Reading Essentials for Biology Glencoe (794133), страница 75
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The cilia that line the gills pushREADING ESSENTIALS7. What connects the twoshells of a bivalve?________________________________________________________________________Chapter 27329NameDateClassSection27.1Mollusks, continuedfood particles to the mouth. The cilia also sort out food fromlarge particles and sediment. These and other items that arerejected are carried to the bivalve’s mantle. These rejected particles are pushed out. Rejected particles also may be carried to thefoot where they are eliminated from the animal’s body.8. What body structure docephalopods have inplace of a foot?________________________________________________________________________Cephalopoda means head-footed. Cephalopods live in oceans.Octopus, squid, cuttlefish, and the chambered nautilus arecephalopods.
The only cephalopod that has a shell is the chambered nautilus. Some species, such as the cuttlefish, have reducedinternal shells, but they do not have external shells. Scientistsconsider the cephalopods to have the most complex structure.Scientists also think the cephalopods are the most recentlyevolved mollusk.In the cephalopods, the foot has evolved into tentacles withsuckers, hooks, or sticky adhesive structures. Cephalopods swimor walk over the ocean floor to catch their food. They catch foodin their tentacles, bring it to their mouths, and bite it with strong,beaklike jaws.
Like many other mollusks, they have radulas. Theyuse their radulas to tear food and pull it into their mouths.Cephalopods, like bivalves, have siphons that push water out.They can expel water in any direction, and they can move quicklyby jet propulsion. Using the force of expelled water, squids cantravel up to 20 m per second. Squids and octopuses use jetpropulsion to escape danger. They also can release a dark fluid, or“ink,” that darkens the water around them. This “ink” helps toconfuse their predators because the cephalopod can no longer beeasily seen.◗ After You ReadMini Glossaryclosed circulatory system: blood moves throughthe body, but it is enclosed entirely in aseries of blood vesselsopen circulatory system: blood moves throughvessels and also into open spaces around thebody organsmantle (MAN tuhl): a membrane that surroundsthe internal organs of the molluskradula (RA juh luh): a tonguelike organ withrows of teethnephridia (nih FRIH dee uh): organs that removemetabolic wastes from an animal’s body330Chapter 27READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Which mollusks belong to the class Cephalopoda?NameDateClassSection27.1Mollusks, continued1.
Read the terms and definitions in the Mini Glossary on page 330. Then on the lines below,explain how each term functions in a mollusk.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2.
Use the text and the diagram below to identify mollusks according to their classes and list anidentifying characteristic of each mollusk.MolluskClassIdentifyingCharacteristicsSnailCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.SquidClamSea slugOysterOctopusVisit the Glencoe Science Web site at science.glencoe.comto find your biology book and learn more about mollusks.READING ESSENTIALSChapter 27331NameDateClassSection27.2 Segmented WormsSC.G.1.4.1 The student knows of the great diversity and interdependence of living things. Also covers SC.F.1.4.2, SC.F.2.4.1◗ Before You ReadHave you ever watched a segmented worm crawl into the soil? Was it burrowing away from you forsafety or for other reasons? Why do you think worms are segmented? Why do they burrow into theground? Write your thoughts on the lines below.______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentify MainIdeas Highlight the mainpoint in each paragraph.
Readthe main points carefully andrestate each in your ownwords. Use your words to create an outline of this section.1. What is the basic bodyplan of a segmentedworm?________________________________________________________________________332Chapter 27Segmented worms include leeches, bristleworms, and earthworms. They are classified in the phylum Annelida. Segmentedworms are bilaterally symmetrical, the same on both sides.
Likemollusks and other animals you have studied, they have a coelom.Segmented worms also have two openings on their bodies. Oneopening is for taking in food and the other opening is for releasing wastes. Some segmented worms have a larval stage similar tolarval stages of certain mollusks. This similar larval stage suggeststhat mollusks and segmented worms may have a common ancestor.The basic body plan of a segmented worm is a tube within atube. The internal tube, which is suspended within the coelom, isthe digestive tract. The worm takes food in through the mouth,which is the opening in the front, or anterior, end of its body.The worm releases its waste through the anus, an opening at theback, or posterior, end of its body.Most segmented worms have tiny bristles called setae (SEE tee)on each segment. These bristles help the worms move.
Using thesetae, the worm anchors its body in the soil. Each segment thenhelps move the animal along its path.You can find segmented worms almost everywhere except inthe frozen soil of the polar regions and in the dry sand and soil ofthe deserts. There are about 15 000 species of segmented wormsthat live in soil, freshwater, and saltwater. Earthworms are just oneof the many species of segmented worms that live on our planet.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is a segmented worm?NameDateClassSection27.2Segmented Worms, continuedWhy is segmentation important?The body of a segmented worm is cylindrical, long and round.The body is divided into ringed segments.
The giant earthwormof Australia can grow to more than 3 m long and the ringed segments are easily seen. The segmentation on the outside of a wormis repeated inside the worm. Internally, each segment is separatedfrom others by a body partition. Each segment has its own muscles. By using these separated muscles, a worm can shorten andlengthen its body to move.Segmentation also allows for specialization of body tissues.Groups of segments work together for a particular purpose orfunction.
Certain segments have adaptations or modifications forsensing surroundings and for reproduction.2. What are the twoprimary advantages ofsegmentation?________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What kind of nervous system does a segmentedworm have?Segmented worms have simple nervous systems.
Organs in thefront segments are able to sense the environment. Other sensoryorgans in the front segments detect light. Some segmented wormshave eyes with lenses and retinas. Some species have a brain inthe front segment. Nerve cords connect the brain to nerve centersthat are found in each segment of the worm. These nerve centersare called ganglia.What type of circulatory system do segmentedworms have?Segmented worms have a closed circulatory system. As youlearned in the first section of this chapter, a closed circulatory system means that blood flows through closed vessels. Blood thatcarries oxygen to the body cells also carries carbon dioxide awayfrom body cells. In a segmented worm, blood flows to all parts ofthe worm’s body.
Segmented worms must live in water or in wetareas on land because they exchange oxygen and carbon dioxidedirectly through their moist skin.Do segmented worms have a digestive system?Segmented worms have a complete internal digestive tract thatruns from the front of the worm to the end of the worm. Whena worm eats, food and soil that go into the mouth eventually passinto the gizzard.
A muscular sac and hard particles in the gizzardhelp grind the soil and the food before they are passed into theREADING ESSENTIALSChapter 27333NameDateClassSectionSegmented Worms, continued3. What is the function ofthe gizzard?________________________________________________intestine. Material that cannot be digested and solid wastes passout of the worm’s body through the anus.
The anus is the opening in the worm’s body that is located at the posterior end. Likemollusks, segmented worms also have nephridia as shown in theillustration below. In a segmented worm, there are two nephridiain almost every segment. The nephridia collect wastes and movethem through the coelom and out of the worm’s body.________________________A MouthAn earthworm takessoil into its mouth,the beginning of thedigestive tract.B GizzardThe gizzard grinds the organic matter,or food, into small pieces so that thenutrients in the food can be absorbedas it passes through the intestine.Undigested food and any remaining soilare eliminated through the anus.C SetaeAn earthworm alternatelycontracts sets of longitudinaland circular muscles to move.First it contracts its longitudinalmuscles on several segments,which bunch up.
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