organ¬ ized symmetrically around a center. As a result of this body plan, adult echinoderms typically have neither an anterior nor a posterior end and no brain. However, most echinoderms are two-sided. The side where the mouth is located is called the oral surface, and the opposite side is called the aboral surface. All echinoderms have a unique system of internal tubes called a water vascular system. The water vascular system opens to the outside through a sievelike structure called the madreporite (ma-druh-POR-ight). In starfish, the madreporite connects to a tube called the ring canal that forms a circle around the animal's digestive system. From the ring canal, five radial canals extend into each body segment. Attached to each radial canal are hundreds of movable tube feet. The entire water vascular system operates like a series of living hydraulic pumps that can propel water in or out of the tube feet. When water is pushed into a tube foot, the tube foot expands. When water is pulled out, the cup on the end of the tube foot shrinks, Upper part of stomach creating a partial vacuum that holds onto whatever the foot is touching. In this way, the tube feet act like living suction cups. A single tube foot alone cannot accomplish much, but hundreds acting together create enormous force. All echino¬ derms "walk" with their tube feet, and some use their tube feet for feeding. FEEDING Echinoderms have several methods of feeding. Carnivores, such as many species of starfish, use their tube feet to pry open the shells of bivalve mollusks such as clams and scallops. Once the bivalve's shell is opened, the starfish flips its stomach out of its mouth, pours out enzymes, and digests its prey in the prey's own shell. When the starfish has finished dining, it moves its stomach back into its mouth, leaving be¬ hind an empty shell as the only evidence of its deed. Starfish also eat snails, corals, and even other echinoderms. Herbi¬ vores, such as sea urchins, scrape algae from rocks by using their five-part jaw. Filter feeders, such as sea lilies, basket stars, and some brittle stars, use tube feet on flexible arms to capture plankton that float by on ocean currents. Detritus feeders, such as sea cucumbers, move much like a bulldozer across the ocean floor, taking in a mixture of sand and detritus. Then, like an earthworm, they digest the organic material and pass the sand grains out in their feces. Lower part of stomach Figure 29-3 The pressure exerted by the water vascular system of the starfish (left) moves the animal along the ocean bottom. The digestive system of a starfish (right) breaks down food, which is then transported throughout the animal's body in the digestive glands and in the fluid within the body cavity. RESPIRATION Echinoderms, like other animals, need to exchange carbon dioxide for oxygen. In most species the thinwalled tissue of the tube feet forms the main respiratory sur¬ face. In some species small outgrowths called skin gills also function in gas exchange. INTERNAL TRANSPORT The functions of transporting oxygen, food, and wastes—which are performed by the circula¬ tory system in many animals—are shared by different systems 639 spiny defenses of echinoderms. For example, basket stars, feather stars, and spiny sea urchins are very slow moving. Clever fishes (and you will meet some clever fishes in Chapter 31) have learned to turn these animals over and attack them through their unprotected underside. For this reason, many echinoderms hide under rocks and in crevices by day, coming out to feed at night, when most predators are asleep. Figure 29-4 Tube feel, located on the underside of a starfish's arms, are used to perform many life functions (left). Starfish use their tube feet to open clams (right). Once the starfish has opened the clam shell, it flips its stomach out of its mouth and begins to digest the clam right in the shell. No wonder starfish are not welcome in clam beds! in echinoderms. Because respiration (gas exchange) and the removal of metabolic wastes occur through skin gills and tube feet located all over the body, a system to deliver oxygen and carry away carbon dioxide and other wastes is not essential. The distribution of nutrients is performed primarily by the di¬ gestive glands and the fluid within the body cavity. EXCRETION In almost all echinoderms, solid wastes are released through the anus in the form of feces. (The exceptions are brittle stars, which lack an anus and thus release undi¬ gested materials through the mouth.) Echinoderms, like many other marine invertebrates, excrete nitrogen-containing cellu¬ lar wastes primarily in the form of ammonia. Wastes seem to be excreted in many of the same places around the body in which gas exchange takes place—the tube feet and the skin gills. RESPONSE As you might expect in animals that have no head, echinoderms have primitive nervous systems. Most echinoderms have a nerve ring that surrounds the mouth and radial nerves that connect the ring with the body sections. Scattered sensory cells that are sensitive to chemicals released by potential food are also characteristic of most species. Star¬ fish additionally have up to 200 light-sensitive cells