01:119:116 Lecture Notes - Lecture 4: Hagfish, Actinistia, Agnatha
24 Mar 2018
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Shared derived characteristics **fig 32. 10 a. b. c. Other organisms do this - convergent evolution (one trait appeared more than 1 time separately) Ex: sea stars, sea urchins, sand dollars, sea cucumbers. Adults - often 5-part symmetry (technically still bilateral) Notochord - flexible support structure, runs down the back i. Trait only seen embryonically, lose as adults ii. iii. iv. Dorsal, hollow nerve chord - runs down dorsal side, filled with fluid. Pharyngeal slits or clefts - tissues on neck side/gills. Increased genetic complexity -> more complex body plan. Fused pelvic girdle- efficiently transmits forces through body (only in tetrapods!!) Amnion: membrane that forms fluid-filled sac around embryo. Know the order in which the derived traits appeared - which are most ancestral/most derived. Hair, fat layer under skin to retain heat. Platypus and echidnas - only australia and new guinea. Placenta: structure for nutrient exchange from mother to embryo. Also called :placental mammals" - have complex placenta.
