NEXT EXAM: WEDNESDAY APRIL 20th No Class on Monday, April 18th Review Session This Friday, April 15th

Chapter 25 Key Points: Animals are the descendants of protists Animal phylogeny is not certain Major body plan transitions Tissues Symmetry Body cavity Dueterostome Segmentation Animals are morphologically and ecologically diverse but use many of the same genes

Traditional: - Emphasis on coelom - “Cumulative” relationship Molecular: - Emphasis on mode of growth - Chordates equally related to all protostomes Major group relations are the same - protostome relations change

25_2 Molecular phylogeny suggests that key body transitions can occur repeatedly Changes to tree are in protostomes Body cavities appear to have evolved several times Suggest that mode of growth is a conserved characteristic

Animals are morphologically diverse but use many of the same genes to pattern their bodies Genes that regulate the expression of other genes (transcription factors) are highly conserved between animals Code body parts and regions that develop into morphologically diverse structures p.495

Sponges -No symmetry -No tissue or organs -Direct descendent of choanoflagellate protists -Do have some specialized cells -Cells do recognize each other Fig 24_4

Sponge Bodies Fig 25_5 -Outside surface is epidermis -Inside surface lined with choanocyte cells -Flagella beat, move water through pores -Cells filter feed on small organisms in water -Different cell types

“Jelly Fish” - Radiata Two groups - Cnidaria and Ctenophora Have radial symmetry Have tissues Have outer (epidermis) and inner (gastrodermis) layers that form from 2 embryonic layers

Cnidarians are named for their “Cnidocytes” -Species can be medusa, polyp, or both Fig 25_8 -Cnidocytes are cell that contain “harpoon” like structures involved in prey capture -Unique to this phylum Fig 25_7