LIFESCI 1 Lecture Notes - Lecture 23: Viviparity, Chondrichthyes, Neural Crest
Document Summary
Sea stars, sea urchins, sea cucumbers, sand dollars. Defined by 3 main synapomorphies: radial symmetry in adults. Larvae are bilaterally symmetric a: adults have pentaradial symmetry (5-sided radial symmetry, an endoskeleton of calcium carbonate, a water vascular system. Predators distracted or is satisfied by digestive tract. Urchins in high densities can completely remove kelp forests-> sever the stipe above the holdfast. The echinoderm phyla is more closely related to vertebrates than to cnidarians. Dorsal hollow nerve cord runs parallel to a notochord. Muscle contractions on either side-> fishlike movement: myotomes-striated muscles. Both larvae and adults have pharyngeal gill slits-> feeding and gas exchange. Basket filters food particles that goes into the stomach and water exits the pharyngeal slits. Leading hypothesis for origin of jaw: natural selection acted on developmental regulatory genes that determine gill arch morphology. Jaws and gills arches have similar bone or cartilaginous morphology. Muscles that move both structures have the same embryonic origin.
