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Invertebrate chordates have features linking them to vertebrate
chordates.
Section 2: Invertebrate Chordates
K
What I Know
W
What I Want to Find Out
L
What I Learned
Essential Questions
• What are the features of invertebrate chordates that place them in the phylum
Chordata?
• What are the features of invertebrate chordates that place them with
invertebrates?
• What are the similarities between the adaptations of lancelets and sea
squirts?
Invertebrate ChordatesCopyright © McGraw-Hill Education
Review
• deuterostome
New
• chordate
• invertebrate chordate
• notochord
• postanal tail
• dorsal tubular nerve cord
• pharyngeal pouch
Invertebrate ChordatesCopyright © McGraw-Hill Education
Vocabulary
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
• Invertebrate chordates are deuterostomes with additional features that
echinoderms lack.
• Include the lancelet (amphioxus) and tunicates
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
• Chordates have four distinctive features at some point in their development:
• A dorsal tubular nerve cord
• A notochord
• Pharyngeal pouches
• A postanal tail
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
• Chordates also have a coelom and segmentation
• Invertebrate chordates have a dorsal tubular nerve cord, a notochord,
pharyngeal pouches, a postanal tail, and possibly an ancestral thyroid gland.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
Notochord
• The notochord is a flexible, rodlike structure that extends the length of the
body.
• Allows the body to bend rather than shorten during muscle contractions
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
Postanal tail
• A postanal tail is a structure used primarily for locomotion and is located
behind the digestive system and anus.
• Tails in nonchordates contain a portion of the digestive tract.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
Dorsal tubular nerve cord
• The dorsal tubular nerve cord is located dorsal to the digestive organs and is
a tube shape.
• The anterior end of this cord becomes the brain and the posterior end
becomes the spinal cord during development of most chordates.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
Pharyngeal pouches
• Pharyngeal pouches connect the muscular tube that links the mouth cavity
and the esophagus.
• Have slits for filter feeding and gills in aquatic chordates; in terrestrial
chordates, developed into the tonsils and the thymus gland.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate Chordate Features
Ancestral thyroid gland
• Thyroid gland regulates metabolism, growth, and development
• Invertebrate chordates have an endostyle, cells that secrete proteins similar
to a thyroid.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Diversity of Invertebrate Chordates
• All invertebrate chordates are marine animals.
• 23 species of lancelets
• 1250 species of tunicates
Invertebrate ChordatesCopyright © McGraw-Hill Education
Diversity of Invertebrate Chordates
Lancelets
• Small, fishlike animals without scales
• Burrow their bodies into the sand in shallow
seas
• Filter feeder
Invertebrate ChordatesCopyright © McGraw-Hill Education
Diversity of Invertebrate Chordates
Lancelets
• Swim with a fishlike motion
• No heads or sensory structures other than light receptors and small sensory
tentacles
• The nervous system consists of main branching nerves and a simple brain.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Diversity of Invertebrate Chordates
Tunicates
• Sessile
• Only in the larval stages do they show typical
chordate features
• The only chordate feature that remains in the
adult tunicate is pharyngeal gill slits and the
thyroid gland.
Tunicates
Animation
FPO
Add link to animation from page 805 here.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Invertebrate ChordatesCopyright © McGraw-Hill Education
Evolution of Echinoderms and Invertebrate Chordates
Phylogeny of echinoderms
• Fossil record of echinoderms extends back to the Cambrian period
• Ancient echinoderms may have been sessile and bilaterally symmetric.
Invertebrate ChordatesCopyright © McGraw-Hill Education
Evolution of Echinoderms and Invertebrate Chordates
Phylogeny of invertebrate chordates
• Development of the notochord allowed for significant advancement in motion
and body form.
• Many unanswered questions about invertebrate chordate evolution
Invertebrate ChordatesCopyright © McGraw-Hill Education
Review
Essential Questions
• What are the features of invertebrate chordates that place them in the phylum
Chordata?
• What are the features of invertebrate chordates that place them with
invertebrates?
• What are the similarities between the adaptations of lancelets and sea
squirts?
Vocabulary
• chordate
• invertebrate chordate
• notochord
• postanal tail
• dorsal tubular nerve cord
• pharyngeal pouch
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