• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata

– Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Urochordata • Sessile filter feeder – cilia move water and food,

filtering in pharyngeal ‘pouch’ (pharynx)

Water + Food

In

Gets

filtered

Water

Out

• 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

• Adult lacks most chordate synapomorphies

Urochordata

Urochordata larvae

Eyespot and

statocyst

• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata

– Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Cephalochordata • Motile filterfeeders

– ciliated wheel organ and pharynx

– Notochord – “hydroskeleton”

– Stiffness of notochord under neural control

amphioxus

Notochord extends

into anterior end

Cephalochordata

• Amphioxus

• Tail musculature and associated nerves & vessels are segmented.

– ‘Metamerism” myomeres

Cephalochordata

• Amphioxus

• Circulatory system with dorsal and ventral aorta.

• Metapleural fold – stability for swimming

Cephalochordata

In text, Euchordates = Somitichordates

• Pikaia gracilens - 530 million years ago

– myomeres (muscle blocks)

– skeletal notochord

– cephalization

• Cambrian explosion - ~550 million y.a.

– Burgess shale

• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata – Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

Craniata

• Chordates with skulls, neural crest

– cartilagenous, fibrous or bony

– encases brain & sense organs

contains hagfish and all vertebrates

Hagfish

Lamprey

Craniata • Sensory, digestive and respiratory anatomy

Neural crest cells • NC 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’

Craniata vs. ‘protochordates’

• Selection for predatory characteristics

– active feeders

– muscular gut tube for filtering

Evolutionary scenarios • Craniates were originally linked

w/arthropods, annelids, mollusks

– But essential differences in development

– Segmentation is different

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 salamander

w/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

Cool thing about conodonts

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

Hagfish • Scavenge dead, dying fish and invertebrates. Have

funnel-like mouths - tongue rasps off food.

Vertebrates • Metameric skeletal elements flanking the nerve

cord.

• Neural arch was first element to evolve

Hagfish

Lamprey

Shark

• Phylum Chordata

– Subphylum Urochordata (Tunicata)

– Subphylum Cephalochordata

– Subphylum Craniata

-Vertebrata • Superclass Agnatha

• Superclass Gnathostomata – Class Placodermi

– Class Chondrichthyes

– Class Acanthodii

– Class Osteichthyes

– Class Amphibia

– Class Reptilia

– Class Mammalia

– Class Aves

• “Ostracoderms” – 430-370 million years ago - early jawless fish

– head shields w/mineralized bone

– small bottom-dwelling

• Calcium phosphate mineralized tissue makes head shield and is related to teeth and scales

– enamel and dentine

– developmental interaction of epidermis and dermis

Ancestral jawless fish

• Usually no paired fins

• Notochord mostly remains

• Single nostril

• Main groups of modern jawless fish:

– Hagfish (Myxiniformes)

– Lamprey (Petromyzontiformes)

Similarities in these two groups are probably due

to evolutionary convergence (homoplasy)

Lamprey respiration

• Water flows in mouth, through respiratory tube and out gills

• Respiratory tube internally connects gill pores

• Specialized flap - velum can close off anterior end of respiratory tube

!!

• Branchial muscles squeeze water in and out of respiratory tube and over gills

• “Tidal ventilation”

!!

• Ammocetes - larval form of lamprey

– up to 7 years

• Uses muscular movements to make feeding current.