Sponges and Cnidarians

Reading PreviewKey Concepts• What are the main characteristics

of sponges?

• What are the main characteristics

of cnidarians?

• Why are coral reefs important?

Key Terms• larva • cnidarian • polyp

• medusa • colony • coral reef

'@Target Reading SkillComparing and ContrastingAs you read, compare and contrast

sponges and cnidarians by

completing a table like this one.

Sponges and Cnidarians

Feature

Body

structure

Celt typethat trapstood

Method(s)of reprosduction

Sponge Cnidarian

Hollow bagWith pores

zoneDiscover Activity

How Do Natural and SyntheticSponges Compare?1. Examine a natural sponge, and then use a hand lens or a

microscope to take a closer look. Look carefully at the holes inthe sponge. Draw what you see through the lens.

Cut out a small piece of sponge and examine it Witha hand lens, Draw what you see.

3. Repeat Steps 1 and 2 with a synthetic kitchen sponge.

Think It OverObserving What are three ways a natural and a syntheticsponge are similar? What are three ways they are different?

Eagerly but carefully, you and the others in your group put onscuba gear as you prepare to dive into the ocean. Over the sideof the boat you go. As you descend through the water, you seemany kinds of fishes. When you get to the bottom, you noticeother organisms, too. Some are as strange as creatures from ascience fiction movie. A few of these unusual organisms may be

invertebrate animals called sponges.

Sponges don't look or act like most animals you know Infact, they are so different that for a long time, people thoughtthat sponges were plants. Like plants, adult sponges stay Inone place. But unlike most plants, sponges take food intotheir bodies.

SpongesSponges live all over the world—-mostly inoceans, but also in freshwater rivers and lakes.

Adult sponges are attached to hard surfacesunderwater Water currents carry food andoxygen to them and take away their waqteproducts. Water currents also play a role intheir reproduction and help transport theiryoung to new places to live.

Diver investigating abarrel sponge

Chapter 9 303

Go onlineactive art\

For: Structure of a Sponge activityVisit: PHSchool@comWeb Code: cep-2013

FIGURE 11

Structure of a Sponge

Body Structure Sponges are invertebrate animals

usually have no body symmetry and never have tissuesorgans. A sponge looks something like a hollow bag withlarge opening at one end and many tiny pores covering itsface. In fact, the name of the phylum to which sponges

belong—phylum Porifera—means "having pores."

Look at Figure I l. A sponge's body has different kinds

and structures for different functions. For example, most

have spikes. The network of spikes throughout the sponge sups

ports its soft body, keeping it upright in the water. The spikes

help a sponge defend itself against an animal that might eat

which is called a predator. The spikes can be as sharp as needles

Even so, some fish eat sponges.

Structures surrounding the central cavity ofa sponge are adapted for different functions.Interpreting Diagrams Which kind of cell inthe sponge digests and distributes food?

Collar CellThe collar cells have whiplikestructures that beat back andforth, moving water throughthe sponge and trapping food.

SpikeThin spikes form arigid frame that helpssupport and protectthe sponge's body.

Jelly-like CellAmong the spikes are jelly-likecells that digest and distributefood, remove wastes, and formsperm or egg cells,

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PoreWater moves into the centralcavity through small pores allover the sponge's body. It exits

from a large hole at the top.

FIGURE 12

Reproduction of a SpongeThe sexual reproduction of sponges

involves a larval stage that moves.

Adult sponges stay in one place.

The larva

settles on a

hard surface

and develops

into anadultsponge.

O Water currentscarry the larvaaway.

An adult spongereleases sperm cells.

Obtaining Food and Oxygen A sponge eats tiny single-celled organisms. The sponge filters these organisms from the

water moving through it. The collar cells that line the central

cavity trap the tiny organisms. Jelly-like cells inside the sponge

then digest, or break down, the food. Larger sponges can filter

thousands of liters of water per day!

A sponge gets its oxygen from water, too. After the water

moves through a sponge's pores, it passes over cells inside the

sponge. Oxygen in the water then moves into the sponge's cells.

Reproduction Sponges reproduce both asexually and sexually.

Budding is one form of asexual reproduction in sponges. In bud-

ding, small new sponges grow from the sides of an adult sponge.

Eventually, the buds break free and begin life on their own.

