BIOL108 Lecture Notes - Lecture 15: Hydrostatic Skeleton, Bilateria, Opisthokont

• School: University of Alberta
• Department: Biology (Biological Sciences)
• Course: BIOL108
• Professor: Heather Proctor

Document Summary

Animals without true tissues include sponges and placozoans. Animals with true tisses = eumetazoa: 2nd split is based on symmetry radially: top and bottom but no left and right; diploblastic (endo & ecto) Bilateral: top, bottom, left and right (ex. lobster); triploblastic (endo=gut, ecto=skin. ^ these cushion internal organs from blows to outside body and allows internal organs to shift without deforming outside of body: fluid filled cavity can be used as hydrostatic skeleton, 3rd split involves embryo development of bilateria. Second invagination becomes mouth and first becomes anus or closes up (deutero=second) Radial cleavage; cleavage is indeterminate meaning cell could split and we can get two embryos later on explaining why humans can have identical twins. Mesoderm at one end of gut pinches off to make fluid filled hollows called enterocoely (entero=gut) Spiral cleavage; cleavage is determinate meaning each cell is destined to form some part of the later embryo and if some cells are removed = missing organs.