23-1 CHAPTER 23 Chordates Chordates. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23-2 The Chordates:

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CHAPTER 23CHAPTER 23CHAPTER 23CHAPTER 23

ChordatesChordates ChordatesChordates

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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The Chordates: CharacteristicsThe Chordates: Characteristics

Structural Plan Structural Plan Name Name chordatachordata comes from the comes from the notochordnotochord 5 Hallmark chordate characteristics5 Hallmark chordate characteristics

Dorsal, tubular nerve cord (spinal cord)Dorsal, tubular nerve cord (spinal cord) Notochord (in some replaced by vertebrae)Notochord (in some replaced by vertebrae) Pharyngeal slits (gills)Pharyngeal slits (gills) Endostyle (aka - thyroid gland)Endostyle (aka - thyroid gland) Postanal tail (coccyx)Postanal tail (coccyx)


Characteristics of Chordates

Muscle segments

Mouth

Pharyngeal pouches

Anus Tail

Hollow nerve cord

Notochord


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Chordates share features with some Chordates share features with some invertebrates: invertebrates: Bilateral symmetryBilateral symmetry CoelomCoelom MetamerismMetamerism CephalizationCephalization Deuterostomes (like echinoderms)Deuterostomes (like echinoderms)

The Chordates: CharacteristicsThe Chordates: Characteristics


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Traditional and Cladistic Classification of the ChordatesTraditional and Cladistic Classification of the Chordates

Traditional classificationTraditional classification Protochordata Protochordata (no skull) are separated from (no skull) are separated from

Vertebrata Vertebrata that have a skull that have a skull Vertebrates may be divided into Vertebrates may be divided into Agnatha Agnatha

(jawless)(jawless) and and Gnathostomata (having jaws)Gnathostomata (having jaws) Gnathostomata Gnathostomata is subdivided into is subdivided into PiscesPisces

with fins and with fins and Tetrapoda,Tetrapoda, usually with two usually with two pair of limbspair of limbs


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Five Chordate HallmarksFive Chordate Hallmarks

Notochord Notochord Always found at some embryonic stage Always found at some embryonic stage First part of the endoskeleton to appear in First part of the endoskeleton to appear in

the embryothe embryo Serves as an axis for muscle attachmentServes as an axis for muscle attachment In protochordates (no skull) and jawless In protochordates (no skull) and jawless

vertebrates, vertebrates, Persists throughout life Persists throughout life


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In vertebratesIn vertebrates Series of cartilaginous or bony vertebrae Series of cartilaginous or bony vertebrae

form notochordform notochord In most vertebratesIn most vertebrates

Notochord displaced by vertebrae Notochord displaced by vertebrae Remnants may persist between or within Remnants may persist between or within

vertebraevertebrae



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Dorsal Tubular Nerve CordDorsal Tubular Nerve Cord Anterior end enlarges to form the brainAnterior end enlarges to form the brain Cord is produced in embryo by Cord is produced in embryo by

infolding of ectodermal cells on the infolding of ectodermal cells on the dorsal side of bodydorsal side of body



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Pharyngeal Pouches and SlitsPharyngeal Pouches and Slits Pharyngeal slits lead from pharyngeal cavity Pharyngeal slits lead from pharyngeal cavity

to the outsideto the outside Form by the inpocketing of the ectoderm and Form by the inpocketing of the ectoderm and

the evagination of endoderm of pharynxthe evagination of endoderm of pharynx In aquatic chordatesIn aquatic chordates

2 pockets break through to form pharyngeal slit2 pockets break through to form pharyngeal slit In amniotesIn amniotes

Pockets may not break through and only grooves Pockets may not break through and only grooves are formedare formed



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Phyla Chordata Cladogram


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In tetrapodsIn tetrapods Pharyngeal pouches give rise to a variety of Pharyngeal pouches give rise to a variety of

structures, including the Eustachian tube, middle structures, including the Eustachian tube, middle ear cavity, tonsils and parathyroid glandsear cavity, tonsils and parathyroid glands

Perforated pharynx functions as filter-Perforated pharynx functions as filter-feeding apparatus in protochordatesfeeding apparatus in protochordates

Fishes added a capillary network with thin Fishes added a capillary network with thin gas-permeable walls gas-permeable walls Led to evolution of gillsLed to evolution of gills



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Endostyle or Thyroid Gland Endostyle or Thyroid Gland Endostyle or its derivative, the thyroid Endostyle or its derivative, the thyroid

gland, found in all chordatesgland, found in all chordates Some cells in endostyle secrete Some cells in endostyle secrete

hormones similar to the thyroid gland hormones similar to the thyroid gland of adult lampreys and the remainder of of adult lampreys and the remainder of vertebratesvertebrates



