Phylum Chordata

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PoriferaPorifera PlatyhelminthesPlatyhelminthes MolluscaMollusca ArthropodaArthropoda

HemichordataHemichordataCnidariaCnidaria NemerteaNemertea AnnelidaAnnelida

EchinodermataEchinodermataChordataChordataLophophoresLophophores

ProtozoansProtozoans

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Chordates

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Chordate Relatives• Common ancestry revealed by dorsal

nerve tube and pharyngeal gill slits

• Gill slits form (throat pocketings) at some time during development; used for feeding or gas exchange

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Deuterostomes

• the first opening (the blastopore) becomes the anus, while in protostomes it becomes the mouth.

Phylum Hemichordata• Three body regions

– Proboscis– Collar– Trunk

• Deuterostome• Gill slits• Open circulatory

system• Dorsal and ventral

nerve cord8

Phylum Chordata

• Three subphyla unified by having a notochord at some point in life cycle and metameric tail

• Notochord = densely packed muscle fibrils enclosed by sheath in rod shape; provides skeletal support– From which spinal column develops

• Metameric tail = repetition of similar segments; extends beyond anus

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Phylum Chordata

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Phylum Chordata

• Notochord• Gill slits or

pharyngeal pouches• Dorsal hollow nerve

cord• Postanal tail• Segmented muscles• Deuterostome

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Evolutionary Adaptations of Chordates

• From filter feeding ancestors to active predators

– Mobility

– Oxygen capture

– Digestion

– Circulation

– Nervous system16

Skeletal Changes

• Skeleton becomes stronger to work with bigger muscles

• Allows more rapid movement

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Oxygen Capture

• Gill slit and muscular pharynx will move more water over gills

– More oxygen is extracted from water

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Circulation

• Stronger heart to circulate blood faster

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Digestion

• Digest more food

– Muscularized gut

– Digestive glands

• Liver

• Pancreas

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Nervous System

• More complex for better– Motor control of

body to capture food– Sensory detection of

the animals environment

– Integration centers (brain)

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Brain With Three Parts

ForebrainMidbrainHindbrain

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Chordate SubphylaChordate Subphyla• Phylum.Phylum. ChordataChordata

– Subphylum.Subphylum. UrochordataUrochordata

– Subphylum.Subphylum. CephalochordataCephalochordata

– Subphylum.Subphylum. VertebrataVertebrata

• Phylum.Phylum. ChordataChordata

– Subphylum.Subphylum. UrochordataUrochordata

– Subphylum.Subphylum. CephalochordataCephalochordata

– Subphylum.Subphylum. VertebrataVertebrata

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Subphylum Urochordata• 3000 species of tunicates or sea squirts• Earliest derivative of chordate line• Adults bear no resemblance to other chordates, but

larval features indicate nerve cord and notochord• These disappear during metamorphosis• Only chordate feature remaining = gill slits (filter feed)

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Subphylum Urochordata

• Sea squirts

• Gill slits (pharyngeal slits)

• Notochord

– Only in larva

• Adult has tunic

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Sea Squirts

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Subphylum Urochordata• Soft-bodied marine filter feeders• Wide variety of sizes, shapes, and colonial structure• All have outer covering (tunic) containing tunicin

(cellulose-like) and in/ex-current siphons

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Subphylum Cephalochordata• Small group of 23 species of

lancelets or amphioxus

• Fish-like and free swimming, also burrow in sand with only head protruding

• Unique feeding apparatus for suspension feeding (buccal cirri/gill slits)

• Resemble vertebrates more; may represent living descendants of vertebrates 28

Subphylum Cephalochordata

• Amphioxus• Notochord length of

body• Dorsal hollow nerve

cord• Gill slits• Segmented muscles

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Amphioxus

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• Around 49,000 species of vertebrates• Significant not in size or age of group, but

its morphological diversity, structural complexity, and trophic dominance

• Three novelties bind all vertebrates

Subphylum Vertebrata

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Subphylum Vertebrata• Neural crest tissue = specialized kind of

ectoderm that gives rise to nervous system, retina, gill cartilage, and pigment cells

• Enlargement of anterior end of neural tube to form the brain

• Endoskeleton = backbone composed of vertebrae (bony/cartilaginous segments replace notochord during development), cranium (bony/cartilaginous housing for brain), paired pectoral and pelvic appendages

