First complex animals Intro to Animal Development 650 mya Soft-bodied; radial & bilateral symmetry Today’s topics: • The origin of multicellular animals • Variation in animal body plans • Intro to Development 29 March 2010 Simple Animal Phylogeny Is this your ancestor? Colonial Choanoflagellates Individual choanoflagellate are the sister group to all other animals Choanoflagellates OTHER EUKARYOTES Sponges Animals Collar cell (choanocyte) Other animals Not fully multicellular organisms Sponges Anatomy of a sponge Fig 33.4 1 It’s what’s between cells that defines Tissue Compatibility multicellularity in animals. Integrin http://www.scielo.br/scielo.php?pid=S1982-56762008000500007&script=sci_arttext Fig. 32-UN1 Fig. 32-7 Common ancestor of all animals Metazoa Sponges (basal animals) Ctenophora Eumetazoa Cnidaria (a) Radial symmetry Bilateria (mostanimals) True Acoela (basal tissues bilaterians) Deuterostomia Bilateral summetry Lophotrochozoa Three germ layers Ecdysozoa (b) Bilateral symmetry Fig. 32-9 Fig. 32-11 “Porifera” Protostome development Deuterostome development Silicea (examples: molluscs, (examples: echinoderm, Metazoa annelids) chordates) Calcarea (a) Cleavage ANCESTRAL Eight-cell stage Eight-cell stage COLONIAL Ctenophora FLAGELLATE Eumetazoa Cnidaria Acoela Deuterostomia Spiral and determinate Radial and indeterminate (b) Coelom formation Echinodermata Key Bilateria Coelom Ectoderm Chordata Mesoderm Archenteron Endoderm Platyhelminthes Coelom Lophotrochozoa Rotifera Mesoderm Blastopore Blastopore Mesoderm Ectoprocta Solid masses of mesoderm Folds of archenteron split and form coelom. form coelom. Brachiopoda (c) Fate of the blastopore Anus Mouth Mollusca Annelida Digestive tube Ecdysozoa Nematoda Mouth Anus Arthropoda Mouth develops from blastopore. Anus develops from blastopore. 2 Fig. 32-2 Developmental Processes Blastula and Gastrula Blastocoel Endoderm Cleavage Cleavage Blastula Ectoderm Archenteron Zygote Eight-cell stage Gastrulation Essential concepts Gastrula Blastocoel Blastopore • Cell Determination & Differentiation Cross section of blastula • Differential Rate & Timing of cell division • Programmed cell death • Tissue and Organ development Fig. 47-UN3 The cells in the three germ layers have defined fates in the adult: Gastrulation Sea urchin Frog Chicken Details differ, but all result in the development of 3 tissue layers Fig 47.14 3 .