clustered in eyespots at the tip of each arm. Although these structures have lenses, they do little more than tell the animal whether it is light or dark. Some echinoderms also possess statocysts (simple organs for balance that tell an organism whether it is right side up). Although you might think that the tough, spiny skins of echinoderms protect them from predators, spines actually offer protection for only a few species—the crown-of-thorns starfish, for example." Many predators have learned ways around the MOVEMENT Most echinoderms use tube feet and thin layers of muscle fibers attached to the plates of the endoskeleton to move. An echinoderm's mobility is determined in part by the structure of its endoskeleton, In sand dollars and sea ur¬ chins, the plates are fused together to form a rigid box that en¬ closes the animal's internal organs. These animals usually have movable spines attached to their endoskeleton, which they use along with their tube feet to creep from one place to another or to burrow in the sand. In starfish, brittle stars, and feather stars, the skeletal plates move around a series of flexible joints, enabling these echinoderms to use their arms for locomotion. Feather stars can swim for short distances by flapping their arms like wings, but starfish and brittle stars are only able to crawl. In sea cucumbers, the plates are reduced to tiny vestiges inside a soft, muscular body wall. The loss of the plates makes the body of sea cucumbers very flexible. Some species are able to crawl along the ocean floor like large, fat worms by contract¬ ing the muscles of the body wall. Figure 29-5 The basket star spreads its branching arms to filter particles of food from the water. When disturbed, the basket star curls up these arms and exposes the armored surface for protection. REPRODUCTION Most echinoderms are either male or female, although some are hermaphrodites. In starfish, the sperm or eggs are produced in testes or ovaries, respectively, which fill the arms during the reproductive season. The ani¬ mals shed their sperm and eggs into the water. Individual star¬ fish detect gametes of their own species in the water, and they respond to that stimulus by releasing their own gametes. Fertil¬ ization takes place in open water, and larvae swim around for some time as members of the huge community of plankton that swarm in the ocean. Eventually the larvae, which have bilateral symmetry, swim to the ocean bottom, where they mature and metamorphose into adults that have radial symmetry. Many starfish have incredible abilities to repair themselves when damaged. In fact, if a starfish is pulled into pieces, each piece can grow into a new animal as long as it contains a por¬ tion of the central part of the body. This ability of a starfish to regenerate itself has caused a great deal of trouble to people who earn their living fishing for bivalves (two-shelled mollusks). In the past, angry shellfishermen who were aware that starfish ate bivalves would tear the animals into two or three pieces and toss them overboard. Imagine their surprise when they noticed even more starfish in their bivalve beds. Today, shellfishermen know that starfish have the ability to regenerate and that every piece of torn starfish they throw back could de- Figure 29-6 Unlike adults, which mostly crawl along the ocean bottom, echinoderm larvae are free- swimming. These larvae resemble closely the free-swimming larvae of invertebrate chordates. 641 The Echinoderm Classes The almost 6000 species of living echinoderms are found in almost every ocean in the world. However, no echinoderms have ever entered fresh water, and they cannot survive for long on land. Although they share certain characteristics, echinoderm species are remarkably diverse in appearance. The fol¬ lowing descriptions of echinoderm classes will provide a brief introduction to these animals. STARFISH This class contains the common starfish, which are also known as sea stars. Starfish occur in many colors, and you may be surprised to learn that many species have more than five arms. Starfish creep slowly along the ocean bottom. Most are carnivorous, preying upon the bivalves they encounter as they move. Some species of starfish are im¬ portant predators in rocky areas along the coast. BRITTLE STARS These animals live in tropical seas, Figure 29-7 The brittle star gets its name from the fact that it can shed its arms when it is threatened (left). This distracts predators so that the brittle star can escape. In time, it wdl re grow the missing arm. Some starfish, such as the sun star, have more than hue arms (right). especially on coral reefs. They look much like a common star¬ fish, but they have longer, more flexible arms and are thus able to move much more rapidly. In addition to using speed for pro¬ tection, brittle stars protect themselves by shedding one or more of their arms when attacked. The detached parts keep wriggling violently, distracting predators, while the rest of the animal escapes. Brittle stars are filter and detritus feeders that hide by day and wander around in search of food only under the cover of night. SEA URCHINS AND SAND DOLLARS This class includes