Reading Essentials for Biology Glencoe (794133), страница 82
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The pharynx is located behind the mouth. Manychordates have these pouches only during their embryonic stages.In chordates that live in the water, pharyngeal pouches developopenings called gill slits. The gill slits filter food and gas exchangeoccurs as water flows through them. In chordates that live onland, the pharyngeal pouches develop into other structures.What is a postanal tail?All chordates have a postanal tail. In some chordates the taildisappears during the early developmental stages.
For example,during the early development of the human embryo, the embryohas a postanal tail. The tail disappears as development continues.In most animals that have tails, the digestive system extends to thetip of the tail. This is where the anus is located. In chordates,however, the tail extends beyond the anus.360Chapter 29READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is a dorsal hollow nerve cord?NotochordNameDateClassSection29.2Invertebrate Chordates, continuedMuscle blocks help the tail move.
Muscle blocks are modifiedbody segments that consist of stacked layers of muscle. Muscleblocks are held in place by the notochord. The notochord givesthe muscles a firm structure to pull against. As a result, chordatesgenerally have stronger muscles than members of other phyla.2. Analyze Why do chordates have stronger muscles than members ofother phyla?How do homeotic genes control development?________________________Homeotic genes outline body organization.
They also directthe development of tissues and organs in the embryo. Scientistshave studied chordate homeotic genes. These studies have helpedscientists understand the development of chordates and the relationship between invertebrate and vertebrate chordates.________________________________________________Diversity of Invertebrate ChordatesThe invertebrate chordates belong to two subphyla in the phylum chordata. One subphylum is called Urochordata. Tunicates(TEW nuh kaytz), or sea squirts, belong to this subphylum.
Theother subphylum is called Cephalochordata. Lancelets belong to this subphylum.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are tunicates?Tunicates are members of the subphylum Urochordata. Adult tunicates, or seasquirts, do not seem to have any of thecommon chordate features.
In the larvalstage, a sea squirt has a tail that makes itlook similar to a tadpole. Sea squirt larvaedo not feed. After they hatch, the larvaeare free swimming. They soon settle andattach themselves with a sucker to boats,rocks, and the ocean floor. Many adultsea squirts secrete a tunic, a tough covering, or sac, made of cellulose. It surroundstheir bodies. The figure at right showsthe parts of a tunicate.Sometimes tunicates form a group ora colony.
A colony of tunicates sometimes secretes one big tunic that will haveone opening to the outside.WaterMouthGill slitsAnusReproductiveorgansIntestineEsophagusStomachTunicREADING ESSENTIALSChapter 29361NameDateClassSection29.2Invertebrate Chordates, continued________________________The gill slits in adult sea squirts show that they are chordates.The adult animals are small, tube-shaped animals. They may bemicroscopic in size, or they may be several centimeters long. Ifyou take an adult tunicate from its home, it may squirt water atyou. This is how the tunicate got the name sea squirt.________________________What are lancelets?3. How do we know thatsea squirts are chordates?________________________Lancelets are similar to fishes.
They are small, common animals that live in the sea. Lancelets belong to the subphylumCephalochordata. Lancelets spend most of their time buried inthe sand with only their heads sticking out. Like tunicates,lancelets are filter feeders. Unlike tunicates, lancelets keep alltheir chordate features for their entire lives.Although lancelets look similar to fish, there are some differences. Lancelets have only one layer of skin. They do not havepigment or color.
They do not have scales or a distinct head.Lancelets can sense light because they have light-sensitive cells onOral hood with tentaclesMouthNotochordPostanaltailGill slitsin pharynxIntestineMuscle blocksAnus4. Why do sea squirts andlancelets have an incomplete fossil record?________________________________________________________________________362Chapter 29the anterior or front end of their bodies. They have a mouth thatis surrounded by sensory tentacles. Lancelets have a hood thatcovers the mouth and these tentacles.Origins of Invertebrate ChordatesSea squirts and lancelets do not have bones, shells, or otherhard parts.