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Postanal TailPostanal Tail Postanal tail, plus musculature, provided Postanal tail, plus musculature, provided

motility motility Efficiency increased in fishes but became Efficiency increased in fishes but became

smaller or vestigial in later lineagessmaller or vestigial in later lineages



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Subphylum Urochordata: TunicataSubphylum Urochordata: Tunicata

Diversity of UrochordataDiversity of Urochordata Approximately 3000 species of tunicates identifiedApproximately 3000 species of tunicates identified Occur in all seas and at all depthOccur in all seas and at all depth In most species, In most species, only the larvalonly the larval form bears all the form bears all the

chordate hallmarkschordate hallmarks Adults lose many of these charactersAdults lose many of these characters

During adult metamorphosisDuring adult metamorphosis Notochord and tail disappearNotochord and tail disappear Dorsal nerve cord is reducedDorsal nerve cord is reduced

UrochordataUrochordata include include All Tunicates including Sea SquirtsAll Tunicates including Sea Squirts


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AdultTunicate

Colony


Tunic

Heart

Pharynx with gill slits

Siphon to mouth

Siphon from anus

Anus

Intestine

Reproductive organs

Stomach

Adult

Nonvertebrate ChordatesTunicate


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Sea Squirt: Larval Stage has ALL 5 Chordate characteristics


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Tunicate: Illustrating Endostyle and Pharyngeal slits

(characteristics remainingIn adult tunicate)


Sea Squirt - Adult


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Subphylum CephalochordataSubphylum Cephalochordata

DiversityDiversity LanceletsLancelets

Slender, laterally flattened, translucent animals Slender, laterally flattened, translucent animals about 5–7 cm longabout 5–7 cm long

Live in sandy bottoms of coastal waters Live in sandy bottoms of coastal waters around the worldaround the world

Also known asAlso known as amphioxousamphioxous About 25 species of amphioxus are describedAbout 25 species of amphioxus are described

5 occur in North American coastal waters5 occur in North American coastal waters Many zoologists consider amphioxus a living Many zoologists consider amphioxus a living

descendant of ancestors that gave rise to both descendant of ancestors that gave rise to both cephalochordates and vertebratescephalochordates and vertebrates


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Amphioxus: Shows ALL 5

chordate characteristics

Post-anal

Tail


2 Amphioxus


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Subphylum Vertebrate (Craniata)Subphylum Vertebrate (Craniata)

Adaptations That Guided Vertebrate EvolutionAdaptations That Guided Vertebrate Evolution Earliest vertebrates Earliest vertebrates

Were substantially largerWere substantially larger Considerably more activeConsiderably more active Characterized by increased speed and mobilityCharacterized by increased speed and mobility

Higher activity level and size of vertebratesHigher activity level and size of vertebrates Requires structures specialized in the location, Requires structures specialized in the location,

capture, and digestion of food and adaptations capture, and digestion of food and adaptations designed to support a high metabolic ratedesigned to support a high metabolic rate


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Musculoskeletal ModificationsMusculoskeletal Modifications Most vertebrates possess Most vertebrates possess skeleton of skeleton of

cartilage or bonecartilage or bone Endoskeleton permits Endoskeleton permits almost unlimited body almost unlimited body

sizesize Endoskeleton allows Endoskeleton allows attachment of attachment of

segmented musclessegmented muscles Endoskeleton probably composed initially of Endoskeleton probably composed initially of

cartilagecartilage and later gave way to bone and later gave way to bone



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Vertebral ColumnAnd Head skeleton

Common in vertebrates

Spinal cord


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Endoskeleton of living hagfishes, Endoskeleton of living hagfishes, lampreys, sharks and their kin, and lampreys, sharks and their kin, and even some “bony” fishes, such as even some “bony” fishes, such as sturgeons, sturgeons, mostly composed of mostly composed of cartilagecartilage

Structural strength of bone is Structural strength of bone is superiorsuperior to cartilageto cartilage Makes it ideal for muscle attachment in Makes it ideal for muscle attachment in

areas of high mechanical stressareas of high mechanical stress Perhaps bone evolved, in part, as a Perhaps bone evolved, in part, as a

means of mineral regulation means of mineral regulation



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Some of the Some of the most primitive fishes,most primitive fishes, including including Ostracoderms and placoderms were partly Ostracoderms and placoderms were partly covered in a covered in a bony, dermal armorbony, dermal armor Modified in later fishes as Modified in later fishes as scalesscales

Most vertebrates are protected with Most vertebrates are protected with keratinized structures derived from the keratinized structures derived from the epidermisepidermis Reptilian scales, hair, feathers, claws, and hornsReptilian scales, hair, feathers, claws, and horns



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Physiology Physiology Modifications of digestive, respiratory, circulatory, Modifications of digestive, respiratory, circulatory,

and excretory systems to and excretory systems to meet increased metabolic meet increased metabolic demanddemand