Sponges reproduce sexually, too, but they do not have sepa-

rate sexes. A sponge produces both sperm cells and egg cells. The

sperm cells are released into the water. They enter another

sponge and fertilize its eggs, as shown in Figure 12. After fertili-

zation, a larva develops. A larva (plural larvae) is an immature

form of an animal that looks very different from the adult.

Reading What is a larva?Checkpoint

@The sperm enter another

sponge. A sperm cell

fertilizes an egg cell.

O A larvadevelops.

Mathski I I

Calculating a RateTo calculate the rate of waterflow in a sponge, divide thevolume of water that thesponge filters by the time ittakes the water to passthrough the sponge.

Volume of waterFlow rate

Time

For example, a marble-sizedsponge filters 15.6 liters ofwater in a day. How manyliters does it fitter per hour?

15.6 L = 0.65 Uh24 h

Practice Problem In 4 days,a sponge filters 1,200 L.What is its rate of water flowper day?

Chapter 9 305

LabzoneConsumer LabData Table

Soak It Up!ProblemWhich sponge absorbs the most water?

Skills Focusobserving, predicting, communicating

Materials• damp piece of • balance

cellulose sponge • large bowl of tap• damp piece of natural water

sponge • graduated cylinder• damp piece of foam • beaker

sponge • paper towel

Procedure O1. Copy the data table on a separate sheet.

2. Examine the size of the pores in eachsponge. Record your observations.

3. Make a prediction about which sponge willabsorb the most water. Record your predic-tion and give a reason.

4. Place a damp piece of cellulose sponge on abalance and measure its mass. Record themass in the data table. Remove the spongefrom the balance.

5. Repeat Step 4 with the natural sponge andthen the foam sponge.

6. Submerge the cellulose sponge in a bowl ofwater. Squeeze it several times to remove allair bubbles. Release the sponge and let itabsorb water. Then remove the sponge andplace it in the beaker

7. Squeeze out as much water as possible fromthe sponge into the beaker. (Hint: Squeezeand twist the sponge until no more drops ofwater come out.)

8. Pour the water from the beaker into thegraduated cylinder. Measure the volume ofwater and record the volume in the datatab*e. Pour the water from the graduatedcylinder back into the bowl. Dry the gradu-ated cylinder and beaker with a paper towel.

Type of Sponge

Cellulose

Natural

Foam

Volume ofMass ofSize of Absorbed

Damp Pores Totalsponge

(mL)Per G(rnL/g)

9. Repeat Steps 6—8 using the natural spongeand then the foam sponge. When you arefinished, squeeze all the water from yoursponges, and return them to your teacher.

10. Calculate the volume of water absorbed pergram of sponge, using this formula:

Volume of absorbed water _ Volume absorbed

Mass of damp sponge per gram

Analyze and Conclude1. Observing Which sponge absorbed the most

water per gram of sponge? The least? Wasyour prediction confirmed?

2. Drawing Conclusions What can you con-clude about the relationship between poresize and the ability of the sponge to absorbwater?

3. Predicting How would the volume ofabsorbed water change if each of thesponges had twice the mass of the spongesyou studied? Explain.

4. Communicating Natural sponges can costmore than cellulose and foam sponges. Con-

sider that information and the results of your

investigation. Which sponge would you rec-ommend to consumers for absorbing waterspills? Explain your choice.

Design an ExperimentDesign an experiment to test the prediction you

made in Question 3 above, Write your hypothesis

as an "If then , " statement, Obtain your

teacher's permission before carrying out your

investigation.

Cnidariansother animals you might notice on an underwater dive

Jre lelftfashes, corals, and sea anemones. These animals arecnidarians (nv DEHR ee unz), invertebrates that have stinging

and take food into a central body cavity. Cnidarians usestinging cells to capture food and defend themselves.

Body Structure Cnidarians have two different body plans,pu can see in Figure 13. Notice that one form looks

s,mething like a vase and the other form looks like an upside-bowl. Both body plans have radial symmetry, a central

hollow cavity, and tentacles that contain stinging cells.The vase-shaped body plan is called a polyp (PAHL ip).

The sea anemone you see in Figure 13 is a polyp. A polyp'smouth opens at the top and its tentacles spread out fromaround the mouth. Most polyps are adapted for a life attached

to an underwater surface.

The bowl-shaped body plan is called a

Try This Activityzone

Hydra Doing?Put a drop of water

containing hydras in

a smatf unbreakable bowl

or petri dish. Allow it to sit

for about 15 minutes.

