Chordates

Chordates

Characteristics that Unify thisGroup:

1.Notochord

2.Hollow, dorsal nerve cord

3.Pharyngeal slits

Chordate Characteristics

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Notochords

•Long, flexible supportrod

•Dorsal, just belownerve cord

•Usually replaced bybackbone in earlydevelopment

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Hollow, Dorsal Nerve Cord

•Just below thenotochord

•Front end developsinto the brain

•Many nerves branch torest of body from thismain cord

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Comparison of Arthropods andVertebrates

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Pharyngeal Slits

•In aquatic chordates,these develop into gillslits

•Only chordates havepharyngeal gill slits

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Pharyngeal Slits

•In terrestrial chordatesthe pharyngeal slitsclose up at an earlystage in development

•In humans, the embryodoesn’t ever developactual slits, but doesdevelop pharyngeal“pouches”

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Invertebrate Chordates –Tunicates and Lancelets

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Invertebrate Chordates –Tunicates

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Tunicates – Larvae and Adult

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Tunicates - larva

•Tadpole-shapedlarvae are freeswimming.

•Only the larvaehave thenotochord anddorsal nerve cord

•They Filterplankton andbreathe throughtheir pharyngealgill slits

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Tunicates - adults

•Adults developthroughmetamorphosis oflarval stage

•Are sessile, filter feedand breathe throughthe gill slits

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Lancelets

•Fish-like shape

•Half (at least) oftheir body isburied in the sand

•Filter-feeders

•Have mouth andup to 100pharyngeal slitsalong body

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Lancelets

•Havemuscle/nervearrangementsimilar to thatfound in ALLvertebrates

•No jaw

•Noappendages

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