Invertebrate Chordates

Invertebrate Chordates - tunicate characteristics; thus, a...

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Invertebrate Chordates Not all chordates are vertebrates. Some chordates are invertebrates, lacking a vertebral column. In these invertebrate chordates, the notochord persists and is never replaced by the vertebral column. Subphylum Urochordata The subphylum Urochordata contains 1,250 species of tunuicates that have gill slits. Adults have a body composed of an outer tunic with an incurrent and excurrent siphon. When they are disturbed, tunicates tend to squirt water out. Water passes into a pharynx and out numerous gill slits, the only chordate characteristic that remains in adults. Microscopic particles adhere to a mucous secretion in the pharynx and are eaten. The larvae are bilaterally symmetrical and have the three chordate characteristics. Tunicate larva metamorphose into the sessile adult. Beating of numerous cilia lining the inside of the pharynx creates a current to move water through a tunicate. Some suggest larvae became sexually mature without developing
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Unformatted text preview: tunicate characteristics; thus, a urochordate larva was ancestral to vertebrates; or a cephalochordate larva may have been ancestral to vertebrates. Subphylum Cephalochordata The lancelets have three chordate characteristics. The 23 species of lancelets are in the genus Branchiostoma in the subphylum Cephalochordata. Their elongated, lance-shaped body resembles the lancelet, a two-edged surgical knife. They inhabit shallow coastal waters; they lie partly buried in sandy substrates and filter feed. Lancelets feed on microscopic particles filtered from the constant stream of water that enters the mouth and exits through the gill slits into an atrium that opens at the atriopore. Lancelets retain the three chordate characteristics as an adult. The notochord extends from head to tail, accounting for the name "Cephalochordata." Lancelets have segmented muscles and their dorsal hollow nerve cord has periodic branches....
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Invertebrate Chordates - tunicate characteristics; thus, a...

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