Animal Characteristics Multicellular Heterotrophs Monophyletic 5 key innovations in animal evolution 1 Symmetry 2 Tissues 3 Body Cavity 4 Various embryonic development patterns 5 Segmentation Gametic Life Cycle Haploid Sex Cells egg and sperm Diploid All other cells in the organism Haploid sperm and haploid egg fuse to form diploid zygote develops into diploid adult Zygote undergoes divisions and forms a blastula ball of cells Blastula divides into three germ layers Embryonic Development Embryonic Development Cells divide into three germ layers Ectoderm outer layer forms skin and nervous system Mesoderm middle layer forms skeleton and muscles Endoderm inner layer forms digestive system Body Cavity Coelom body cavity inside the organism that is isolated from the exterior of the animal houses internal organs Acoelomate Organism does not have a coelom Pseudocoelomate Organism has a coelom but it is between the mesoderm and endoderm tissue Coelomate Organism has a coelom and it is entirely within mesoderm tissue Invertebrates Organisms do not have a backbone Very diverse contain about 95 of all known animal species
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