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