11 echinoderms - washingtonville central school · pdf fileidentify the important...

When you have completed this chapter, you should be able to:

IDENTIFY the important characteristics of all echinoderms.

DISTINGUISH among the five main groups of echinoderms.

DISCUSS some important life functions of the echinoderms.

While slowly moving across the surface of a coral reef, the crown-of-thorns sea star (Acanthaster planci) devours the coral animals in itspath. A voracious predator, the crown-of-thorns is responsible for thedestruction of coral reefs around Hawaii and other tropical islands inthe South Pacific.

Sea stars, or starfish, are invertebrates that have a spiny skin cover-ing, among other unique features. Such spiny-skinned animals areclassified in the phylum Echinodermata (meaning “spiny skinned”).This group also includes such animals as the sea urchin, brittle star,and sea cucumber. In this chapter, you will learn how these exclusivelymarine animals are adapted to the ocean environment.

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11.1Stars in the Sea

11.2Adaptations in theSea Star

11.3Sea Urchins andSand Dollars

11.4EccentricEchinoderms

Echinoderms

MARINE INVERTEBRATES

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11.1 STARS IN THE SEA

Stroll along a beach and you might see a “starfish” clinging to rocksat the water’s edge. These bottom-dwelling invertebrates are not fishat all; they have neither scales nor a backbone. In fact, starfish, orsea stars, as they are now more appropriately called, are types ofechinoderms—spiny-skinned animals that lack body segmentationbut have radial symmetry (usually five-part) and an internal skele-ton. In radial symmetry, all similar body parts are regularly arrangedaround the central point of an animal’s body.

There are more than 5000 species of echinoderms, which areplaced in five main classes: sea stars; sea urchins and sand dollars;brittle stars; sea lilies and feather stars; and sea cucumbers. This firstsection describes the familiar sea stars, members of the class Aster-oidea, as representative of this phylum.

Types of Sea Stars

Sea stars are found from the subtidal zone to the deepest parts ofthe ocean. These echinoderms usually have five (or multiples of five)appendages, or arms, radiating out from a central body—hence the“star” in their name. However, there is great variety among the seastars.

The common Atlantic sea star (Asterias), which looks typical, isfound in mussel and clam beds along the East Coast. (See Figure11-1.) Likewise, the West Coast sea star (Pisaster) is found in beds ofCalifornia mussels. The seafood industry regards sea stars as pests,because they can eat large numbers of commercially importantbivalves. The bat star (Patiria), whose five arms are connected in aweblike structure like the wings of a bat, is commonly found inkelp beds along the West Coast, from Alaska to California. Anotherechinoderm from the Pacific, the sun star (Solaster), has 10 to 15arms. The sun star lives on a variety of ocean bottoms, from lowtide to depths of more than 400 meters. Sun stars are atypical inthat they prey on other sea stars and even eat members of theirown species. (See Figure 11-2.)

260 Marine Invertebrates

Figure 11-1 The commonAtlantic sea star Asterias.

11.1 SECTION REVIEW

1. Why is it more accurate to say “sea star” than “starfish”?

2. List some important characteristics of the sea stars.

3. Why do some people consider sea stars to be pests?

11.2 ADAPTATIONS IN THE SEA STAR

Sea stars often lose an appendage in struggles with other marine ani-mals. When a sea star loses an arm, it can grow another one back, orregenerate it, as evidenced by the fact that one arm will be notice-ably shorter than the others.

The spines that give sea stars their characteristic rough skin arecomposed of calcium carbonate (CaCO3). The spines are connectedto an internal skeleton, or endoskeleton, within the skin, also com-posed of CaCO3. The spiny covering helps support and protect theechinoderm.

Sea stars breathe through their skin and through their tube feet.On the dorsal surface of the skin are small, ciliated fingerlike pro-jections called skin gills. Oxygen from the water diffuses throughthe thin membrane of the tube feet and skin gills into a fluid-filledspace under the skin called a coelom. The coelom is lined with cili-ated cells that beat back and forth to circulate oxygenated fluid

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Sun star (Solaster)Bat star (Patiria)

Figure 11-2 Two Pacificsea stars—the bat starPatiria, which has a web-like structure, and the sunstar Solaster, which has upto 15 arms.

around the body. Cell wastes and carbon dioxide diffuse from thecoelom through the skin gills and tube feet to the outside. In effect,the sea star has an open circulatory system.

