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Echinoderms and Invertebrate Chordates

Echinoderms and Invertebrate Chordates. Ch 29. Echinodermata. Endoskeleton, radial symmetry, simple nervous system, varied nutrition, water vascular system

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Echinoderms and Invertebrate Chordates

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  1. Echinoderms and Invertebrate Chordates Ch 29

  2. Echinodermata • Endoskeleton, radial symmetry, simple nervous system, varied nutrition, water vascular system • Water vascular system—hydraulic system that operates under water pressure, enables animal to move, exchange gases, capture food, excrete wastes • Move along surfaces and pry open food with tube feet http://youtu.be/Ss24TLqbCfUhttp://youtu.be/A100m5EpfFI • Water enters and leaves through madreporite, a sievelike, disk-shaped opening on the upper surface of body • Bilaterally symmetrical, ciliated larvae • Deuterostomes (mouth forms 2nd)

  3. Diversity of Echinoderms • ~6000 species exist today, 6 classes • Asteroidea: sea stars (25% of phylum) • most species have 5 rays, but some can have more than 40! • Ophiuroidea: brittle stars • Extremely fragile, rays can break off (helps survive predator attacks), propel themselves by slithering, tube feet for feeding • Echinoidea: sea urchins and sand dollars • Globe-/disk-shaped, covered with spines, no rays, tube feet for eating and modified as gills for respiration • Holothuroidea: sea cucumbers • Vegetable-like appearance, moves along ocean floor, expels tangled sticky mass of tubes through anus or ruptures and loses organs, which regenerate in a few weeks (evasion of predators) • Crinoidea: sea lilies and feather stars • Resemble plants, sea lilies only sessile echinoderms, feather stars sessile in larval form; use feathery arms to swim around • Concentricycloidea: sea daisies • Two species discovered in New Zealand, tube feet around edge of disk

  4. Invertebrate Chordates • All chordates have a notochord—a long, semirigid, rodlike structure between digestive system and dorsal hollow nerve cord • Made up of large, fluid-filled cells held within stiff fibrous tissue • Invertebrates: may retain notochord to adulthood • Vertebrates: notochord replaced with backbone • All chordates have dorsal hollow nerve cord • Develops from a plate of ectoderm that rolls into a hollow tube • Composed of cells surrounding fluid-filled canal above the notochord

  5. Embryonic invagination of the notochord and neural tube Anterior region with early central nervous system

  6. Commonalities in Chordates • All chordates have a notochord • All chordates have pharyngeal pouches • Paired openings in pharynx behind mouth • All chordates have a postanal tail • At some point in development • Development controlled by homeotic genes

  7. Diversity of Invertebrate Chordates • Tunicates (sea squirts): chordate features visible in larval stages http://www.youtube.com/watch?v=s95rfGnclX0 • Lancelets (similar to fish): spend most of their time buried in sand with only heads out to filter food from water

  8. Origins • Fossil record is limited because of soft bodies • Possibly arose from sessile animals that fed by tentacles (larval stages may be similar)

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