Lecture #14

Phylum Chordata: The vertebrate Phylum

Phylum Chordata

• only 45,000 species• characteristics:– 1. bilaterally symmetrical– 2. notochord– 3. pharyngeal gill slits– 4. dorsal, hollow nerve cord– 5. post-anal tail– 6. complete digestive system– 7. thyroid gland– 8. ventral, contractile heart

Numbers 1 – 5 may be ina unique combination andare found at some stage in development

• Chordate classification characteristics:

• Notochord? No Echinoderms• Notochord? Yes keep evolving• Brain? No Urochordate

(tunicate)• Brain? Yes keep evolving• Head/Cranial cavity? No

Cephalochordate (lancelet)• Cranial cavity? Yes keep

evolving• Vertebral column? No Hagfish• Vertebral column? Yes

Lampreys & keep evolving baby!!!

Chordates

E ch i

n ode

r mat

a(s

iste

r gr o

up t o

ch o

rda t

e s)

Craniates

Vertebral column

Head

Brain

Notochord

Ancestral deuterostome

C ep h

a lo c

h ord

ata

(l an c

elet

s)M

y xi n

i(h

a gfi s

hes )

C ep h

a la s

p id o

mor

p hi

(l am

prey

s )

Uro

c ho r

data

(tu n

i ca t

e s)

Phylum Chordata

• notochord:– supportive rod that extends most of the animal’s

length – extends into the tail – dorsal to the body cavity– flexible to allow for bending but resists

compression– composed of large, fluid-filled cells encased in a

fairly stiff fibrous tissue– will become the vertebral column in many

chordates

Phylum Chordata

• dorsal, hollow nerve cord:– runs along the length of the body – dorsal to the

notochord– expands anteriorly as the brain– develops from ectoderm– BUT: in most vertebrates – nerve cord is solid and

is ventral to the vertebral column

Phylum Chordata

• pharyngeal gill slits:– series of openings in the pharyngeal region of the

embryo– develop as a series of pouches separated by

grooves– in some embryos – grooves develop into slits– used in primitive chordates for filter feeding– in aquatic vertebrates – transformed these

slits/pouches into gills– embryonic in terrestrial chordates

Phylum Chordata

• SubPhyla:– Urochodata: sea squirts (tunicates)• notochord, pharyngeal gill slits, and tail present in free-

swimming larvae

– Cephalochordata: amphioxus• all four chordate traits persist through life

– Hyperotreti: hagfishes• jawless, no paired appendages

– Vertebrata: vertebrates

Subphylum Cephalochordata

• known as the lancelets• earliest diverging group of chordates• get their name (Lancelet) from their blade-like shape• embryos develop: a notochord, a dorsal, hollow nerve

cord, pharyngeal gill slits and a post-anal tail• filter-feeders – cilia draw water into the mouth• swim like fishes – chevron shaped muscles on either side

of the notochord

Pharyngealslits or clefts

Mouth

Brain

Dorsal,hollow

nerve cordNotochordMusclesegments

Muscular,post-anal tail

Anus

Subphylum Urochordata

• tunicates• embryonic/larval stage has the

characteristics of the chordate• larva swims to a new substrate

and undergoes metamorphosis – to form the adult tunicate

• retain the pharyngeal gill slits in the adults

• water flows in through an incurrent siphon - filtered by a net of mucus on the pharyngeal gill slits

Incurrentsiphonto mouth

Excurrentsiphon

Pharynxwith

numerousslits

Atrium

Tunic

Excurrentsiphon

AnusIntestine

EsophagusStomach

Craniates• chordates with a head• head – consists of a brain, surrounded by a

skull, and other sensory organs• living craniates all share a series of unique

characteristics• most basic craniate – hagfish

https://www.youtube.com/watch?v=t5PGZRxhAyU

Vertebrates

• branching off from the primitive chordates involved innovations in the nervous system and skeleton– vertebraes have a more extensive skull– development of the vertebral column composed of vertebrae

• most vertebrates – vertebrae enclose a spinal cord (replaces the notochord)

– development of fin rays in aquatic vertebrates– development of limbs in terrestrial vertebrates

• adaptations in respiration and circulation– more efficient gas exchange system – gills are modified in aquatic

vertebrates; lungs in the terrestrial vertebrates– more efficient heart – 2 to 4 chambered

• adaptations in thermal regulation– warm blooded vs. cold blooded

• adaptations in reproduction– amniotic egg– placental animals

Vertebrate Taxonomy

• most basal vertebrate – lamprey– jawless

• development of jaws marked the evolution of the gnathostomes

• development of ray-finned fishes• development of lobed fins marked

the evolution of lobe-finned fishes• development of limbs marked the

development of amphibians and reptiles

• development of mammary glands marked the development of mammals

lungs marked the evolution

• Vertebrate classification requirements:

• Vertebral column? No Hagfish

• Jaws? No Lampreys• Bony skeleton? No Sharks,

Rays• Lobed fins? No? Ray finned

fish• Lung derivatives? No

Coelocanth• Legs? No Lungfish• Amniotic egg? No Amphibian• Milk? No Reptile• What’s left??? MAMMALS!!

ChordatesE c

h in o

der m

ata

(sis

ter g

r oup

t o c

h ord

a te s

)

CraniatesVertebrates

GnathostomesOsteichthyans

Lobe-finsTetrapods

Amniotes

Milk

Legs

Amniotic egg

Mineralized skeleton

Jaws

Vertebral column

Head

Brain

Notochord

Ancestral deuterostome

C ep h

a lo c

h ord

ata

(l an c

elet

s)M

y xi n

i(h

a gfi s

hes )

C ep h

a la s

p id o

mor

p hi

(l am

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s )C h

o nd r

ich t

h yes

(sh a

r ks ,

rays

, ch i

ma e

ras)

Acti

n opt

ery g

i i(r

a y- fi

n ned

fis h

e s)

Acti

n is ti

a(c

o el a

c ant

h us )

Dip

n oi

(l un g

fi sh e

s)

Uro

c ho r

data

(tu n

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e s)

Am

p hi b

i a(f

rog s

, sa l

a ma n

der s

)R e

p tili a

(tu r

t les,

sn a

kes ,

c ro c

o dile

s , b

ir ds)

Ma m

ma l

ia(m

amm

a ls )

Lobed fins

Lung derivatives