Gastrulation and neurulation (frog)

Neurulation animation (human)

Phylum ChordataSubphylum Urochordata (Tunicata)Subphylum Cephalochordata“Craniata” groupSubphylum Vertebrata

Superclass Agnatha

Superclass GnathostomataClass PlacodermiClass ChondrichthyesClass AcanthodiiClass OsteichthyesClass AmphibiaClass ReptiliaClass MammaliaClass Aves

Urochordata

Sessile filter feeder – cilia move water and food, filtering in pharyngeal ‘pouch’ (pharynx)

Urochordata

Water + FoodIn

Getsfiltered

WaterOut

Endostyle – ciliated groove within pharynx

secretes mucous for food capture metabolizes iodine - homologous to

thyroid

Endostyle

Urochordata

Monoecious (hermaphroditic) - each individual produces male and female gametes. Gametes

released

Urochordata

Tunic – polysacchrides w/tunicin secreted by mantle

Adult lacks most chordate synapomorphies

Urochordata

Urochordata larvae

Eyespot (ocellus) andstatocyst

Non-tunicate Urochordates

Phylum ChordataSubphylum Urochordata (Tunicata)Subphylum Cephalochordata“Craniata” groupSubphylum Vertebrata

-Superclass Agnatha

Superclass GnathostomataClass PlacodermiClass ChondrichthyesClass AcanthodiiClass OsteichthyesClass AmphibiaClass ReptiliaClass MammaliaClass Aves

Motile filterfeeders

Ciliated wheel organ and pharynx Notochord – “hydroskeleton” Stiffness of notochord under neural

control

Cephalochordata

amphioxus

Notochord extendsinto anterior end

Amphioxus

Tail musculature and associated nerves & vessels are segmented.

‘Metamerism”

Cephalochordata

myomeres

Amphioxus

Circulatory system with dorsal and ventral aorta.

Cephalochordata

Metapleural fold – stability for swimming

Cephalochordata

In text, Euchordates = Somitichordates

What were early chordates like?

Pikaia gracilens - 530 million years ago

myomeres (muscle blocks) skeletal notochord cephalization

Cambrian explosion - ~550 million

y.a. Burgess shale

It’s a long way from amphioxusOh, a fish-like thing appeared among the annelids one day,It hadn't any parapods or setae to display.It hadn't any eyes or jaws or ventral nervous cord.But it had a lot of gill slits and it had a notochord.Chorus:It's a long way from amphioxus, it's a long way to us.It's a long way from amphioxus to the meanest human cuss.It's good-bye to fins and gill slits, and welcome lungs and hair.It's a long, long way from amphioxus, but we all came from there.It wan't much to look at and it scarce knew how to swim.And Nories was very sure it hadn't come from him.The Molluscs wouldn't own it and the Arthropods got sore.So the poor thing had to burrow in the sand along the shore.

"My notochord shall change into a chain of vertebrae,And, as fins, my metapleural folds will agitate the sea.""My tiny dorsal nervous cord shall be a mighty brain.And the vertebrates shall dominate the animal domain."

Kiss off, you dang annelids!

Phylum ChordataSubphylum Urochordata (Tunicata)Subphylum Cephalochordata“Craniata” groupSubphylum Vertebrata

-Superclass Agnatha

-Superclass GnathostomataClass PlacodermiClass ChondrichthyesClass AcanthodiiClass OsteichthyesClass AmphibiaClass ReptiliaClass MammaliaClass Aves

Chordates with skulls, neural crest cartilagenous, fibrous or bony encases brain & sense organs

Craniatacontains hagfish and all vertebrates

Hagfish

Lamprey

Sensory, digestive and respiratory anatomy

Craniata

Neural crest cellsNC cells are found in all craniates and give rise to a variety of structures

QuickTime™ and a Animation decompressor are needed to see this picture.

It’s nice to have a neural crest….

pigment cells gill arches, jaw ganglia in ANS base of skull induce skin ‘structures’

Selection for predatory characteristics

active feeders muscular gut tube for filtering

Craniata vs. ‘protochordates’

Pikaia gracilens Haikouella

Craniates were originally linked w/arthropods, annelids, mollusks

But essential differences in development

Chordate metamerism doesn’t involve coelom as in annelids

Evolutionary scenarios

Garstang (p.44) Euchordates (Somitochordates) evolved

via paedomorphosis (a type of heterochrony)

Paedomorphosis: Adult form of the descendant species retains juvenile features of ancestral species.

Linking the subphyla

Adult salamanderw/gills

Garstang: Mutation caused development of sexual maturity in a non-metamorphosing lineage of Urochordata – better locomotion

Early craniates – larger, more mobile than cephalochordata. Driven by predation?

Conodonts - 540-230 m.y. ago after Pikaia, the next fossil Chordates microfossils of teeth, probably in

pharynx

A new hard substance appears: mineralized tissue – calcium phosphate (hydroxyapatite)

Cool thing about conodonts