1. Gastrulation and neurulation (frog)
Neurulation animation (human)

2. Phylum Chordata Subphylum Urochordata (Tunicata)
Subphylum Cephalochordata
“Craniata” group
Subphylum Vertebrata
Superclass Agnatha
Superclass Gnathostomata
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Class Mammalia
Class Aves

4. Urochordata

5. Urochordata
Sessile filter feeder – cilia move water and food, filtering in pharyngeal ‘pouch’ (pharynx)
Water + Food In
Water
Out
Gets
filtered

6. Urochordata Endostyle – ciliated groove within pharynx
secretes mucous for food capture
metabolizes iodine - homologous to thyroid
Endostyle

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

8. Tunic – polysacchrides w/tunicin secreted by mantle

9. Urochordata
Adult lacks most chordate synapomorphies

10. Urochordata larvae
Eyespot (ocellus)
and
statocyst

12. Non-tunicate Urochordates

13. Phylum Chordata -Superclass Agnatha Subphylum Urochordata (Tunicata)
Subphylum Cephalochordata
“Craniata” group
Subphylum Vertebrata
-Superclass Agnatha
Superclass Gnathostomata
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Class Mammalia
Class Aves

14. Cephalochordata Motile filterfeeders Ciliated wheel organ and pharynx
Notochord – “hydroskeleton”
Stiffness of notochord under neural control
amphioxus
Notochord extends
into anterior end

15. Cephalochordata Amphioxus
Tail musculature and associated nerves & vessels are segmented.
‘Metamerism”
myomeres

16. Cephalochordata Amphioxus
Circulatory system with dorsal and ventral aorta.

17. Cephalochordata
Metapleural fold – stability for swimming

18. In text, Euchordates = Somitichordates

20. What were early chordates like?

21. Pikaia gracilens - 530 million years ago
myomeres (muscle blocks)
skeletal notochord
cephalization

23. Cambrian explosion - ~550 million y.a.
Burgess shale

25. It’s a long way from amphioxus
Kiss off, you dang annelids!
It’s a long way from amphioxus
Oh, 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."

26. Phylum Chordata -Superclass Agnatha Subphylum Urochordata (Tunicata)
Subphylum Cephalochordata
“Craniata” group
Subphylum Vertebrata
-Superclass Agnatha
-Superclass Gnathostomata
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Class Mammalia
Class Aves

27. Craniata Chordates with skulls, neural crest
contains hagfish and all vertebrates
Chordates with skulls, neural crest
cartilagenous, fibrous or bony
encases brain & sense organs
Hagfish
Lamprey

28. Craniata
Sensory, digestive and respiratory anatomy

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

30. It’s nice to have a neural crest….
pigment cells
gill arches, jaw
ganglia in ANS
base of skull
induce skin ‘structures’

31. Craniata vs. ‘protochordates’
Selection for predatory characteristics
active feeders
muscular gut tube for filtering
Pikaia gracilens Haikouella

32. Evolutionary scenarios
Craniates were originally linked w/arthropods, annelids, mollusks
But essential differences in development
Chordate metamerism doesn’t involve coelom as in annelids

33. Linking the subphyla 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.
Adult salamander
w/gills

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

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

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

37. Cool thing about conodonts
A new hard substance appears: mineralized tissue – calcium phosphate (hydroxyapatite)