Feeding and Locomotion in the Sea Star

Sea stars use their arms for locomotion and for food-getting. Theunderside, or ventral surface, of each arm contains numerous littletube feet located in a groove. At the end of each tube foot is a suc-tion disk. When the suction disk comes into contact with a hardsurface, it clings to that surface. Muscles in the tube feet control theclinging and pulling actions that enable the sea star to move. This“walking” motion helps the sea star find its food. In addition, as dis-cussed above, for most echinoderms the thin walls of the tube feetserve as an important respiratory surface for the exchange of gases.(See Figure 11-3.)

Bivalve mollusks are a favorite food of the sea star. How does asea star open up a clam? The sea star uses its hundreds of tube feetto grasp the clam and cling onto each of its shells. The tube feetexert a force that pulls the two shells in opposite directions. Whenthat force is applied for several hours, the adductor muscles insidethe clam become tired, and the clam opens.


Grooves

Arms

TubefeetMouth

Ventral surfaceFigure 11-3 Externalanatomy of a sea star(ventral view).

How does the sea star consume the clam? Since clams are usu-ally too big to fit through a sea star’s mouth (located in the center ofits underside), the sea star pushes its thin, membranous stomachout through its mouth to engulf the food. (In some cases, the seastar’s stomach can be pushed into a shell that is not tightly shut,without the tube feet first prying the shell open.) Digestive enzymessecreted by the sea star’s stomach digest the food externally. The seastar then pulls back its stomach, which contains the digested foodparticles. Nutrients are absorbed and transported to its body cells inthe fluid-filled coelom. Wastes are eliminated through the anus.(Undigested wastes, such as shell fragments, are eliminated throughthe mouth.)

Locomotion is necessary for food-getting by sea stars. How ismovement accomplished? A network of water-filled canals andtubes, called the water vascular system, enables movement in seastars. Tracing the pathway of water through this system will helpyou to understand how it works. (See Figure 11-4.) Water enters thesea star (when there is a loss of internal liquid) through a small filtercalled the sieve plate, also called the madreporite. The sieve plate isfound on the topside, or dorsal surface, of the sea star near its cen-

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Dorsal surface

Radialcanal

Digestivegland

Upper partof stomach

Tubefeet

Spines

Stonecanal

Sieveplate

Eyespot

Arm

Centraldisk

Ringcanal

Anus

Groove

GonadMouth

Coelom

Ampullae

Figure 11-4 External andinternal (cut-away)anatomy of a sea star(dorsal view).

ter, an area referred to as the central disk. After entering, the waterpasses down through a short stone canal, then into a circular ringcanal within the central disk. From the ring canal, the water flowsthrough the radial canals. There is one radial canal in each arm.Many tube feet are connected to each of the radial canals.

Movement occurs when water enters the tube feet. At the topof each tube foot is an ampulla, a structure that resembles the rub-ber bulb on a medicine dropper. After the ampulla fills with waterfrom the radial canal, it contracts. This contraction of the ampul-lae (by ampullar muscles) forces water into the tube feet, causingthem to extend. Then, when the tube feet make contact with a sub-strate, circular and longitudinal muscle fibers within them contract,forcing water back into the ampullae. This exit of water from thetube feet creates the suction that holds the sea star to a substrate orclamshell. The sea star uses this suction force to push and pull itselfalong or to open a bivalve shell.

Sea Star Response, Reproduction,and Regeneration

Sea stars are sluggish creatures and slow to respond to stimulibecause they have a simple nervous system. However, they canrespond to stimuli such as changes in the amount of light. Tinylight receptors, called eyespots, are located at the end of each arm.The eyespots convert light into electrical impulses, which are car-ried by nerves to a central nerve ring that encircles the mouth. Thenerve ring coordinates the movements of the arms by sending mes-sages to and from radial nerves located in the arms.

