Echinoderms and Invertebrate Chordates Ch 29 Echinodermata Endoskeleton

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/Ss 24 TLqb. Cf. U http: //youtu. be/A 100 m 5 Epf. FI – Water enters and leaves through madreporite, a sievelike, disk-shaped opening on the upper surface of body • Bilaterally symmetrical, ciliated larvae • Deuterostomes (mouth forms 2 nd)

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=s 95 rf. Gncl. X 0 • 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)