Which of these organisms are animals? Figure 32.1 Which of these organisms are animals?

Animal Early Embryonic Development Cleavage Blastocoel Endoderm Blastula Ectoderm Archenteron Zygote Eight-cell stage Gastrulation Gastrula Figure 32.2 Early embryonic development in animals Blastocoel Blastopore Cross section of blastula

Three lines of evidence that choanoflagellates protists are closely related to animals Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES Sponges Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals Animals Collar cell (choanocyte) Other animals

(a) Mawsonites spriggi (b) Spriggina floundersi Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago 0.4 cm 1.5 cm Figure 32.4 Ediacaran fossils (a) Mawsonites spriggi (b) Spriggina floundersi

A Cambrian seascape Figure 32.5 A Cambrian seascape

Animal Body Symmetry (a) Radial symmetry (b) Bilateral symmetry Figure 32.7 Body symmetry (b) Bilateral symmetry

Triploblastic Animals Body Cavities Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) (a) Coelomate - true body cavity Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate Figure 32.8 Body cavities of triploblastic animals Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate - lack a body cavity

Protostome Deuterostome Development molluscs, annelids Deuterostome Development echinoderm, chordates (a) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate Key Coelom Ectoderm (b) Coelom formation Mesoderm Archenteron Endoderm Coelom Mesoderm Blastopore Blastopore Mesoderm Folds of archenteron form coelom. Solid masses of mesoderm split and form coelom. Figure 32.9 A comparison of protostome and deuterostome development Anus Mouth (c) Fate of the blastopore Digestive tube Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

“Porifera” Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Figure 32.10 A view of animal phylogeny based mainly on morphological and developmental comparisons Rotifera Protostomia A view of animal phylogeny based mainly on morphological and developmental comparisons Mollusca Annelida Arthropoda Nematoda

A view of animal phylogeny based mainly on molecular data Silicea “Porifera” Calcarea ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Cnidaria Eumetazoa Acoela Echinodermata Deuterostomia Chordata Bilateria Platyhelminthes Rotifera Ectoprocta Figure 32.11 A view of animal phylogeny based mainly on molecular data Lophotrochozoa Brachiopoda A view of animal phylogeny based mainly on molecular data Mollusca Annelida Nematoda Ecdysozoa Arthropoda

Ecdysis - Shedding of Exoskeleton Figure 32.12 Ecdysis

Lophotrochozoans Characteristics Lophophore Apical tuft of cilia Mouth Figure 32.13 Morphological characteristics found among lophotrochozoans 100 µm Anus (a) An ectoproct (b) Structure of a trochophore larva

Common ancestor of all animals Sponges (basal animals) Ctenophora Animal Phylogeny Common ancestor of all animals Sponges (basal animals) Metazoa Ctenophora Eumetazoa Cnidaria True tissues Acoela (basal bilaterians) Deuterostomia Bilateria (most animals) Bilateral summetry Lophotrochozoa Three germ layers Ecdysozoa

You should now be able to: List the characteristics that combine to define animals. Summarize key events of the Paleozoic, Mesozoic, and Cenozoic eras. Distinguish between the following pairs or sets of terms: radial and bilateral symmetry; diploblastic and triploblastic; spiral and radial cleavage; determinate and indeterminate cleavage; acoelomate, pseudocoelomate, and coelomate Compare the developmental differences between protostomes and deuterostomes.