Phylum Chordata Urochordata, Cephalochordata, and Vertebrates

Characteristics 1.Bilateral symmetry, deuterostome 2.At some stage: notochord, pharyngeal slits or pouches, dorsal tubular nerve cord, postanal tail 3.Endostyle or thyroid gland 4. Complete digestive tract 5. Ventral contractile blood vessel (heart)

1. The notochord Supportive, dorsal cord, runs through body cavity to tailSupportive, dorsal cord, runs through body cavity to tail Prevent compression on anteroposterior axis (head to tail)Prevent compression on anteroposterior axis (head to tail) Allows for lateral (side to side) movementAllows for lateral (side to side) movement In adult vertebrates, cartilage or bone replace notochordIn adult vertebrates, cartilage or bone replace notochord

2. Pharyngeal slits Openings between digestive tract and outsideOpenings between digestive tract and outside –Some do not open out – pharyngeal pouches –Ancestrally used for feeding (some still do) –Gills for gas exchange –In terrestrial vertebrates, mainly embryonic

3. 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 –Sensory –Perception –Integration –Motor response

4. Postanal tail Extends posteriorly beyond anal openingExtends posteriorly beyond anal opening Notochord or vertebral column support tailNotochord or vertebral column support tail

Subphylum Urochordata Tunicates or sea squirtsTunicates or sea squirts Ascidians – largest classAscidians – largest class –Sessile adults –Solitary or colonial Appendicularians & thaliaceansAppendicularians & thaliaceans –Planktonic as adults Dominant life form in some areasDominant life form in some areas

Sessile tunicates Attach to solid substrateAttach to solid substrate Unattached end has 2 openingsUnattached end has 2 openings –Oral Opposite of attached endOpposite of attached end Takes water inTakes water in Serves as mouthServes as mouth –Atrial siphon Lets water outLets water out

Tunicate body wall Tunic – connective-tissue-like coveringTunic – connective-tissue-like covering –Appears as gel – often quite tough –Proteins, salts, and cellulose –Blood vessels, etc… may be incorporated –Root-like stolons may connect to substrate or colony

Tunicate Muscles Longitudinal and circular muscles change shapeLongitudinal and circular muscles change shape Work against elastic tunic and hydrostatic skeletonWork against elastic tunic and hydrostatic skeleton

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

Big old pharynx Tentacles around oral opening keep large objects out.Tentacles around oral opening keep large objects out. Pharyngeal slits called stigmas feature cilia that bring water into pharynx  stigma  atrium  out atrial siphonPharyngeal slits called stigmas feature cilia that bring water into pharynx  stigma  atrium  out atrial siphon

Digestion Continues from pharynx along mucus tract created by endostyleContinues from pharynx along mucus tract created by endostyle Digestion occurs in stomachDigestion occurs in stomach Absorption occurs in intestineAbsorption occurs in intestine Exits through anus (near atrial siphon)Exits through anus (near atrial siphon)

Gas exchange Occurs in pharynx as water circulatesOccurs in pharynx as water circulates

Circulation Heart near base of pharynxHeart near base of pharynx One vessel toward endostyle, one toward digestive organs and gonadsOne vessel toward endostyle, one toward digestive organs and gonads Direction of flow changes (?????)Direction of flow changes (?????)

Excretion Ammonia diffuses into waterAmmonia diffuses into water Amoeboid cells in blood sequester uric acid in intestineAmoeboid cells in blood sequester uric acid in intestine Pyloric glands may have excretory functionsPyloric glands may have excretory functions

Reproduction MonoeciousMonoecious Internal or external fertilizationInternal or external fertilization Cross fertilization is the ruleCross fertilization is the rule

Development Starts as free swimming larva, does not feedStarts as free swimming larva, does not feed Attaches to substrateAttaches to substrate –Outer epidermis shrinks –Brings notochord and tail inside –180° turn to make digestive tract U shaped

Subphylum Cephalochordata Lancelets – clearly demonstrate 4 chordate characteristicsLancelets – clearly demonstrate 4 chordate characteristics 2 genera2 genera –Branchiostoma (amphioxus) –Asymmetron 45 species45 species Worldwide and coastal in clean sand substratesWorldwide and coastal in clean sand substrates

Body Plan Small and tadpole-like (up to 5 cm long)Small and tadpole-like (up to 5 cm 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’d Notochord runs from tail to head (origin of name)Notochord runs from tail to head (origin of name) Most notochord cells are muscle cellsMost notochord cells are muscle cells –Contract – become more rigid –Relax – become more flexible

Swimming Muscles on side of notochord cause undulationsMuscles on side of notochord cause undulations Longitudinal ventrolateral folds stabilizeLongitudinal ventrolateral folds stabilize Dorsal and caudal (tail) fins aid in swimmingDorsal and caudal (tail) fins aid in swimming

From front to back Anterior oral hood protects cirri – fingerlike feeding tentaclesAnterior oral hood protects cirri – fingerlike feeding tentacles Posterior of oral hood has mouth leads to pharynx with many pharyngeal slits supported by gill barsPosterior of oral hood has mouth leads to pharynx with many pharyngeal slits supported by gill bars Atrium forms outside pharynxAtrium forms outside pharynx Atrium opening is called atrioporeAtrium opening is called atriopore

Eating Filter feeders, eat mostly buriedFilter feeders, eat mostly buried Large particles build up and are shaken off of cirriLarge particles build up and are shaken off of cirri Water carries small food particles in  stick to endostyle-created mucus  digestion is extracellular & intracellularWater carries small food particles in  stick to endostyle-created mucus  digestion is extracellular & intracellular

Eating cont’d Blind ending offshoot of the gut called a midgut cecum secretes digestive enzymesBlind ending offshoot of the gut called a midgut cecum secretes digestive enzymes Anus on left side of ventral finAnus on left side of ventral fin

Other maintenance No true heart, vessel contractions move blood which has amoeboid cellsNo true heart, vessel contractions move blood which has amoeboid cells Excretory tubules work with blood vessels in coelomExcretory tubules work with blood vessels in coelom Coelom is reduced and limited to small canalsCoelom is reduced and limited to small canals