Sea stars have separate sexes, but the sexes look identical so youcannot know the sex by looking at them. You have to examine thesea star internally. Look at the cross section of part of a sea star’sarm. (Refer to Figure 11-4). Gonads are located inside each arm, nearthe central disk. Ovaries and testes shed the eggs and sperm, respec-tively, into the water through openings found between theappendages. Both fertilization and development occur externally.

Sea stars can also increase their numbers through regeneration. Ifan arm is torn off during a struggle (for example, with a predator), anew arm can be regenerated; and a whole new sea star can grow fromthe severed appendage, provided part of the central disk is present.


The lab investigation at the end of this chapter will give you abetter understanding of the sea star’s external anatomy.

11.2 SECTION REVIEW

1. How does a sea star open a bivalve such as a clam?

2. Explain how a sea star uses its tube feet to move.

3. Describe ingestion and digestion in a sea star.

11.3 SEA URCHINS AND SAND DOLLARS

The echinoderm with the most impressive spines is definitely thesea urchin, a member of the class Echinoidea. The sea urchin’smovable spines are attached to its internal skeleton, which isformed by bony plates that are fused. (As in the sea star, both thespines and endoskeleton are made of CaCO3.) This endoskeleton,which remains when a sea urchin dies, is sometimes found washedup on a beach. It has an attractive pattern of raised bumps, evidenceof the former attachment points for the spines.

The animals in this class, which also includes sand dollars andsea biscuits, are characterized by oval or round bodies that lack arms.They are the only echinoderms that use both their spines and tubefeet to move. Sea urchins inhabit the intertidal and subtidal zonesalong rocky coasts. They move very slowly along the rock surfaces,scraping off algae with their unique five-toothed mouth structure,called an Aristotle’s lantern (because of its resemblance to an ancientGreek lantern). Along the rocky coasts of Maine, California, thePacific Northwest, and elsewhere in the world, sea urchins do such agood job of grazing that they often scrape the rocks bare of seaweeds.

Predation and Protection Among Sea Urchins

In shallow tropical waters, be careful where you walk—you couldstep on the long-spined sea urchin (Diadema). The sharp spines caninflict a very painful puncture wound. In some species, the spinesmay be hollow and contain toxins as well. Other species of seaurchin, such as the purple sea urchin (Arbacia) and the green sea

Echinoderms 265

urchin (Strongylocentrotus), which graze on seaweeds along thePacific Coast, have shorter, thicker spines. For protection frompredators and strong wave action, sea urchins often use their spinesto wedge themselves in the spaces between rocks. (See Figure 11-5.)The rock-boring urchin (Echinometra) that inhabits the Caribbeantakes this a step further—it uses its teeth to bore into the rock, form-ing a cup to hide in.

The spines of the sea urchin are a natural protection againstmost predators, except the California sea otter. The sea otter (seeChapter 14) is a marine mammal that dives to the ocean floor tohunt for sea urchins. After picking up a sea urchin, the sea otterswims to the surface, rolls over on its back, then places the seaurchin on its chest. Using a rock that it also picks up from theseafloor, the sea otter cracks open the sea urchin and eats the con-tents. Humans also eat sea urchins. In many countries, sea urchinsare considered a delicacy because of the eggs they contain.

Life Cycle of the Sea Urchin

There are male and female sea urchins but, as with the sea star, youcannot tell the animal’s sex just by looking at it. During the breed-ing season, the female sea urchin releases a great number of largeeggs into the water. Sperm released from the male sea urchin fertil-izes the eggs externally.

The processes of fertilization and development in the sea urchincan be easily observed under the microscope. For this reason, biolo-gists use the sea urchin in embryological studies. A useful feature oftheir development is that up to the blastula stage, all the cells of theembryo are identical—if separated from the embryo, each cell can


Hatpin sea urchinGreen sea urchin Long-spinedsea urchin

Figure 11-5 Three repre-sentative sea urchins; theseechinoderms use boththeir tube feet and spinesfor locomotion.

develop into a separate, identical animal. Much of what we knowtoday about embryology has come from studies done on the seaurchin. Like those of the other echinoderms, embryos of the seaurchin go through a free-swimming larval phase. The larvae, whichare bilaterally symmetrical, live as part of the plankton communityuntil they settle on the seafloor and develop into adult sea urchins.(See Figure 11-6.)