Because they do not have hard parts, their fossilrecord is incomplete. Biologists do not know exactly where seasquirts and lancelets fit in the phylogeny of chordates.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Dorsal hollownerve cordNameDateClassSection29.2Invertebrate Chordates, continuedIt is possible that echinoderms, invertebrate chordates, andvertebrates came from ancestral, stationary animals that caughtfood in their tentacles. Modern vertebrates may have come fromfree-swimming larval stages of ancestral invertebrate chordates.Scientists have recently found fossil forms of organisms that aresimilar to present-day lancelets. These fossil forms are in rocksthat are 550 million years old.
These fossils tell us that invertebrate chordates probably existed before vertebrate chordates.◗ After You ReadMini Glossarydorsal hollow nerve cord: develops from a plateof ectoderm that rolls into a hollow tube. Inmost adult chordates, this develops into thespinal cord.notochord: a long, semirigid rodlike structurelocated between the dorsal hollow nervecord and the digestive systempharyngeal pouches: paired openings located inthe pharynx, behind the mouth1. Read the terms and their definitions in the Mini Glossary above. Use the space below toexplain the importance of the dorsal hollow nerve cord.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.____________________________________________________________________________________2. In the diagram, fill in seven characteristics that all chordates have.ChordateCharacteristicsVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about invertebrate chordates.READING ESSENTIALSChapter 29363NameDateClassSection30.1 FishesSC.F.1.4.2 The student knows that body structures are uniquely designed and adapted for their function.
SC.G.1.4.1The student knows of the great diversity and interdependence of living things. Also covers SC.F.1.4.7, SC.F.2.4.1◗ Before You ReadWhy do you think fish swim so easily and effortlessly in the water? On dry land, they cannot moveefficiently, and they quickly die. On the lines below, explain why you think fish have adapted so wellto their watery environment but have never adapted to a land environment.______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnSummarizeHighlight each of the questionheadings about fishes.
Afteryou have read the section,write the answer to eachquestion in your own words.Fishes are vertebrates. This means that they have backbones.Fishes are members of the phylum Chordata. There are threesubphyla in Chordata. The Urochordata include the tunicates orsea squirts. The Cephalochordata include the lancelets. Vertebrataare the vertebrates. Fishes, amphibians, reptiles, birds, and mammals are all vertebrates. Remember that vertebrates are chordates.All chordates have a notochord, pharyngeal pouches, a postanaltail, and a dorsal hollow nerve cord.
In vertebrates the notochordthat is found in the embryo becomes a backbone in the adult animal. All vertebrates are bilaterally symmetrical. They are coelomates and have endoskeletons. Their closed circulatory systemsflow blood through the body in enclosed blood vessels. Vertebrateshave complex brains, sense organs, and efficient respiratory systems.How many classes of fishes are there?1.
What is the differencebetween Osteichthyesand Chondrichthyes?________________________________________________________________________________________________364Chapter 30There are four classes of fishes. Fishes that do not have jawsbelong to the superclass Agnatha. Agnatha means without jaws.Within the superclass Agnatha, there are two classes. Hagfishbelong to the class Myxini (mik SEE nee).
Lampreys belong to theclass Cephalaspidomorphi (se fa LAS pe do MOR fee). Sharks andrays, whose skeletons are made of cartilage, not bone, belong to theclass Chondrichthyes (kahn DRIHK theez). Fishes whose skeletons are made of cartilage are called cartilaginous fishes. Cartilageis a tough, flexible material. Fishes with bone skeletons belong tothe class called Osteichthyes (ahs tee IHK theez).READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is a fish?NameDateClassSection30.1Fishes, continuedFishes live in almost every kind of water environment on Earth.They live in salt water and freshwater. They live in shallow, warmwater, as well as deep, cold water that has very little or no light.How do fishes breathe?Fishes breathe by using their gills.
Notice in the figureto the right that gills are made up of filaments, which arefeathery, thread-like structures. These filaments containtiny blood vessels called capillaries. As a fish takes water inthrough its mouth, the water flows over the gills. The watergoes out through slits in the side of the fish.
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