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Lecture 6 ANIMAL EVOLUTION: THE VERTEBRATES. Lancelets. Live in near-shore marine sediments Three to 7 cm long Have all the characteristics of chordates Use notochord and muscles for swimming motions just like tunicates. Have simple brain and head.
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Lancelets • Live in near-shore marine sediments • Three to 7 cm long • Have all the characteristics of chordates • Use notochord and muscles for swimming motions just like tunicates. • Have simple brain and head. • Have closed circulatory systemunlike tunicates. • Mode of respiration by diffusion of gases via thin skin.
Lancelets • Filter feeders: • cilia beats water into mouth cavity • food gets trap in mucus of pharynx • trapped food delivered to the rest of the gut. • Have large food-trapping area relative to the overall body length