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Section 26-2 Section 26-3 Animal Characteristics Heterotrophs must ingest others for nutrients Multicellular complex bodies No cell walls allows active movement Sexual reproduction no alternation of generations no haploid gametophyte Animal Evolution Cnidaria Porifera sponges jellyfish Nematoda Platyhelminthes Annelida Mollusca flatworms roundworms mollusks segmented worms Echinodermata Arthropoda insects spiders Jointed appendages redundancy, segmentation mobility specialization, mobility starfish Chordata vertebrates body & brain notochord size, mobility body size endoskeleton coelom digestive sys radial body cavity bilateral symmetry tissues distinct body plan; cephalization specialized structure & function, muscle & nerve tissue multicellularity specialization & body complexity Ancestral Protist body complexity digestive & repro sys bilateral Body Cavity Space for organ system development acoelomate ectoderm mesoderm endoderm increase digestive & reproductive systems increase food capacity & digestion increase gamete production Coelem mesoderm & endoderm interact during development allows complex structures to develop in digestive system ex. stomach pseudocoelomate ectoderm mesoderm endoderm pseudocoel coelomate ectoderm mesoderm coelom cavity endoderm protostome vs. deuterostome Early Embryonic Development Protostomes Gastrula Embryo Opening that forms first key Deuterostomes Protostomes Gastrula ( Embryo ( weeks) weeks) First opening Key to tissue layers Deuterostomes