23-1 CHAPTER 23 Chordates Chordates

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The Chordates: Characteristics The Chordates: Characteristics Structural Plan Name chordata comes from the notochord Name chordata comes from the notochord 5 Hallmark chordate characteristics 5 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)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics of Chordates Muscle segments Mouth Pharyngeal pouches Anus Tail Hollow nerve cord Notochord

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chordates share features with some invertebrates: Chordates share features with some invertebrates: Bilateral symmetry Bilateral symmetry Coelom Coelom Metamerism Metamerism Cephalization Cephalization Deuterostomes (like echinoderms) Deuterostomes (like echinoderms) The Chordates: Characteristics The Chordates: Characteristics

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Traditional and Cladistic Classification of the Chordates Traditional classification Traditional classification Protochordata (no skull) are separated from Vertebrata that have a skull Protochordata (no skull) are separated from Vertebrata that have a skull Vertebrates may be divided into Agnatha (jawless) and Gnathostomata (having jaws) Vertebrates may be divided into Agnatha (jawless) and Gnathostomata (having jaws) Gnathostomata is subdivided into Pisces with fins and Tetrapoda, usually with two pair of limbs Gnathostomata is subdivided into Pisces with fins and Tetrapoda, usually with two pair of limbs

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Five Chordate Hallmarks Notochord Always found at some embryonic stage Always found at some embryonic stage First part of the endoskeleton to appear in the embryo First part of the endoskeleton to appear in the embryo Serves as an axis for muscle attachment Serves as an axis for muscle attachment In protochordates (no skull) and jawless vertebrates, In protochordates (no skull) and jawless vertebrates, Persists throughout life Persists throughout life

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display In vertebrates In vertebrates Series of cartilaginous or bony vertebrae form notochord Series of cartilaginous or bony vertebrae form notochord In most vertebrates In most vertebrates Notochord displaced by vertebrae Notochord displaced by vertebrae Remnants may persist between or within vertebrae Remnants may persist between or within vertebrae Five Chordate Hallmarks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Dorsal Tubular Nerve Cord Anterior end enlarges to form the brain Anterior end enlarges to form the brain Cord is produced in embryo by infolding of ectodermal cells on the dorsal side of body Cord is produced in embryo by infolding of ectodermal cells on the dorsal side of body Five Chordate Hallmarks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Pharyngeal Pouches and Slits Pharyngeal slits lead from pharyngeal cavity to the outside Pharyngeal slits lead from pharyngeal cavity to the outside Form by the inpocketing of the ectoderm and the evagination of endoderm of pharynx Form by the inpocketing of the ectoderm and the evagination of endoderm of pharynx In aquatic chordates In aquatic chordates 2 pockets break through to form pharyngeal slit 2 pockets break through to form pharyngeal slit In amniotes In amniotes Pockets may not break through and only grooves are formed Pockets may not break through and only grooves are formed Five Chordate Hallmarks

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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display In tetrapods In tetrapods Pharyngeal pouches give rise to a variety of structures, including the Eustachian tube, middle ear cavity, tonsils and parathyroid glands Pharyngeal pouches give rise to a variety of structures, including the Eustachian tube, middle ear cavity, tonsils and parathyroid glands Perforated pharynx functions as filter- feeding apparatus in protochordates Perforated pharynx functions as filter- feeding apparatus in protochordates Fishes added a capillary network with thin gas-permeable walls Fishes added a capillary network with thin gas-permeable walls Led to evolution of gills Led to evolution of gills Five Chordate Hallmarks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Endostyle or Thyroid Gland Endostyle or its derivative, the thyroid gland, found in all chordates Endostyle or its derivative, the thyroid gland, found in all chordates Some cells in endostyle secrete hormones similar to the thyroid gland of adult lampreys and the remainder of vertebrates Some cells in endostyle secrete hormones similar to the thyroid gland of adult lampreys and the remainder of vertebrates Five Chordate Hallmarks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Postanal Tail Postanal tail, plus musculature, provided motility Postanal tail, plus musculature, provided motility Efficiency increased in fishes but became smaller or vestigial in later lineages Efficiency increased in fishes but became smaller or vestigial in later lineages Five Chordate Hallmarks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Subphylum Urochordata: Tunicata Diversity of Urochordata Approximately 3000 species of tunicates identified Approximately 3000 species of tunicates identified Occur in all seas and at all depth Occur in all seas and at all depth In most species, only the larval form bears all the chordate hallmarks In most species, only the larval form bears all the chordate hallmarks Adults lose many of these characters Adults lose many of these characters During adult metamorphosis During adult metamorphosis Notochord and tail disappear Notochord and tail disappear Dorsal nerve cord is reduced Dorsal nerve cord is reduced Urochordata include Urochordata include All Tunicates including Sea Squirts All Tunicates including Sea Squirts

