Evolution of Animals Some type of Protist mutated to become multicellular instead of colonial Colonial cells live together but each cell can replicate autonomously Multicellular organisms start as a single cell (zygote) and grow into organisms with groups of specialized cells performing different functions All animals are multicellular

Proterospongia = Protist & common ancestor to all animals?

Time Line of Animal Evolution 1st Fossil evidence of animals 570 mya = Proterozoic Era as glaciers began to thaw Diversification (adaptive radiation) in early Cambrian Period of the Paleozoic Era Cambrian Explosion due to increased oxygen in atmosphere due to predators becoming mobile due to evolution of Hox genes = increased developmental flexability

Proterospongia: Colonial, Unicellular Protists

Sponge choanocytes (collar cells)

Phylum Porifera Sponges 3 types of cells No tissues Collar cells (choanocytes) Amoebocytes Epidermis cells (protective outer layer of cells) No tissues Cells held together by mesohyle (jelly) Skeleton of spicules & spongin protein

Intracelluar digestion Collar cells take in food by endocytosis Food digested in food vacuoles Some food passed to amoebocytes Amoebocytes carry food around sponge body. (circulaton)

Other Porifera Traits Asymmetrical = no symmetry Respiration by diffusion Excretion by diffusion Reproduction = male gametes released into water, filtered out of water by another sponge. Female gametes stay in mesohyle until fertilized. Zygote grows into a swimming larva. Larva settles to ground & becomes sessile adult

Eumetazoa = Animals with True Tissues

Phylum Cnidaria Have stinging cells = cnidocytes Have tentacles Have myocytes = muscle like cells that contract 1st predatory animals Have Radial symmetry = sit and wait predator 1st nervous system = nerve net & eye spots

Digestion & Circulation Have gastrovascular cavity for digestion & circulation 1st extra cellular digestion – cells lining GVC secrete digestive enzymes into GVC to digest food Evolutionary advantage = can eat larger food Cillia lining GVC push digested food particles around the body GVC branches into all tentacles: comes near all cells

Respiration & Excretion Respiration by diffusion Excretion by diffusion Both are possible since entire body is only a few cell layers away from external water

Reproduction = complex life cycle Medusa = swimming Polyp = sessile Medusa =sexual Egg & sperm External fertilizaion Polyp = asexual budding