Time Line of Animal Evolution n 1 st

Time Line of Animal Evolution n 1 st Fossil evidence of animals 570 mya = Proterozoic Era n Adaptive radiation in early Cambrian Period of the Paleozoic Era n Cambrian Explosion due to n increased oxygen in atmosphere n more energy n predators become more mobile

Evolution of Animals n Some type of Protist mutated to become multicellular n Multicellular organisms start as a single cell (zygote) and grow into organisms with groups of specialized cells performing different functions n All animals are multicellular

Proterospongia = Protist & common ancestor to all animals?

Proterospongia: Colonial, Unicellular Protists

Sponge collar cells

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

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

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

All other Animals have True Tissues

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

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

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

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