origin of chordates biol 495 – chapter two. comparative vertebrate anatomy
TRANSCRIPT
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Origin of Chordates BIOL 495 – Chapter Two
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Comparative
Vertebrate
Anatomy
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Abundance of Phyla #1 – Arthropoda #2 – Nematoda
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#3 – Mollusca #4 – Chordata
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Relative abundance of species in phyla
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Protostomes vs Deuterostomes Protostome Deutersotome
Cleavage
Coelom origin
Blastopore fate
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Chordate Features
1. Notochord*2. Pharyngeal Slits3. Endostyle or
Thyroid Gland*4. Dorsal Hollow
Nerve Cord*5. Postanal Tail*
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Notochord
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Pharyngeal Slits
Pharynx – part of digestive track immediately posterior to mouth
NOT really ‘gill slits’
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Endostyle or Thyroid Gland Endostyle – part of the filter feeding apparatus
Thyroid gland – hormone producing endocrine gland
Evidence for Homology:• Arise embryological from the same tissue (floor of the pharynx)• Are involve with iodine metabolism • Endostyle Thyroid Gland in Lampreys
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Dorsal Hollow Nerve Chord
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Postanal Tail
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“Protochordates”
‘grouped’ mainly by primitive features
pelagic larvabenthic adults (many sessile)
MyomeresSegmented blocks of muscle – outer body wall
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Hemichordata – Acorn Worms
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Hemichordata – Relationships?
Hemichordata Larva Echinoderm Larva
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Cephalochordata – Amphioxus
No anterior swelling of dorsal nerve cordMidgut cecum’s evolutionary fate?
Liver or pancreas perhaps
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Blood is colorless plasmaSame general circulation pattern as vertebrates: blood flows anteriorly into the ventral aorta, up to the dorsal aorta, posteriorly in the dorsal aorta. No ebb and flow pattern, even though they lack a heart
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Urochordata – Tunicates/Sea Squirts
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Has identifiable heart and rudimentary ‘brain’
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Chordate Origins?
Pikaia ~ 530 million years old
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Chordate Origins, Echinoderma grade ancestor?
Pedomorphosis
Hemichordata Larva Echinoderm Larva
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Another wrinkle: Inverted body plan
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