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Subphylum Vertebrata• All are bilaterally symmetrical with regional differentiation• Head region = houses sensory organs, brain, anterior

opening to digestive tract• Trunk region = body cavities that house viscera (internal

organs)• Tail or caudal region = lacks viscera, but has muscles and

skeleton (function in locomotion, reduced, or specialized)

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Subphylum Vertebrata• Metamerism (serial repetition of body parts) limited

to trunk muscles, skeleton (vertebrae and ribs), and the nerves associated with trunk

• All have gills at some point in life cycle (breathing organs or transient developmental structures)

• Closed circulatory system = arteries move blood to periphery from multi-chambered heart, veins move blood from periphery to heart, capillaries

• Myomeres associated with endoskeleton

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Vertebrate Classes

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Vertebrate Diversity

• Major evolutionary innovations among vertebrate groups fall into four categories:

1. Musculoskeletal system2. Nervous system3. Respiratory/circulation systems4. Nature of the egg

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Musculoskeletal system

• Most primitive in jawless vertebrates (hagfish, lampreys), have reduced braincase and cartilaginous gill-arch supports

• Hagfish = only notochord• Lamprey = notochord strengthened by

addition of small arches of cartilage in anterior trunk segments and small blocks of cartilage posteriorly--These are evolutionary precursors to vertebrae!

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Musculoskeletal system• All other vertebrates:

– replacement of notochord with bony* vertebrae--articulate, protective housing for nerve cord

– development of pectoral/pelvic appendages (from fins to limbs)

– appearance of jaws associated with braincase

*cartilage in sharks/rays-descended from bony ancestors

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Nervous System• Increased structural complexity allowed an

elaborate nervous system to evolve

• Cephalization: elaboration of the anterior end of spinal cord to form hollow brain and sensory organs (protected by skull)

• Peripheral nervous system: paired nerves in every body segment (relay brain’s messages to periphery)

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Nervous System• Autonomic nervous system: function

automatically without voluntary control by brain– Sympathetic: increases activity, slow

digestion– Parasympathetic: decreases activity,

stimulate digestion– This complementary system best

developed in mammals so they can maintain metabolic activity while still able to respond to external conditions

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Respiratory/Circulation• Respiration:

– Vertebrates require more oxygen than inverts, birds/mammals = highest demands (endothermic)

– Soft skin, moist environment (eel, amphibian) = gas exchange across skin in addition to respiratory organ

– Gills or lungs = derived from the pharynx

– Water pumped across gills, get gas exchange 41

Respiratory/Circulation

– Air breathed into lung, gas exchange across epithelial lining

– Birds also have air sacs extending from lungs into many parts of body

– Mammals have diaphragm to forcefully pull air in/expel air out

Respiratory/Circulation

• Circulation:– Allied with respiratory

system: transports oxygen, nutrients, and water to cells and removes wastes/carbon dioxide

– All systems closed: heart, arteries, veins, capillaries

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Respiratory/Circulation

– In gilled, 2-chamber heart: one atrium, one ventricle, blood enters heart via veins, leaves via aortic arches in gills (gas exchange), blood proceeds to rest of body

– In amphibians, aortic arches are reduced and modified into vessels in order to pass blood from lungs to 3-chambered heart (atrium separated by septum, one ventricle)

Respiratory/Circulation• Circulation:

– In snakes and lizards, ventricle also has septum (incomplete 4-chambers)

– In birds and mammals, complete separation of oxygenated/deoxygenated blood, 4-chambered heart, efficient system with no mixing gives greater blood volume and higher blood pressure (needed for metabolic requirements)

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Excretion

– Kidneys = separate food/water from excess salt/waste in blood

The Egg

• Eggs enclosed by plasma membrane internally and vitelline membrane externally

• Fish and amphibian eggs pass down oviduct where chitinous chorion or gelatinous protein-polysaccharide material added (anamniote egg = no amniotic membrane)

• External fertilization; moist climate to prevent desiccation

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The Egg

• Evolution of amniote egg: equipped with extra membrane layers of protection (amnion, yolk sac, chorion, allantois) as well as a leathery/calcareous shell

• In reptiles and mammals (monotremes); fertilization internal; subject to predation

• Marsupials and placental mammals retain young internally (helps young develop to an advanced stage before born)

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