LIFESCI 2 Lecture Notes - Lecture 24: Water Vascular System, Tube Feet, Symmetry In Biology
Document Summary
Week 8 (11/22: deuterostomes: mouth develops second, anus develops first, radial cell divisions, phylum echinodermata--spiny-skins (sea stars, sea urchins, sea cucumbers, sand dollars, monophyletic group, 3 synapomorphies: Adults have pentaradial symmetry (5-sided radial symmetry) Dorsal hollow nerve chord parallel to notochord. Muscle contractions on either side --> fishlike movement: urochordates tunicates (sea squirts) Both larvae & adults have pharyngeal gill slits: feeding & gas exchange. Leading hypothesis for origin: natural selection acted on developmental regulatory genes that determine gill arch morphology. 1. ) jaws & gill arches have similar bony or cartilaginous morphology. 2. ) muscles that move both structures have same embryonic origin. 3. ) both structures are derived from neural crest cells. 4. ) regulatory gene expression patterns are similar in both structures: vertebrates hagfish & lampreys. Brains protected by cranium but lack jaw. Hagfish lack any sort of vertebral column. Lampreys have cartilage along the dorsal hollow nerve cord: chondrichthyes cartilaginous fish (sharks, skates, rays, reproduction = internal fertilization.
