Phylum ChordataPhylum ChordataUrochordata, Urochordata,

Cephalochordata, and Cephalochordata, and VertebratesVertebrates

CharacteristicsCharacteristics1.1. Bilateral symmetry, Bilateral symmetry,

deuterostomedeuterostome2.2. At some stage: At some stage:

notochord, notochord, pharyngeal slits or pharyngeal slits or pouches, dorsal pouches, dorsal tubular nerve cord, tubular nerve cord, postanal tailpostanal tail

3.3. Endostyle or Endostyle or thyroid glandthyroid gland

4. Complete 4. Complete digestive tractdigestive tract

5. Ventral contractile 5. Ventral contractile blood vessel blood vessel (heart)(heart)

1. The notochord1. The notochord• Supportive, dorsal cord, runs Supportive, dorsal cord, runs

through body cavity to tailthrough body cavity to tail• Prevent compression on Prevent compression on

anteroposterior axis (head to tail)anteroposterior axis (head to tail)• Allows for lateral (side to side) Allows for lateral (side to side)

movementmovement• In adult vertebrates, cartilage or In adult vertebrates, cartilage or

bone replace notochordbone replace notochord

2. Pharyngeal slits2. Pharyngeal slits• Openings between digestive tract Openings between digestive tract

and outsideand outside– Some do not open out – pharyngeal Some do not open out – pharyngeal

pouchespouches– Ancestrally used for feeding (some still Ancestrally used for feeding (some still

do)do)– Gills for gas exchangeGills for gas exchange– In terrestrial vertebrates, mainly In terrestrial vertebrates, mainly

embryonicembryonic

3. Tubular Nerve Cord3. Tubular Nerve Cord• Responsible for success!Responsible for success!• Runs dorsal to notochordRuns dorsal to notochord• Expand anteriorly as brainExpand anteriorly as brain• Responsible for complex systemsResponsible for complex systems

– SensorySensory– PerceptionPerception– IntegrationIntegration– Motor responseMotor response

4. Postanal tail4. Postanal tail• Extends posteriorly beyond anal Extends posteriorly beyond anal

openingopening• Notochord or vertebral column Notochord or vertebral column

support tailsupport tail

Subphylum UrochordataSubphylum Urochordata• Tunicates or sea squirtsTunicates or sea squirts• Ascidians – largest classAscidians – largest class

– Sessile adultsSessile adults– Solitary or colonialSolitary or colonial

• Appendicularians & thaliaceansAppendicularians & thaliaceans– Planktonic as adultsPlanktonic as adults

• Dominant life form in some Dominant life form in some areasareas

Sessile tunicatesSessile tunicates• Attach to solid substrateAttach to solid substrate• Unattached end has 2 openingsUnattached end has 2 openings

– OralOral• Opposite of attached endOpposite of attached end• Takes water inTakes water in• Serves as mouth Serves as mouth

– Atrial siphonAtrial siphon• Lets water outLets water out

Tunicate body wallTunicate body wall• Tunic – connective-tissue-like Tunic – connective-tissue-like

coveringcovering– Appears as gel – often quite toughAppears as gel – often quite tough– Proteins, salts, and celluloseProteins, salts, and cellulose– Blood vessels, etc… may be Blood vessels, etc… may be

incorporatedincorporated– Root-like stolons may connect to Root-like stolons may connect to

substrate or colonysubstrate or colony

Tunicate MusclesTunicate Muscles• Longitudinal and circular muscles Longitudinal and circular muscles

change shapechange shape• Work against elastic tunic and Work against elastic tunic and

hydrostatic skeletonhydrostatic skeleton

Tunicate Nervous systemTunicate Nervous system• Mostly in body wall (plexus) Mostly in body wall (plexus) • Single ganglion between openingsSingle ganglion between openings• Mechano- and chemoreceptors all Mechano- and chemoreceptors all

over body wall (more near openings)over body wall (more near openings)

Big old pharynxBig old pharynx• Tentacles around oral opening keep Tentacles around oral opening keep

large objects out.large objects out.• Pharyngeal slits called stigmas Pharyngeal slits called stigmas

feature cilia that bring water into feature cilia that bring water into pharynx pharynx stigma stigma atrium atrium out out atrial siphonatrial siphon