Sand Dollars and Sea Biscuits

The sand dollar (Echinarachnius) looks like a large coin (hence itsname), and has short spines covering its skin. Sand dollars use theirspines to burrow in the sand, where they feed by catching plank-ton and organic debris in sticky strings beneath their spines. Thefood is then pushed toward the mouth. Members of this class havea well-developed intestine and anus, through which the food isdigested and eliminated, respectively. When a sand dollar dies andits soft parts decay, the flat internal skeleton of calcium carbonateremains. People often collect these attractive “shells,” which have adistinctive star-shaped pattern on them. (See Figure 11-7.)

Closely related to the sand dollar is the sea biscuit (Plagiobris-sus). However, this echinoderm is more rounded (like a biscuit), haslonger spines, and inhabits the sandy seafloor around coral reefs.Sea biscuits feed on organic debris and algae.

11.3 SECTION REVIEW

1. Compare food-getting in sea stars and sea urchins.

2. By what method do sand dollars feed? What do they eat?

3. Why is the sea urchin considered a good organism for embry-ological studies?

Echinoderms 267

Blastula Gastrula Larva(early)

Larva(late)

Adultsea urchin

Sand dollar

Figure 11-6 Develop-ment of the sea urchin,from zygote to adultstage.

Figure 11-7 The sand dol-lar uses its short spines forburrowing in the sand; its“shell,” or internal skele-ton, has a unique pattern.

11.4 ECCENTRIC ECHINODERMS

The sea urchin and the sea star are probably the most commonlyencountered echinoderms. Species of echinoderms that may be lessfamiliar to you are described below.

More “Stars” in the Sea

One of the most curious of the echinoderms is the brittle star, whichis placed in its own class, Ophiuroidea. Although they are actuallythe most abundant of the echinoderms (in terms of both numbersof species and individuals), brittle stars (such as Ophiopholis, Ophio-coma, and Ophioderma) are not very obvious because they arenocturnal, bottom-dwelling animals that hide under rocks during

the day. Brittle stars live in theintertidal zone, from the arctic tothe tropics. A subgroup of brittlestars, called basket stars (Gorgono-cephalus), have coiled, branchingarms and live on the deep oceanfloor, thousands of meters belowthe surface.

Unlike the sea stars, brittlestars have a distinct, flattened cen-tral disk; and they do not use theirtube feet for movement. Rather,they have muscles in their long,narrow flexible arms that enablethem to scurry rapidly about onthe seafloor, looking for morsels offood. (See Figure 11-8.) The brittlestar is so named because of its del-icate appearance and its ability to

detach its arms when attacked, thus evading predators. Like the seastars, brittle stars can regenerate their missing arms.

Brittle stars have more than one feeding method. They can usetheir arms to gather organic debris from the seafloor, to capture liveinvertebrates, to filter-feed by trapping bits of food in sticky strands,


Central disk

Brittle star

Flexible arms

Figure 11-8 The brittlestar uses its long flexi-ble arms to move andto catch food.

CONSERVATIONIn a “Pickle” over the Sea Cucumber

1. Why are some people concerned about the harvest of Galápagos sea cucumbers?

2. What groups of people are involved in this controversy? Defend the position of one group.

3. Describe a possible compromise (solution) that might satisfy all the parties involved.

4. How is sustainability of the harvest related to survival of the sea cucumber?

QUESTIONS

Echinoderms 269

It doesn’t look very appetizing, this spiny-skinned, oblong-shaped animal. Yet in South-east Asia, a single cooked and dried seacucumber is considered a delicacy and sells for$80. With interest in, and profits from, the seacucumber so high, the demand for these echin-oderms has far outstripped their numbers inlocal South East Asian waters. So, the seacucumber fishing federation turned to the Galá-pagos Islands, located over 900 km off the coastof Ecuador, as a potential source of this item.Although much of the area has been declared anational park by Ecuador, the islands are hometo 15,000 people, most of whom make their liv-ing from the sea.