disk-shaped sand dollars, oval heart urchins, and round sea ur¬ chins. Many of these animals, which are found in marine envi¬ ronments all over the world, are grazers that eat large quantities of algae. Others are detritus feeders. Heart urchins and sand dollars live hidden in burrows that they dig in sand or mud. Most sea urchins wedge themselves in crevices in rock during the day and come out only at night. However, many sea urchins have formidable defenses in the form of long, sharp spines. One type of sea urchin even has small blue poison sacs covering the tips of each spine, ensuring that wounds it inflicts will be painful! SEA CUCUMBERS As their name implies, these echino¬ derms look like warty moving pickles with a mouth at one end and an anus at the other. Most sea cucumbers are detritus feeders. Although these animals are not numerous in shallow water, herds containing hundreds of thousands of them often cover areas of the sea floor at great depths. A few species of sea cucumbers expel sticky substances that attach to a predator. The predator, in all probability an attacking crustacean, is im¬ mobilized as it is glued into a helpless ball. Figure 29-8 The slate urchin (top, right) has thick, strong spines that were once harvested for use as implements for writing on slateboards—thus, its name. Sea urchins have a lanternlike set of bony plates inside their body that power their jaws (inset). The sand dollar (top, left) gets its name from its flattened, coin-shaped appearance. SEA LILIES AND FEATHER STARS These filter feeders, which have 50 or more long, feathery arms, comprise the most ancient class of echinoderms. Although sea lilies and feather stars are not common today, a rich fossil record indicates that 643 they were once widely distributed. Sea lilies are sessile animals that are attached to the ocean bottom by a long, stemlike stalk. Modern sea lilies live at depths of 100 meters or more. Many feather stars live on coral reefs, where they perch on top of rocks at night and use their tube feet to catch floating plankton. How Echinoderms Fit into the World Echinoderms are numerous in most marine habitats. In many areas, starfish are important carnivores that control the populations of other animals. Sometimes their numbers rise or fall suddenly, causing major changes in the numbers of other forms of marine life. For example, several years ago the coraleating crown-of-thorns starfish suddenly appeared in great numbers over wide areas of the Pacific Ocean. Within a short span of time, these starfish caused extensive damage to many coral reefs. The extent of their damage surprised and alarmed marine biologists, many of whom took drastic action to kill the starfish by injecting them with poisonous chemicals. We still do not know what caused this population explosion in the crownof-thorns starfish or what will be its long-term effects on coral reefs. Figure 29-9 Acting much like a living vacuum cleaner, this sea cucumber (top) moves along the ocean bottom swallowing organic material along with sand. Sea lilies (center) and feather stars (bottom) feed by filtering floating organic material from the water. The names reflect the delicate beauty of these animals. In many coastal areas, sea urchins are important because they control the distribution of algae. However, if present in large numbers, they can threaten to literally "eat out of house and home" the other dwellers that share this habitat. In various parts of the world, some echinoderms—for ex¬ ample, sea urchin eggs and sea cucumbers—are considered delicacies by some people. Many more echinoderms, however, are useful as research subjects and as possible sources of medi¬ cine. Several chemicals extracted from starfish and sea cucum¬ bers are currently being studied as potential anti-cancer and anti-viral drugs. Sea urchins have been the subject of pioneer¬ ing studies in embryology. These animals are easy to study be¬ cause they produce large eggs that are fertilized externally and develop in plain sea water. Sea urchin embryos also make ex¬ cellent subjects for testing the effects of drugs on cell division and development. SECTION REVIEW 1. What is an echinoderm? Name five kinds of echinoderms. 2. How do tube feet help echinoderms to carry out their essential life functions? 3. How do starfish move? How do starfish open bivalves? 4. Connection—Ecology Why is tearing a starfish apart and throwing it back into the water not a good way to limit a starjish population? 