DigestionDigestion• Continues from pharynx along Continues from pharynx along

mucus tract created by endostylemucus tract created by endostyle• Digestion occurs in stomachDigestion occurs in stomach• Absorption occurs in intestineAbsorption occurs in intestine• Exits through anus (near atrial Exits through anus (near atrial

siphon)siphon)

Gas exchangeGas exchange• Occurs in pharynx as water Occurs in pharynx as water

circulatescirculates

CirculationCirculation• Heart near base of pharynxHeart near base of pharynx• One vessel toward endostyle, one One vessel toward endostyle, one

toward digestive organs and gonadstoward digestive organs and gonads• Direction of flow changes (?????)Direction of flow changes (?????)

ExcretionExcretion• Ammonia diffuses into waterAmmonia diffuses into water• Amoeboid cells in blood sequester Amoeboid cells in blood sequester

uric acid in intestineuric acid in intestine• Pyloric glands may have excretory Pyloric glands may have excretory

functionsfunctions

ReproductionReproduction• MonoeciousMonoecious• Internal or external fertilizationInternal or external fertilization• Cross fertilization is the ruleCross fertilization is the rule

DevelopmentDevelopment• Starts as free swimming larva, does Starts as free swimming larva, does

not feednot feed• Attaches to substrateAttaches to substrate

– Outer epidermis shrinksOuter epidermis shrinks– Brings notochord and tail insideBrings notochord and tail inside– 180° turn to make digestive tract U 180° turn to make digestive tract U

shapedshaped

Subphylum Subphylum CephalochordataCephalochordata

• Lancelets – clearly demonstrate 4 Lancelets – clearly demonstrate 4 chordate characteristicschordate characteristics

• 2 genera 2 genera – BranchiostomaBranchiostoma (amphioxus) (amphioxus)– AsymmetronAsymmetron

• 45 species45 species• Worldwide and coastal in clean sand Worldwide and coastal in clean sand

substratessubstrates

Body PlanBody Plan• Small and tadpole-like (up to 5 cm Small and tadpole-like (up to 5 cm

long)long)• Laterally flattenedLaterally flattened• Weak swimmers, live in burrowsWeak swimmers, live in burrows• Filter feeders, anterior end exposedFilter feeders, anterior end exposed

Body plan cont’dBody plan cont’d• Notochord runs from tail to head Notochord runs from tail to head

(origin of name)(origin of name)• Most notochord cells are muscle cellsMost notochord cells are muscle cells

– Contract – become more rigid Contract – become more rigid – Relax – become more flexibleRelax – become more flexible

SwimmingSwimming• Muscles on side of notochord cause Muscles on side of notochord cause

undulationsundulations• Longitudinal ventrolateral folds Longitudinal ventrolateral folds

stabilizestabilize• Dorsal and caudal (tail) fins aid in Dorsal and caudal (tail) fins aid in

swimmingswimming

From front to backFrom front to back• Anterior oral hood protects cirri – Anterior oral hood protects cirri –

fingerlike feeding tentaclesfingerlike feeding tentacles• Posterior Posterior ofof oral hood has mouth oral hood has mouth

leads to pharynx with many leads to pharynx with many pharyngeal slits supported by gill pharyngeal slits supported by gill barsbars

• Atrium forms outside pharynxAtrium forms outside pharynx• Atrium opening is called atrioporeAtrium opening is called atriopore

EatingEating• Filter feeders, eat mostly buriedFilter feeders, eat mostly buried• Large particles build up and are Large particles build up and are

shaken off of cirrishaken off of cirri• Water carries small food particles in Water carries small food particles in

stick to endostyle-created mucus stick to endostyle-created mucus digestion is extracellular & digestion is extracellular & intracellularintracellular

Eating cont’dEating cont’d• Blind ending offshoot of the gut Blind ending offshoot of the gut

called a midgut cecum secretes called a midgut cecum secretes digestive enzymesdigestive enzymes

• Anus on left side of ventral finAnus on left side of ventral fin

Other maintenanceOther maintenance• No true heart, vessel contractions No true heart, vessel contractions

move blood which has amoeboid move blood which has amoeboid cellscells

• Excretory tubules work with blood Excretory tubules work with blood vessels in coelomvessels in coelom

• Coelom is reduced and limited to Coelom is reduced and limited to small canalssmall canals