Echinoderms and Invertebrate Chordates
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Transcript of Echinoderms and Invertebrate Chordates
Echinoderms and Invertebrate Chordates
Ch 29
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/Ss24TLqbCfU http://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)
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
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
Embryonic invagination of the notochord and neural tube
Anterior region with early central nervous
system
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
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
Origins
• Fossil record is limited because of soft bodies• Possibly arose from sessile animals that fed by
tentacles (larval stages may be similar)