By 1992, about 30 million sea cucumbershad been collected from the waters around theGalápagos Islands. Scientists were concernedthat the echinoderm was in danger of beingover-harvested. So, the government of Ecuadorimposed a one-year ban on the harvest, fol-lowed by a partial ban. Then, in the mid-1990s,Ecuador established a fishing season and quotasto reduce over-harvesting. Unfortunately, theseconservation measures were not successful. Bythe late 1990s, more than 6 million sea cucum-bers were being harvested each year. In 1999, acomplete ban on commercial fishing of seacucumbers was enacted. This led to strikes and

protests by the local fishermen, and to anincrease in the illegal harvest of sea cucumbers.

The ban was lifted again in 2002, based on the outcome of a scientific study of the seacucumber population and on a meeting thatincluded local fishermen, government officials,and the scientific community. Stricter guidelinesand new quotas for the harvest were estab-lished. Now, all fishermen will be licensed; theharvest will be permitted in designated areasonly; and monitors will be hired to check forcompliance.

Hopefully, a compromise has been reachedthat will allow the development of a sustainableharvest of Galápagos sea cucumbers (one thatdoes not threaten their survival). Then, all par-ties concerned will no longer be in a “pickle”over these unlikely objects of desire.

or to capture suspended food bits with their tube feet—all of whichis brought into their jawed mouth.

“Lilies” and “Feathers” in the Sea

The sea lilies and feather stars—members of the class Crinoidea—look much more like flowers than like animals. Known as crinoids,they are the most ancient group of echinoderms, having originatedhundreds of millions of years ago. The body of a crinoid is com-posed of dozens of feathery arms, usually perched atop a jointedstalk. Crinoids generally have just a limited ability to move. The sealilies are sessile; they live attached by a stalk to the ocean bottom.(See Figure 11-9.) The feather stars mostly crawl along coral reefs,but some swim by flapping their arms. Using a type of feeding sim-ilar to that of the brittle stars, crinoids filter feed by waving theirarms, thereby capturing bits of zooplankton in their tube feet(which then pass the food to the mouth). Like the brittle stars,crinoids do not use their tube feet for locomotion.

“Cucumbers” on the Seafloor

At first glance, members of this last group of echinoderms do notlook much like echinoderms; in fact, they do not even look like ani-mals! However, on closer examination you can see that the seacucumber—whose soft, oblong body lacks arms—has tube feet thatare arranged in five rows, similar to the five-part radial pattern seenin the sea star. The sea cucumbers, which are placed in the classHolothuroidea, have lost the endoskeleton and spines typical oftheir phylum, retaining only small bony pieces in the skin. Theylive on sandy and rocky seafloors in intertidal and subtidal zonesand are most abundant at great depths. (See Figure 11-10.)

Sea cucumbers such as Holothuria use their sticky, branching ten-tacles—which are actually enlarged tube feet—to trap microscopicorganisms. The tentacles, which are located around the mouth, areextended during feeding and retracted when the animal is dis-turbed. Members of the genus Cucumaria that live on the East andWest coasts have five rows of tube feet along their bodies, which areused for slowly moving along the substrate and for trapping food


Sea lily

Sea cucumber

Figure 11-9 The sea lily is a sessile crinoid withfeathery arms, used forfilter feeding.

Figure 11-10 The seacucumber has five rows oftube feet, used for feedingand movement.

particles in the sand. Sea cucumbers have a one-way digestive tract;wastes are excreted through the anus. Whereas most echinodermsexchange gases through their tube feet and skin gills, sea cucum-bers take in and release water through their anus. Gas exchangethen occurs inside the coelom across the membranes of a structurecalled the “respiratory tree.” Another unusual feature of the seacucumber is that it can release its digestive organs when disturbedby a predator, thus leaving a meal for the predator while it escapes.It later regenerates the lost organs.

