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Unformatted text preview: 2/20/2008 1 Animal Diversity Invertebrates & Vertebrates Animalia Plantae Symbiosis of chloroplast ancestor with ancestor of green plants Symbiosis of mitochondrial ancestor 3 4 The Tree of Life mitochondrial ancestor with eukaryotes Possible fusion of bacteria and archaea yielded eukaryotes Common ancestor of all organisms 1 2 Leicontre & Le Guyader, 2006 Tree of Life Deuterostomia Radiata Protostomia Bilateria Metazoa Eumetazoa Ancestral colonial flagel ate Phylogeny based on morphological and developmental data Possible origin of metazoans from a colonial flagellated protist What is an animal? How did metazoans originate? 1 Early colony of protists; aggregate of identical cells 2 Hollow sphere (shown in cross section) 3 Beginning of cell specialization (cross section) 4 Infolding (cross section) 5 Gastrula-like protoanimal (cross section) Digestive cavity Reproductive cells Somatic cells Multi-cellular aggregations are common in nature: Example 1 Choanoflagellates colonial Choanozoan, sister taxa of all metazoans 2/20/2008 2 Monosiga brevicollis choanoflagellate, closest known relative of metazoans. Genome = 9200 genes King et al. Nature 451: 2008 Multi-cellular aggregations are common in nature: Example 2 Volox colonial freshwater chlorobionta-ulvophyta. The hollow colony is composed of biflagellated cells (above). The cells are connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will release small daughter colonies . Cleavage Cleavage Blastocoel Evo-Devo evidence metazoans: embryonic development in animals Zygote Eight-cell stage Blastula Cross section of blastula Blastocoel Endoderm Ectoderm Gastrula Blastopore Gastrulation Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Radial and indeterminate Cleavage Coelom Archenteron Eight-cell stage Spiral and determinate...
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