644 29-2 Invertebrate Chordates Guide For Reading The phylum Chordata. to which fishes, frogs, birds, snakes dogs cows and humans belong, will be the subject of many of the chapters to come. Most of the chordates vertebrates, which means that they have backbones, so they are placed in the subphylum Vertebrata. But there are also some invertebrate chortates. The ¦"-rtebrate chordates are divided into two subphyla-tumcates and lanceleta Because thev show possible links between vertebrates and the rest o the animal kingdom, the invertebrate chordates are of great What are chordates? What are invertebrate chordates? What are the distinguishing characteristics of chordates? Why are invertebrate chordates important to evolutionary biologists? evolutionary interest. What Is a Chordate? Members of the phylum Chordata are chorda^' Chordates are animals that are characterized by a notochord a hollow dorsal nerve cord, and pharyngeal (thro ) slits Some chordates possess these distinguishing characteris¬ es as adults; Others, only as embryos. However, all chorda es display these three characteristics at some stage of their lite. The first chordate characteristic, the notochord, m a lonsh flexible supporting rod that runs through at least part of the body usually along the dorsal surface just beneath the nerve cord' Most chordates have a notochord only during the early part of embryonic life. In most vertebrates, the notochord is -^VtSrirracteristic, the hollow do.al nerve cord runs along the dorsal surface just above the noto¬ chord. Remember that in most invertebrates, nerve cords run along ventral surfaces. In most chordates, the front end of this nerve cord develops into a large brain. Nerves 'his cord at regular intervals along the length of the animal and connect to internal organs, muscles, and sense organs. The third chordate characteristic, pharyngeal slits are paired structures in the pharyngeal (fuh-RmH-jee-uhO o throat, region of the body, (Remember that pharynx anothe word for throat.) In aquatic chordates such as lancelets and fishes the pharyngeal slits are gill slits that connect the pharvngeal cavUy ^th the outside. The location of gills is very im¬ portant Many invertebrates have gills of some sort in variou places but only chordates have pharyngeal gills. In terrestna chordates that use lungs for respiration, pharyngeal slits are present for only a brief lime during the development of he embrvo These slits soon close up as the embryo develops In chordates such as humans, pouches form in the pharyngeal reion but never open up to form slits, ^r this reason some sci¬ entists regard pharyngeal pouches, not slits, as the chordate characteristic. TUNICATES Tunicates are small marine chordates that eat plankton they filter from the water. They get their name Figure 29-10 Although it seems like a simple animal, the tunicate is a chordate. It is, therefore, a relatwe of ours—although a very distant one. from a special body covering called the tunic. Only the tad¬ pole-shaped larvae of tunicates have a notochord and a dorsal nerve chord. When most tunicate larvae mature, they undergo metamorphosis and become sessile adults that grow into colo- aTltsirf h0 3 ^ SUrfaCe- B0th 'arval tunicates and adults filter feed and breathe at the same time through a pha¬ ryngeal basket pierced by gill slits. LANCELETS The small fishlike creatures called lancelets ive in the sandy bottom of shallow tropical oceans. Unlike tun¬ icates, adult lancelets have a definite head. They have a mouth nair.Tf^n1".-? a, g Pharyn§eaI region with up to a hundred pairs of gill slits. Lancelets feed by passing water through their pharynx, where food particles are caught in a sticky mucus. is mucus is swallowed into a digestive tract that starts at one nd of the pharynx and continues straight through the animal to the anus, near the tail. ^aVe 3 simP,e' P"mitive heart that pumps blood Figure 29-11 Sea squirts are tunicates. /Ls' adults, these organisms are sessile, living firmly attached to one place. However, the larvae of these animals, like the larvae of echinoderms, are free-swimming. The Secret Life of Salps once mysterious open-water tunicates known Once scuba-diving scientists became suffi¬ ciently experienced (and sufficiently brave) to hop off their boats in the middle of the ocean, however, our knowledge of salps increased dramatically. It became clear that salps are everywhere. Giant herds of salps drift just be¬ neath the surface. Certain species form huge snakelike colonies that stretch for many Sometimes a remarkably simple change in the techniques biologists use to study the world causes us to alter our ideas about the way the living world works. For example, the invention of the microscope opened up the world of "unseen life." Recently, new methods have contributed to our understanding of the as salps. meters. lanrf»i t Ve*seis In a closed circulatory system. Additionally, ancelets show evidence of segmentation in the arrangement of n nerves and muscles. A lancelet's muscles are organized to V-shaped units that are paired on either side of the body Each muscle unit receives a branch from the main nerve cord A similar segmented nerve and muscle organization is found in all living vertebrates. Unlike most vertebrates, lancelets have no jaw. Their mouth is composed entirely of soft tissues. LanceJets also lack appendages and can move only by bending their bodies back and forth. 