20 September

Topic One--Characteristics of cnidarians

• nematocysts (stinging cells)
  
• alternation of generations
  
• polyp stage (non-sexual stage) buds medusae stage (sexual stage) , medusae produces either eggs or sperm (sexes are separate)
  
• sexual products fuse to produce zygote. zygote undergoes mitotic divisions to produce multicellular larval stage called a "planula larvae"

Zoologist by the name of Hadzi believes that cnidarians are ancestral to rest of the metazoans.

Topic Two--On becoming larger
1. stationery or attached (sessile)organisms, to miximize foodgetting, become cylindrical with circular oral surface. The same is true of free floating (pelagic) filter feeders (such as medusae)
2 to get larger you need support--Cnidaria do this via the production of a non-cellular mesoglea
3 can use gastrovascular cavity as skeleton.  hydrostatic skeleton
4 later after the shelly revolution, many metazoa use calcium carbonate for skeletal materials.

Topic Three-- a new level of construction-- triploblastic pseudocoelomates
Characteristics of nematode worms (Phylum Nematoda)

• complete digestive tract
• false body cavity (pseudocoel)
• third germ layer mesoderm
• outer layer of body is a cuticle (non-living fibers)