BIOL 150 Lecture Notes - Lecture 12: Ctenophora, Protostome, Lophotrochozoa
Document Summary
Sponges lack many tissue types of other animals. Cnidaria - jellyfish, corals, sea pens, hydra, anenomes. Ectoderm - gives rise to skin and nervous system. Endoderm - gives rise to lining of digestive tract. Mesoderm - dives rise to circulatory system, muscle, and internal structures such as bone and most organs. Enables movement through water, air, or through a substrate. Radially symmetric organisms equally likely to encounter prey in any direction. Bilaterally symmetric organisms encounter prey at one end. Evolution of head or anteriro region, brain (cerebrial ganglion) Cnidarians, ctnenophores, and very few triploblasts lace a coelom (acoelmoates) Almost all ceolomated are bilaterally symmetric; 99% animal species. Pilot 185 rrna study several surprising finginds and implications (1997) Rejected hypothesis that annelids and arthropods are closely related based on shared segmentation of body parts. Demonstrated two model organisms, the nematode and the fruit fly are much more closely related than previoulsy thought. Bilateria underwent a major split between protostomes and deuterostomes.