11.4 SECTION REVIEW

1. Describe some feeding methods of the brittle stars.

2. What is the basic structure of a crinoid? How does it feed?

3. What features of the sea cucumber show it is an echinoderm?

Echinoderms 271

Laboratory Investigation 11


PROBLEM: How is the sea star adapted for carrying out its life functions?

SKILL: Identifying relationships between body structures and life functions.

MATERIALS: Living sea star, pan of seawater, hand lens, fresh clam or mussel.

PROCEDURE

1. Put a sea star, dorsal side up, in a shallow pan and cover it with seawater.Use the sea star diagrams in Figures 11-3 and 11-4 as a guide. How manyarms or appendages does the sea star have? Make a sketch of your sea star.Label one of the arms in your drawing.

2. Feel the skin of the sea star. Then examine the skin with a hand lens. Noticethe short spines, which you were able to feel. The spines are connected to anendoskeleton, which is composed of calcium carbonate (like the shells ofmollusks). Label the spines in your drawing.

3. How does the sea star breathe? Examine the skin with your hand lens. Lookfor tiny fingerlike projections, called skin gills. Oxygen diffuses from the waterthrough the thin membrane of the skin gills and into the coelom.

4. Locate the sieve plate, or madreporite, which is a white or orange spot onthe dorsal surface. Water enters through the sieve plate, then passes througha network of canals that ends in the tube feet.

5. Locate the tube feet by turning the sea star over. The many tube feet are ingrooves that run down the center of each arm. Touch the tube feet; you willnotice that they cling to your finger. Each tube foot looks like a tiny plunger.Put the sea star back in the pan of water, with the tube feet facing down.Notice the clinging and pulling action of the tube feet used in locomotion.Make a sketch of a tube foot and describe its function.

6. Now place the sea star ventral side up in the pan of seawater. Make a sketchof the sea star that shows its ventral side. Describe the motion of the tubefeet. Can the sea star turn itself over? Which arms does it use to turn over?Record your observations in a copy of Table 11-1 in your notebook.

Adaptations of Sea Stars

TABLE 11-1 SEA STAR STRUCTURES AND FUNCTIONS

Sea Star Observations Structure Function Behavior

Dorsal Side

Ventral Side

7. How does the sea star feed? Look for the mouth in the center of the sea staron its ventral side. The mouth is too small to ingest a whole clam. Instead,the sea star pushes its thin, membranous stomach out through its mouthand into the clam’s shell, where it digests the food externally. Open up amussel or clam shell and put it in a pan of seawater. Place a sea star that hasnot been fed for a few days next to the clam. Record your observations.

8. How does a sea star open up a clam? Put your hand underwater and place asea star on top of it. Gently try to pull the sea star off your hand. Notice howit clings to your skin. The tube feet, with their suction disks, generate apulling force. When the arms of a sea star are draped over the two shells of aclam, hundreds of tube feet pull the shells in opposite directions. The adduc-tor muscles in the clam become fatigued, causing the shells to open.

OBSERVATIONS AND ANALYSES

1. How does a sea star move?

2. How does the sea star ingest and digest food?

3. Compare the “skeleton” of a mollusk with that of an echinoderm.

Echinoderms 273

Answer the following questions on a separate sheet of paper.

Vocabulary

The following list contains all the boldface terms in this chapter.

ampulla, Aristotle’s lantern, brittle stars, crinoids, echinoderms,endoskeleton, eyespots, feather stars, sand dollar, sea cucumbers,sea lilies, sea stars, sea urchin, sieve plate, skin gills, tube feet,water vascular system

Fill In

Use one of the vocabulary terms listed above to complete each sentence.

1. Delicate echinoderms found on the seafloor are the ____________________.

2. The ____________________ uses its short spines to burrow in the sand.

3. Water enters a sea star through its madreporite, or ____________________.

4. The ____________________ are the most ancient group of sessile echino-derms.

5. In sea stars, the clinging and pulling of muscles in ____________________

allows movement.

Think and Write

Use the information in this chapter to respond to these items.