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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tunic Heart Pharynx with gill slits Siphon to mouth Siphon from anus Anus Intestine Reproductive organs Stomach Adult Nonvertebrate Chordates Tunicate

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Subphylum Cephalochordata Diversity Lancelets Lancelets Slender, laterally flattened, translucent animals about 5–7 cm long Slender, laterally flattened, translucent animals about 5–7 cm long Live in sandy bottoms of coastal waters around the world Live in sandy bottoms of coastal waters around the world Also known as amphioxous Also known as amphioxous About 25 species of amphioxus are described About 25 species of amphioxus are described 5 occur in North American coastal waters 5 occur in North American coastal waters Many zoologists consider amphioxus a living descendant of ancestors that gave rise to both cephalochordates and vertebrates Many zoologists consider amphioxus a living descendant of ancestors that gave rise to both cephalochordates and vertebrates

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Amphioxus: Shows ALL 5 chordate characteristics Post-anal Tail

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Subphylum Vertebrate (Craniata) Adaptations That Guided Vertebrate Evolution Earliest vertebrates Earliest vertebrates Were substantially larger Were substantially larger Considerably more active Considerably more active Characterized by increased speed and mobility Characterized by increased speed and mobility Higher activity level and size of vertebrates Higher activity level and size of vertebrates Requires structures specialized in the location, capture, and digestion of food and adaptations designed to support a high metabolic rate Requires structures specialized in the location, capture, and digestion of food and adaptations designed to support a high metabolic rate

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Musculoskeletal Modifications Most vertebrates possess skeleton of cartilage or bone Most vertebrates possess skeleton of cartilage or bone Endoskeleton permits almost unlimited body size Endoskeleton permits almost unlimited body size Endoskeleton allows attachment of segmented muscles Endoskeleton allows attachment of segmented muscles Endoskeleton probably composed initially of cartilage and later gave way to bone Endoskeleton probably composed initially of cartilage and later gave way to bone Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Vertebral Column And Head skeleton Common in vertebrates Spinal cord