2. Use a hand lens to examine

the hydras as they swim.

Then gently touch the

tentacles of a hydra with

the end of a toothpick.

Watch what happens.

3. Return the hydras to your

teacher. Wash your hands.

Classifying Is a hydra a polyp

or a medusa? Describe its

method of movement.medusa (muh DOOsuh), The jellyfish you see in Figure 13 is a medusa. A medusa,

unlike a polyp, is adapted for a swimming life. Nledusas have

mouths that open downward and tentacles that trail down.Some cnidarians go through both a polyp stage and a medusa

stage during their lives. Others are either polyps or medusas for

their entire lives.

FIGURE 13

Cnidarian Body PlansCredanans have two basic body forms, thevase-snaped polyp and the bowl-shaped medusa.Con-tparing and Contrasting Contrast the location

of toe mouth in the polyp and the medusa.

Jellyfish

FIGURE 14

Cnidarian Attack!A stinging cell fires when its triggerbrushes against prey, such as a fish.

FIGURE 15

Movement of a MedusaA medusa's nerve net signals thetop part of the medusa's body tocontract and relax. As the top of itsbody contracts, the medusa movesupward through the water.

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Trigger

Stinging Cell at RestSpines

Stinging Cell After Firing

Obtaining Food Both polyps and medusas obtain foodin

the same way. Cnidarians use stinging cells to catch the ani

they eat, which are called prey. You can see a stinging cellFigure 14. The cell contains a threadlike structure, which hasmany sharp spines. When the stinging cell touches prey, this

threadlike structure explodes out of the cell and into the prey.

Some stinging cells also release venom into the prey. theprey becomes helpless, the cnidarian uses its tentacles to pull theprey into its mouth. From there, the prey passes into a hollow

central body cavity, where it is digested. Undigested foodisexpelled through the mouth.

Movement Unlike adult sponges, many cnidarians can

move to escape danger and to obtain food. Some cnidarians

have muscle-like tissues that allow them to move in different

ways. Jellyfishes swim through the water, and hydras turn slow

somersaults. Sea anemones stretch out, shrink down, bend

slowly from side to side, and often move slowly from place toplace. A cnidarian's movements are directed by nerve cellsthat are spread out like a basketball net. This nerve nethelps a cnidarian respond quickly to danger andto nearby food.

Adult medusas reproduce sexually

by releasing egg and sperm cells.

Spermmedusa

A sperm cell fertilizes

an egg cell.

Eggs

Femalemedusa

O Each "disc"matures intoan adultmedusa.

Polyp

The polyp reproducesasexually. Many disc-shapedstructures break awayfrom the polyp.

Reproduction Cnidarians reproduce both asexually and

For polyps such as hydras, corals, and sea anemones,

ba&åing is the most common form of asexual reproduction.

Amazinév, some polyps just pull apart, forming two new pol-

Both kinds of asexual reproduction allow the numbers of

to increxse rapidly in a short time.

reproduction in cnidarians occurs in a variety of

Some specres of cnidarians both sexes within one

iduai. In others, the sexes are separate Many

cnidarians life OVIes, or a sequence of different stages of

dnelopment. In Figure 16, you can see the life Cycle of a moon

uhiv-h invobes both asexual and sexual reproduction.

What are two examples of asexual reproductionseen in polyps?

O A swimminglarva develops.

O The larvaattaches to ahard surfaceand developsinto a polyp.

FIGURE 16

Life Cycle of a JellyfishThe life cycle of a moon jelly hasboth a polyp and a medusa stage,and both asexual reproductionand sexual reproduction.Interpreting Diagrams Whichform of the moon jelly (polyp ormedusa) shows a form of asexualreproduction ? Explain.

Chapter 9 • 309

J.

v, Coral polyps Coral reef

FIGURE 17

Coral ReefThe massive reef surrounding thistropical island is made from theskeletal remains of the tinycnidarians called coral (inset).

DJ S oueryCHANNEL

S OOLSponges.Cnidarians, andWorms

Video Field Trip

mWéOVAS$eSsment

310

Life in a ColonyMany cnidarians spend their lives as individuals, but not all.

Some species of cnidarians live in a colony, a group of manv

individual animals. Stony corals and the Portuguese man-of.

war are two examples of colonies of cnidarians.

