longitudinal rod of fluid-filled cells in the embyonic midline
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How does the notochord allow chordates to move?
It is not compressible but can bend. Producing undulations what muscle segments contract.
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Why are the muscles arranged in bilaterally?
Allows alternating left-right muscle contractions and produces waves of contractions going anterior to posterior.
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How do chordates increase the force they exert on their environment?
They increase their surface area, via a post anal tail and medial fins. More water can be pushed aside, more thrust is generated.
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What does the dorsal nerve cord develop from?
A plate of dorsal ectoderm (the most exterior of the 3 germ layers)
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What does the dorsal nerve cord develop in to?
the CNS! the brain anteriorly and the spinal cord posteriorly
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What do pharyngeal slits develop from?
pouches in the endoderm of the pharynx
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Describe the function of the pharyngeal slits
allow water to leave the body without passing through the digestive system, act as a suspension feeding device, make gas exchange efficient
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Describe the characteristics of the class cephalochordata
Lancelets: swim freely and feed on plankton, poorly developed head, notochord reaches up to anterior tip (not halfway like in vertebrates)
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Describe the characteristics of the class urochordata
Turnicates, jawless fish: once settled on a substrate undergoes radial metamorphis
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What do we think the ancestral chordate may have looked like and why do we think this?
Like a lanclet! They display key chordate characteristics and their lineage branches from the base of the chordate phylogenetic tree
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What are the derived characteristics of craniata?
formation of a head, neural crest, placodes
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What enabled craniates to develop more complex morphologies?
Duplication of Hox genes (craniates posses 2 or more sets of Hox genes, lanclets and turnicates only have one)
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What characteristics come with the development of a head - as in craniates
skull, tripartite brain, eyes and other sensory organs, muscular pharynx -development of respiratory gills
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What is the neural crest?
a collection of cells that appear near the dorsal margins of the closing neural tube in an embryo, they disperse throughout the body where they give rise to a number of structures
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What are placodes?
local thickenings of the ectoderm of the head and neck, give rise to neurones and sensory epithelia involved in smelling, tasting, hearing and balance
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Other cards in this set
Card 2
Front
What is the notochord?
Back
longitudinal rod of fluid-filled cells in the embyonic midline
Card 3
Front
How does the notochord allow chordates to move?
Back
Card 4
Front
Why are the muscles arranged in bilaterally?
Back
Card 5
Front
How do chordates increase the force they exert on their environment?
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