6. Describe what happens if a sea star loses one of its arms.

7. What functions do spines serve in the sea urchins and sanddollars?

8. Compare and contrast the lifestyles of sea lilies and featherstars.

Inquiry

Base your answers to questions 9 through 12 on the results of the experi-ment described below and on your knowledge of marine science.

A marine biology student hypothesized that a brittle star wouldhave a slower turnover response than an Atlantic sea star. To testthis idea, he placed the two species of echinoderms upside down

Chapter 11 Review


in separate containers of seawater under the same experimentalconditions. The time it took for each animal to turn over (in eachof six trials) is shown in the table below.

Brittle Star Atlantic Sea Star

Trial Turnover Response Time Trial Turnover Response Time (minutes) (minutes)

1 0.15 1 6.0

2 0.17 2 10.0

3 0.33 3 2.0

4 0.25 4 1.75

5 0.23 5 2.50

6 0.15 6 2.0

Average 0.21 Average 4.04

9. Which part of the scientific method is represented by the datain the table? a. hypothesis b. materials c. resultsd. conclusion

10. Which is an accurate statement regarding the data in thetable? a. The data support the hypothesis. b. Thehypothesis is not supported by the data. c. The averageturnover response for the brittle star is 21 seconds. d. Theturnover response was recorded in seconds, not minutes.

11. A tentative conclusion that can be drawn from the data in thetable is that a. the brittle star moves more quickly than theAtlantic sea star b. the Atlantic sea star moves more quicklythan the brittle star c. turnover response in echinodermscannot be measured in minutes d. there is no significantdifference in turnover response time between the sea star andthe brittle star.

12. Which of the following suggests the best way to verify theresults of this experiment? a. Perform the experiment again,but with fewer trials. b. Perform the experiment again, butwith more trials. c. Add food to give each animal anincentive for movement. d. Use brittle stars only in bothcontainers of seawater.

Echinoderms 275

Multiple Choice

Choose the response that best completes the sentence or answers thequestion.

13. The small ciliated projections thatenable breathing in this animal arecalleda. spinesb. skin gillsc. ampullaed. eyespots.

14. You notice that a sea star in an aquarium has one very shortarm. The best explanation for this is that a. its growthhormones have been suppressed b. the appendage was lostand is regenerating c. its tube feet are not functioningd. the arm is not really needed.

15. The side of a sea star on which its sieve plate is found is thea. dorsal b. ventral c. anterior d. posterior.

16. What prevents a sea star from falling off the side of anaquarium tank? a. clinging action of its tube feetb. suction by its mouth c. adhesive properties of its spinesd. water pressure

17. The symmetry of echinoderms is referred to as a. bilateralb. radial c. spiral d. unilateral.

18. A sea star can open up a clam because of the functioning of itsa. tube feet b. spines c. stomach d. madreporite.

19. The crown-of-thorns sea star is considered a pest because ita. destroys coral reefs b. consumes bivalve mollusksc. is harmful to humans d. is harmful to fish.

20. The function of the water vascular system in the sea star is toenable a. locomotion b. digestion c. sensitivityd. respiration.

21. Which of these echinoderms moves most rapidly on theseafloor? a. sea star b. brittle star c. sea lilyd. sea urchin


22. The echinoderm that uses both its spines and its tube feet tomove is the a. sea urchin b. brittle star c. feather stard. sea star.

23. Sea urchins scrape the algae from rock surfaces with aspecialized mouthpart called the a. sieve plateb. madreporite c. Aristotle’s lantern d. skin gill.

24. The echinoderm that differs from all others in that it lacksan endoskeleton, and only retains small bony pieces in itsskin, is the a. sand dollar b. sea lily c. brittle stard. sea cucumber.

Research/Activity

■ Observe sea stars moving in an aquarium. Examine the under-side (ventral surface) of the sea stars as they move along thesides of the tank. Describe the motion of their tube feet andexplain how sea stars use their arms to grip surfaces and turnover.

■ Use the Internet to get an update on the sea cucumber harvestin the Galápagos Islands or to research the latest findings on thedamage done to coral reefs by the crown-of-thorns sea star.Write a report and present your findings to the class.

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11 echinoderms - washingtonville central school · pdf fileidentify the important...

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