8 Salps are free-swimming animals that live in the open sea. Biologists have known about their existence for many years, but they knew little about their importance. This was due to the fact that research vessels had no way of collecting and identifying salps. These beauti¬ ful animals are so fragile that they literally fall to pieces if they are handled roughly. And that was exactly what happened in the collecting nets marine biologists used to gather plankton. Any salps that entered the net were squeezed How Invertebrate Chordates Fit into a clear, featureless mush. By collecting salps carefully, researchers have learned how they live. In many places, salps form important links in the ecology of the open sea. Salps eat certain plankton and are themselves food for other plankton, sea turtles, and certain fishes. This new knowledge has come to light because of a simple change in research techniques. Although these vital creatures have been nearly ignored for dec¬ ades, marine biologists can now study them closely and discover how they fit into the web of life. into the World Figure 29-12 Lancelets are small fish/ike creatures that often live with their body half buried in sand. They filter food particles from the water. In some ways, studying invertebrate chordates is like using a time machine to study the ancestors of our own subphylum. It is important to remember that living vertebrates did not evolve from hying lancelets or tunicates. Both these subphyla have evolved oyer time. However, similarities in structure and embryolog'cal development indicate that vertebrates and inverteb ate chordates evolved from common ancestors many millions of years ago. 1. What characteristics are found in a chordate? 2. What characteristics of tunicates and lancelets make them seem like close relatives of vertebrates? 3. Critical Thinking—Making Comparisons Which characteristics of tunicates and lancelets are unlike vertebrate cbaracteristics? Salps are free-swimming invertebrate chordates found in the open ocean. 647 r u d E imj S 1r ii ii ¥ 6 I %& •v 1 G ECHINODERMS PROBLEM SUMMARIZING THE CONCEPTS How can echinoderms be identified? Specimen Identity of Specimen Identification (from Identification Key) MATERIALS (per group) Number 1 assorted echinoderms (pictures or preserved specimens) 29-1 Echinoderms 2 • Echinoderms are spiny-skinned animals with five-part radial symmetry, an internal skele¬ 3 4 PROCEDURE L^- 1. On a separate piece of paper, draw a data table similar to the one shown here. 2. Your teacher will provide either pictures or preserved echinoderm specimens. Each speci¬ men will be numbered. 3. Use the key to identify each numbered speci¬ men. Start at step 1 and read descriptions A and B. Only one of the descriptions correctly applies to the specimen you are examining. At the end of a description is the identity of the specimen or directions to proceed to another step. Continue to follow the directions step by step until you identify the specimen. 4. After you identify the specimen, write its name next to its identification number in the data table. Then proceed to the next numbered derms are important predators in many environments. ton, a water vascular system, and suction- —- OBSERVATIONS 1. What feature did all of the echinoderms you examined have in common? 2. How did the echinoderms you examined differ? 3. Did any echinoderms with visible differences have the same identity? ANALYSIS AND CONCLUSIONS 1. How is the use of an identification key similar to the process of classification? 2. Why is it possible for two organisms that look different to have the same identity based on specimen. The key concepts in each section of this chapter are listed below to help you review the chapter content. Make sure you understand each concept and its relationship to other concepts and to the theme of this chapter. the key used in this investigation? 29-2 Invertebrate Chordates cuplike structures called tube feet. • Echinoderms are marine animals; no echino¬ derms live in fresh water or on land. Certain stages in the development of echinoderm larvae are similar to stages seen in members of the phylum Chordata. • All echinoderms have a water vascular sys¬ tem that opens to the outside through a sievelike structure called the madreporite. • In a starfish, the madreporite connects to a tube that leads to the ring canal, a part of the water vascular system, which forms a circle around the starfish's digestive system. Nu¬ trients are moved around the animal in the digestive glands and the body cavity. • Starfish reproduce externally by pouring eggs and sperm into the ocean water. The larvae that result from a fertilized egg float as part of the plankton. • In spite of their fragile appearance, echino¬ • Most chordates are vertebrates, which means they have backbones. However, a few chordate species are invertebrates. There are two subphyla of invertebrate, chordates —tunicates and lancelets. • At some stage of their life, all chordates pos¬ sess these distinguishing characteristics: a notochord, a hollow dorsal nerve cord, and pharyngeal (throat) slits. • Tunicates are small chordates that live in the ocean. Tunicate larvae resemble tadpoles and can move around in the water. • Lancelets are small fishlike creatures that live in sandy ocean bottoms. Adult lancelets have a definite head. 9 Invertebrate chordates are important be¬ cause they indicate that vertebrate and in¬ vertebrate chordates evolved from common ancestors many millions of years ago. Identification Key 1 A. Has obvious radial symmetry B. Appears to have bilateral symmetry Go to 2 A. Has arms or branches Cucumber B. Spherical, oval, or disk shaped Co to 3 3 A. Arms in multiples of five Go to 5 B. Arms are branched and feathery Go to 4 4 A. Arms are long, slender, and flexible Go to 7 B, Arms are thick and less flexible Star o A. Spherical; covered with spines Starfish B. Not spherical Sea Urchin 6 AOval Go to 6 B. Flattened disk Urchin 7 A. Has a long stalk !. Sand Dollar B. Stalk short or absent Sea Lily ' 648 ' ""' Feather Star REVIEWING KEY TERMS Vocabulary terms are important to your understanding of biology. The key terms listed below are those you should be especially familiar with. Review these terms and their meanings. Then use each term in a complete sentence. If you are not sure of a term's meaning, return to the appropriate section and review its definition. 