• Phylum Chordata
– Subphylum Urochordata (Tunicata)
– Subphylum Cephalochordata
– Subphylum Craniata
-Vertebrata
• Superclass Agnatha
Urochordata
• Sessile filter feeder – cilia move water and food,
filtering in pharyngeal ‘pouch’ (pharynx)
Water + Food
In
Water
Out
• Superclass Gnathostomata
–
–
–
–
–
–
–
–
Class Placodermi
Class Chondrichthyes
Class Acanthodii
Class Osteichthyes
Class Amphibia
Class Reptilia
Class Mammalia
Class Aves
Urochordata
• Endostyle – ciliated groove within pharynx
– secretes mucous for food capture
– metabolizes iodine - homologous to thyroid
Gets
filtered
Urochordata
• Monoecious (hermaphroditic) - each
individual produces male and female
gametes.
Gametes
released
Endostyle
Urochordata
Urochordata larvae
• Adult lacks most chordate synapomorphies
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
Cephalochordata
• Motile filterfeeders
– ciliated wheel organ and pharynx
– Notochord – “hydroskeleton”
– Stiffness of notochord under neural control
• Amphioxus
amphioxus
• Tail musculature and associated nerves &
vessels are segmented.
– ‘Metamerism”
myomeres
Notochord extends
into anterior end
Cephalochordata
• Amphioxus
• Circulatory system with dorsal and ventral
aorta.
Cephalochordata
• Metapleural fold – stability for swimming
• Pikaia gracilens - 530 million years ago
– myomeres (muscle blocks)
– skeletal notochord
– cephalization
In text, Euchordates = Somitichordates
• 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
contains hagfish and all vertebrates
Craniata
• Sensory, digestive and respiratory anatomy
• Chordates with skulls, neural crest
– cartilagenous, fibrous or bony
– encases brain & sense organs
Hagfish
Lamprey
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
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
• Garstang: Mutation caused development of
sexual maturity in a non-metamorphosing
lineage of Urochordata – better locomotion
• Conodonts - 540-230 m.y. ago
• Early craniates – larger, more mobile than
cephalochordata. Driven by predation?
Cool thing about conodonts
• A new hard substance appears: mineralized
tissue – calcium phosphate (hydroxyapatite)
– after Pikaia, the next fossil Chordates
– microfossils of teeth, probably in pharynx
Hagfish
• Scavenge dead, dying fish and invertebrates. Have
funnel-like mouths - tongue rasps off food.
Vertebrates
• Metameric skeletal elements flanking the nerve
cord.
Hagfish
Lamprey
• Neural arch was first element to evolve
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
• Ammocetes - larval form of lamprey
– up to 7 years
• Uses muscular movements to make feeding
current.
• “Tidal ventilation”
!!