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Section 2: Invertebrate Chordates Invertebrate chordates have features linking them to vertebrate chordates. 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? Copyright © McGraw-Hill Education Invertebrate Chordates Vocabulary Review New • • • • • • • deuterostome Copyright © McGraw-Hill Education chordate invertebrate chordate notochord postanal tail dorsal tubular nerve cord pharyngeal pouch Invertebrate Chordates Invertebrate Chordate Features • Invertebrate chordates are deuterostomes with additional features that echinoderms lack. • Include the lancelet (amphioxus) and tunicates Copyright © McGraw-Hill Education Invertebrate Chordates 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 Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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 Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates Diversity of Invertebrate Chordates • All invertebrate chordates are marine animals. • 23 species of lancelets • 1250 species of tunicates Copyright © McGraw-Hill Education Invertebrate Chordates Diversity of Invertebrate Chordates Lancelets • Small, fishlike animals without scales • Burrow their bodies into the sand in shallow seas • Filter feeder Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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. Copyright © McGraw-Hill Education Invertebrate Chordates 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 Copyright © McGraw-Hill Education Invertebrate Chordates