29-1 Echinoderms echinoderm water vascular system tube feet 29-2 Invertebrate hollow dorsal Chordates nerve cord chordate notochord pharyngeal slit 649 CONTENT REVIEW B. In each of the following sets of terms, three of the terms are related. One term does not belong. Determine the characteristic common to three of the terms and then identify the term that does not belong. Multiple Choice Choose the letter of the answer that best completes each statement. 1. A kind of echinoderm that is eaten by some 5. Digested nutrients are moved around the people is a body of a starfish in its a. sea urchin. c. starfish. a. skin gills. c. bony plates. b. digestive glands, d. water vascular b. sea lily. (j lancelet. 2. To open a clam, a starfish uses its system. a. tube feet. c. madreporite. b. brain. d stomach. 6. Tunicates and lancelets are examples of a. vertebrates. c. echinoderms. 3. Echinoderms have ^ ^sh- d. chordates. a. a backbone. b. a long history on Earth. c. lungs. 7. The side of an echinoderm where the mouth is located is called the a. aboral surface. c. oral surface. d. smooth skin. 4. Echinoderms show a. bilateral symmetry. b. top and bottom symmetry. b. tunicate. d. vascular surface. 8. Invertebrate chordates lack a c. radial symmetry. d. no symmetry. a. larva. c. nerve cord. b. notochord. d. backbone. True or False 5. 6. 7. 8. starfish, sea lily, lancelet, sea urchin ring canal, radial canal, tube feet, skin notochord, hollow dorsal nerve cord, pharyngeal slits, vertebrae tube feet, brain, water vascular system, madreporite CONCEPT MASTERY Use your understanding of the concepts developed in the chapter to answer each of the following in a brief paragraph. 5. How do starfish reproduce? 1. What is radial symmetry? Name an animal 6. How does a sea cucumber feed? that shows this kind of symmetry. 7. What characteristics does a lancelet share 2. Briefly explain how a starfish eats a clam. with vertebrate chordates? 3. How does the water vascular system of a 8. Why is it not a good idea to break up a starfish help this animal to move? starfish and throw the pieces back into the 4. What structures on a starfish tell this water, especially if you fish for oysters? animal about its environment? CRITICAL AND CREATIVE THINKING Determine whether each statement is true or false If it is true, write "true." If it is false, change the underlined word or words to make Discuss each of the following in a brief paragraph. 1. All echinoderms have bilateral symmetrv. fi 2. In echinoderms. tube feet and skin gills used in respiration and excretion. 7 3. Lancelets have a primitive heart. 4. Echinoderms have nerves attached to 8 plates in their endoskeleton. 1. Making predictions Suppose that you are living alone on a small tropical island in the Pacific Ocean. This island is protected by a coral reef that surrounds it. One day while you are skin diving, you notice several crown-of-thorns starfish eating some of the coral animals that are part of your the statement true. 5. A sea cucumber is a herbivore. Tube feet are able to create suction when air is pumped out of them. Some echinoderms have madreporites that tell them whether they are right side up. If a piece of a starfish contains a portion of the central part of the body, the piece is able to regenerate. Word Relationships A. An analogy is a relationship between two pairs of words or phrases senera/lv wrmen ,n the fo lowing manner: abed. The symbol: is read Cto'andthe anTa'l aj^ls toplan,^^ ^ * - reef. Predict what might happen if the crown-of-thorns starfish increase in number. 2. Making comparisons Compare the form and function of a starfish and a sea cucumber. Describe the animals' adaptations for movement and feeding. 3. Applying concepts Explain why many 1. starfish:echinoderm::tunicate: 2. sea cucumberrdetritus feeder::feather smr ~ 3. eyespots:light::statocysts: 4. madreporite.aboral surface::mouth:__ fertilized starfish eggs never develop into adult starfish. 4. Designing an experiment Your friend tells you that starfish can regenerate themselves from even a small portion of an arm. You challenge this assumption. Design an experiment to prove who is correct. 5. Using the writing process Suppose that humans had the ability to regenerate themselves. For example, an arm might be able to grow a whole new body. Write a science fiction story that describes how this process might work for a person who was severely injured in an automobile accident.