To manage increased ingestion of foodTo manage increased ingestion of food Gut shifted from movement of food by ciliary Gut shifted from movement of food by ciliary

action to muscular actionaction to muscular action Accessory digestive glands, the liver and Accessory digestive glands, the liver and

pancreas, produced secretions that aided pancreas, produced secretions that aided digestiondigestion



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Transport of nutrients gases, and other Transport of nutrients gases, and other substances was enhanced by substances was enhanced by Ventral 3-chambered heartVentral 3-chambered heart

Sinus venosusSinus venosus AtriumAtrium VentricleVentricle

Included Included hemoglobin hemoglobin Vertebrates possess Vertebrates possess paired kidneyspaired kidneys to to

remove metabolic waste products and remove metabolic waste products and regulated body fluid compositionregulated body fluid composition



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New Head, Brain, and Sensory SystemsNew Head, Brain, and Sensory Systems Shift from filter feeding to Shift from filter feeding to active predationactive predation

Required new sensory, motor, and integrative Required new sensory, motor, and integrative controls for location and capture of larger preycontrols for location and capture of larger prey

Anterior end of nerve cord enlarged as a Anterior end of nerve cord enlarged as a tripartite brain tripartite brain Forebrain, midbrain, and hindbrainForebrain, midbrain, and hindbrain Brain was protected by cartilaginous or bony Brain was protected by cartilaginous or bony

cranium (skull)cranium (skull) Paired special sense organs for vision, Paired special sense organs for vision,

equilibrium, and sound evolved equilibrium, and sound evolved Other receptors that evolvedOther receptors that evolved

Mechanoreceptors, chemoreceptors, Mechanoreceptors, chemoreceptors, electroreceptors, and olfactory receptorselectroreceptors, and olfactory receptors



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Neural Crest and Ectodermal PlacodesNeural Crest and Ectodermal Placodes Development of vertebrate head and special sense organs Development of vertebrate head and special sense organs

lead to rise of these innovationslead to rise of these innovations Neural crestNeural crest

Derived from ectodermal cells in the embryonic neural tube Derived from ectodermal cells in the embryonic neural tube Contributes to formation of: cranium, pharyngeal skeleton, tooth Contributes to formation of: cranium, pharyngeal skeleton, tooth

dentine, some cranial nerves, ganglia, Schwann cells, and some dentine, some cranial nerves, ganglia, Schwann cells, and some endocrine glandsendocrine glands

May also regulate development tooth enamel and pharyngeal May also regulate development tooth enamel and pharyngeal musclesmuscles

Ectodermal placodesEctodermal placodes Plate-like ectodermal thickenings on either side of neural tubePlate-like ectodermal thickenings on either side of neural tube Give rise to olfactory epithelium, lens of eye, inner ear epithelium, Give rise to olfactory epithelium, lens of eye, inner ear epithelium,

some ganglia, some cranial nerves, lateral-line mechanoreceptors, some ganglia, some cranial nerves, lateral-line mechanoreceptors, and electroreceptorsand electroreceptors

Placodes also induce formation of taste budsPlacodes also induce formation of taste buds



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Evolutionary HistoryEvolutionary History

The Earliest VertebratesThe Earliest Vertebrates OstracodermsOstracoderms

Until recently, earliest known vertebrate fossils Until recently, earliest known vertebrate fossils were armored jawless fishes called were armored jawless fishes called ostracodermsostracoderms

Found in the late Cambrian deposits in United Found in the late Cambrian deposits in United States, Bolivia and AustraliaStates, Bolivia and Australia

Small, heavily armored, jawless, and lacked Small, heavily armored, jawless, and lacked paired finspaired fins


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Early Jawless Fish: Ostracoderms


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Evolutionary HistoryEvolutionary History

Vertebrates Vertebrates GnathostomesGnathostomes

All living and extinct jawed vertebrates All living and extinct jawed vertebrates

Agnathans,Agnathans, defined by the absence of jaws defined by the absence of jaws Living agnathans (jawless vertebrates), the Living agnathans (jawless vertebrates), the

lampreys and hagfisheslampreys and hagfishes


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Shark StructureEvidence that gill supports resemble jaw structure:

Evolutionists believe that the jaws arose from the cartilage gill supports


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Early Jawed Fish: Placoderm and Acanthodian


Agnatha Chondrichthyes Osteichthyes Amphibia Aves Mammalia

JAWSJaws helped vertebrates to become successful predators.

VERTEBRAEVertebrates have a segmented backbone.

FOUR LIMBSFour limbs let animals move from the water to life on land.

FEATHERSFeathers insulate birds from the cold and allow for flight.

HAIRHair helps mammals to maintain constant body temperatures by roviding insulation from the cold.

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23-1 CHAPTER 23 Chordates Chordates. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23-2 The Chordates: