An Introduction to Animal Diversity  What Is an Animal?  An Overview of Animal Phylogeny and Diversity  The Origins of Animal Diversity

What Is an Animal?  Multicellular, eukaryotic, heterotrophic, ingestion feeder, stores glycogen, nervous system, no cell walls, muscle system, sexual, flagellated sperm, dominant diploid  Zygote  cleavage  blastula  gastrula  larva with metamorphosis

Figure 32.1 Early embryonic development (Layer 1)

Overview of Animal Diversity and Phylogeny  Diversified during Precambrian and Cambrian periods  Monophyletic  Parazoans-first branch, lack true tissues  Radiata and bilateria two major branches of Eumetazoa  Evolution of body cavities  Protostomes and deuterostomes

Parazoa  Sponges  “beside the animals”  Simple aquatic and marine forms

Eumetazoa Two major branches:  1. Radiata-radial symmetry, top and bottom, no front, back, or sides, diploblastic larva  2. Bilateria-bilateral symmetry, triploblastic, cephalization

Importance of Coelom  Acoelomates-no body cavity, Platyhelminthes  Pseudocoelomates-fluid filled body cavity, partially lined with mesoderm, Nematoda  Coelomates-fluid filled, completely lined with mesoderm, Annelida  Coelom-body cavity that protects internal organs

Protostomes and Deuterostomes Protostomes:  Mollusks, Annelids, Arthropods  Spiral cleavage  Determinate cleavage  Blastopore forms the mouth  schizocoelous Deuterostomes:  Echinoderms and Chordates  Radial cleavage  Indeterminate cleavage  Blastopore forms the anus  Enterocoelous

The Origins of Animal Diversity  Colonial protist origin during Cambrian Explosion  Evidence from fossil beds: Burgess Shale, Yunnan region, Greenland  Why such rapid diversification? 1. Adaptive radiation 2. Predator-prey relationships 3. Higher concentration of oxygen

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