Stony Corals Coral reefs are found in warm, shallow ocean

waters, mainly in tropical regions of the world. They may seem

to be made of stone, but are not. A coral reef is built by cnidar.

ians. At the beginning of its life, a coral polyp attaches to a solid

surface. A broken shell, a sunken ship, or a rock will do just

fine. After attaching to the solid surface, the coral polyp pro.

duces a hard, stony skeleton around its soft body.The coral polyp reproduces asexually, and then its offspring

reproduce asexually, too. Over time, that polyp may give rise tothousands more, each with a hard skeleton. When the polyps

die, their skeletons remain behind. Over thousands of years, as

live corals add their skeletons to those that have died, rocklik

reefs grow up from the sea floor. The top layer of the reef iscovered with hundreds of thousands of still-living coral polyp.

Coral reefs are home to more species of fishes and

invertebrates than any other environment on Earth. Hun-

dreds of sponge species live among the corals, constantly file

tering water through their bodies. Worms burrow into the

coral reef. Giant clams lie with their huge shells slightly open,

Shrimp and crabs edge out of hiding places below the corals,

At night, bright blue damselfish settle into pockets in the coral

At dawn and dusk, sea turtles, sea snakes, and sharks all visit

the reef, hunting for prey. These living things interact in

complex ways, creating a rich and beautiful environment,

roe •

portuguese Man-of-War Sometimes the assouation ofLdiiidual animals in a colony is so tight that the colonv actsEke a single animal. The Portuguese man•f-war contains asmany as 1,000 indixåduals that function together as ene unit.

At the top of the Portuguese is a gas-tilledchamber that allows the colonv to float on the surface of theocean. Various ponvs with different functions below.

Some poly'S catch prey for the colonv mth stinging cellsOthers digest the prey. Still other ponvs atv adapted torreproduction.

Reoding What are two examples of colonies ofChækpoint cnidarians?

Section 3 Assessment

@Target Reading Skill Comparing and 3. a. identåymg a cotat

Contrasting Use table to quit a partner about

how sponges and cnidarians trap food. How

do therr methods for trapping toed differ?

Reviewing Key Conceptst. a. Describing are the

of a sponge?

b. Comparing and Contrasting How are the Gilsof a sponge alike? How are thev ditÄQrcnt?

2. a. Identifying is one of cell that allcnidarians have?

b. Sequencing steps arv m how a

cnidarian obtatns food?

C. Making Judgments toprotect coral veers?

MathPractice

4. a Rate A very large canfitter 1,500 liters of water in amuch water can fitter pet

1

c. Inferring mtght a cnidarian protect itself?

Chapter 9

Science andSociet

Coral Reefs in DangerCoral reefs off the coasts of many nations are

in danger. Although coral reefs are as hard as

rocks, the coral animals themselves are quite

delicate. Recreational divers can damage the

fragile reefs. Is it possible to protect the reefs

while still allowing divers to explore them?

The IssuesWhat's the Harm in Diving?More than 1.5 million recreational divers live in the

United States. writh so many divers it is hard to guarantee

that no harm will occur to coral reefs. Divers can cause

significant damage by standing on or even touching these

fragile reefs. Harm to the reefs is even more likely to occur

when divers collect coral for their own enjoyment or

to sell for profit. You can see brightly colored coral

from the sea in jewelry and in decorations.

Should Reefs Be Further Protected?The United States government has passed laws making it

)DIVERSSUPPLY SHOP

Piff

Diving supports local businesses

illegal, under most circumstances, to remove coral from the sea.

Because a few divers break these laws, some people want to ban

diving altogether. However, many divers say it's unfair to ban divingjust because of a few lawbreakers.

Many divers consider coral reefs the most exciting and beautifulplaces in the ocean to explore. As divers and other people visit andlearn more about these delicate coral reefs, they increase others'awareness of them. Public awareness may be the best way to ensurethat these rich environments are protected.

More Than a Diving IssueCoral reefs are major tourist attractions that bring money andjobs to people in local communities. If diving were banned, localbusinesses would suffer significantly. Also, although divers can harmcoral reefs, other human activities that result in ocean pollution, oilspills, and illegal fishing can also cause harm. In addition, naturalevents, such as tropicaJ storms, changes in sea level, and changes in seatemperature, can also damage the fragile reefs.

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