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Endoskeleton of living hagfishes, lampreys, sharks and their kin, and even some “bony” fishes, such as sturgeons, mostly composed of cartilage Endoskeleton of living hagfishes, lampreys, sharks and their kin, and even some “bony” fishes, such as sturgeons, mostly composed of cartilage Structural strength of bone is superior to cartilage Structural strength of bone is superior to cartilage Makes it ideal for muscle attachment in areas of high mechanical stress Makes it ideal for muscle attachment in areas of high mechanical stress Perhaps bone evolved, in part, as a means of mineral regulation Perhaps bone evolved, in part, as a means of mineral regulation Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Some of the most primitive fishes, including Ostracoderms and placoderms were partly covered in a bony, dermal armor Some of the most primitive fishes, including Ostracoderms and placoderms were partly covered in a bony, dermal armor Modified in later fishes as scales Modified in later fishes as scales Most vertebrates are protected with keratinized structures derived from the epidermis Most vertebrates are protected with keratinized structures derived from the epidermis Reptilian scales, hair, feathers, claws, and horns Reptilian scales, hair, feathers, claws, and horns Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Physiology Modifications of digestive, respiratory, circulatory, and excretory systems to meet increased metabolic demand Modifications of digestive, respiratory, circulatory, and excretory systems to meet increased metabolic demand To manage increased ingestion of food To manage increased ingestion of food Gut shifted from movement of food by ciliary action to muscular action Gut shifted from movement of food by ciliary action to muscular action Accessory digestive glands, the liver and pancreas, produced secretions that aided digestion Accessory digestive glands, the liver and pancreas, produced secretions that aided digestion Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Transport of nutrients gases, and other substances was enhanced by Transport of nutrients gases, and other substances was enhanced by Ventral 3-chambered heart Ventral 3-chambered heart Sinus venosus Sinus venosus Atrium Atrium Ventricle Ventricle Included hemoglobin Included hemoglobin Vertebrates possess paired kidneys to remove metabolic waste products and regulated body fluid composition Vertebrates possess paired kidneys to remove metabolic waste products and regulated body fluid composition Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display New Head, Brain, and Sensory Systems Shift from filter feeding to active predation Shift from filter feeding to active predation Required new sensory, motor, and integrative controls for location and capture of larger prey Required new sensory, motor, and integrative controls for location and capture of larger prey Anterior end of nerve cord enlarged as a tripartite brain Anterior end of nerve cord enlarged as a tripartite brain Forebrain, midbrain, and hindbrain Forebrain, midbrain, and hindbrain Brain was protected by cartilaginous or bony cranium (skull) Brain was protected by cartilaginous or bony cranium (skull) Paired special sense organs for vision, equilibrium, and sound evolved Paired special sense organs for vision, equilibrium, and sound evolved Other receptors that evolved Other receptors that evolved Mechanoreceptors, chemoreceptors, electroreceptors, and olfactory receptors Mechanoreceptors, chemoreceptors, electroreceptors, and olfactory receptors Subphylum Vertebrate (Craniata)

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Neural Crest and Ectodermal Placodes Development of vertebrate head and special sense organs lead to rise of these innovations Development of vertebrate head and special sense organs lead to rise of these innovations Neural crest Neural 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 dentine, some cranial nerves, ganglia, Schwann cells, and some endocrine glands Contributes to formation of: cranium, pharyngeal skeleton, tooth dentine, some cranial nerves, ganglia, Schwann cells, and some endocrine glands May also regulate development tooth enamel and pharyngeal muscles May also regulate development tooth enamel and pharyngeal muscles Ectodermal placodes Ectodermal placodes Plate-like ectodermal thickenings on either side of neural tube Plate-like ectodermal thickenings on either side of neural tube Give rise to olfactory epithelium, lens of eye, inner ear epithelium, some ganglia, some cranial nerves, lateral-line mechanoreceptors, and electroreceptors Give rise to olfactory epithelium, lens of eye, inner ear epithelium, some ganglia, some cranial nerves, lateral-line mechanoreceptors, and electroreceptors Placodes also induce formation of taste buds Placodes also induce formation of taste buds Subphylum Vertebrate (Craniata)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Evolutionary History The Earliest Vertebrates Ostracoderms Ostracoderms Until recently, earliest known vertebrate fossils were armored jawless fishes called ostracoderms Until recently, earliest known vertebrate fossils were armored jawless fishes called ostracoderms Found in the late Cambrian deposits in United States, Bolivia and Australia Found in the late Cambrian deposits in United States, Bolivia and Australia Small, heavily armored, jawless, and lacked paired fins Small, heavily armored, jawless, and lacked paired fins

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Evolutionary History Vertebrates Gnathostomes Gnathostomes All living and extinct jawed vertebrates All living and extinct jawed vertebrates Agnathans, defined by the absence of jaws Agnathans, defined by the absence of jaws Living agnathans (jawless vertebrates), the lampreys and hagfishes Living agnathans (jawless vertebrates), the lampreys and hagfishes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Shark Structure Evidence that gill supports resemble jaw structure: Evolutionists believe that the jaws arose from the cartilage gill supports

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. AgnathaChondrichthyesOsteichthyesAmphibia Aves Mammalia JAWS Jaws helped vertebrates to become successful predators. VERTEBRAE Vertebrates have a segmented backbone. FOUR LIMBS Four limbs let animals move from the water to life on land. FEATHERS Feathers insulate birds from the cold and allow for flight. HAIR Hair helps mammals to maintain constant body temperatures by roviding insulation from the cold. lamprey cartilaginous fish bony fish amphibians birds mammals