Download Lecture 29 - Matthew Bolek

Introduction to Chordates
• Chapter 15
Basics
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Bilateral symmetry
Segmented body
Three germ layers
Well-developed Coelom
Endoskeleton
Complete digestive system
Closed circulatory system
Chordate Characters
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Notochord
Pharyngeal pouches
Postanal tail
Nerve cord (dorsal)
Notochord
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Flexible rod-like structure
First part of endoskeleton (in embryo)
Axis for muscle attachment
In most verts, its replaced by vertebrae
Pharyngeal pouches
• Pharyngeal slits: vary in degree and
function
– Aquatic chordates: leads to outside of cavity
– Amniotes: forms only groves
– Fish: became gills
Postanal tail
• Tail and musculature provide motility
– Fish: highly evolved
– Other groups: become vestigial
Nerve cord
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Dorsal to alimentary canal
Tubular
Brain on anterior end
Formed from ectoderm
SP: Urochordata
Tunicates
SP: Urochordata
Tunicates
• Found at all ocean depths
– Largely sessile
• Larval forms have all chordate features
– Adults loose many of these
• Notochord and tail disappear
• Dorsal nerve cord is reduced
• Tunic (test): protective covering around
animal
Adult Tunicates
Adult and Tadpole Larva of
Urochordate
SP: Urochordata
Example
• Ascidians: sea squirts
– More common intertidal animals
– Can be found attached to rocks
– Colonial and solitary forms
• Feeding
– Filter feed with mucus net
SP: Cephalochordata
Lancelets
• Marine
• Found in sediments near costal waters
• Feeding
– Filter feed with mucus net
Lancelet
Amphioxus
SP: Cephalochordata
Bauplan
• Long slender, translucent
• Has four chordate characters
• Is though to be living descendant of
ancestor that gave rise to vertebrates
SP: Vertebrata
• AKA Craniata: all groups have a
cranium
– braincase
• Thought to be monopyletic
• Share other important characteristics
SP: Vertebrata
• Fossil invertebrate chordates are rare
and known primarily from two fossil
beds.
• Pikaia from Cambrian Burgess Shale
Haidouella 530 MYO China
Haidouella 530 MYO China
The Early Vertebrates
• Ostracoderms- Armed Jawless Fishes 505
MYO
SP: Vertebrata
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Living Endoskeleton
Efficient Respiration (Pharynx)
Advanced Nervous System
Paired limbs
Living Endoskeleton
• Grows with body
– No molting
– Efficient use of materials
• Muscle attachment
• Protect body and body protects it
• Made from
– Bone
– Cartilage
Efficient Respiration (Pharynx)
• Pharynx is result of shift from filter
feeding
• Increased metabolic rate
– Addition of capillaries
– Muscular aortic arches
Advanced Nervous System
• Predation favored more complex nervous
system
– Eyes with lenses
– Paired eyes
• Two innovative adaptations
– Neural crest-forms cranium
– Specialized Sense Organs- nose, eyes, ears….
Paired limbs
• Pectoral and pelvic appendages
– Swimming stabilizers
• Jointed limbs
– Work well in terrestrial environments
The Big Picture
• Four major evolutionary events binds the
chordates into a group
– Many of these allowed chordates to be successful on
land
• Urochordates as adults appear to be sponges or
cnidarins, but as larvae they have all structures
shared by chordate
• Remember what it means to be a vertebrate…