Introduction to Animal Evolution Ch. 32 AP Biology Ms. Haut

What is an Animal? Multicellular, heterotrophic eukaryotes Animal cells lack cell walls 2 tissues unique to animals: nervous and muscular Most reproduce sexually, with diploid stage dominating life cycle

Animal Development Zygote undergoes cleavage to form blastula During gastrulation embryonic tissues that develop into adult body parts form

Phylogenetic Tree of Animals

Parazoans Includes Phylum Porifera (sponges) Classified as parazoa because they lack true tissues

Eumetazoans Include nearly all other animal phyla Organisms that contain true tissues Radiata and bilateria are the major branches

Radiata Radial Symmetry Organisms that are sessile (attached to substratum) or plankton (drifting) Equips them to meet the environment equally from all sides –Cniderians (jellyfishes, corals, anenomes) –Ctenophora (comb jellies)

Bilateria Bilateral Symmetry Cephalization seen—concentration of sensory equipment (central nervous system) Equips them for mobile lifestyle 2 branches: –Organisms without body cavities (Acoelomates) –Organisms with body cavities (Pseudocoelomates and Coelomates)

Acoelomates Phylum Platyhelminthes (flatworms) Triploblastic (3 germ layers) animals with solid bodies (no cavity between digestive tract and outer body walls

Pseudocoelomates Phylum Rotifera (rotifers) Phylum Nematoda (roundworms) Triploblastic (3 germ layers) animals body cavity between digestive tract and outer body walls incompletely lined with mesoderm

Coelomates Body cavity completely lined by mesoderm 2 evolutionary lines –Protostomes –Deuterostomes

Protostomes Mollusks Annelids (segmented worms) Arthropods

Deuterostomes Echinoderms Chordata

Coelomates Distinguished by pattern of development –Cleavage pattern: Spiral, determinate cleavage (Protostomes) Radial, indeterminate cleavage (Deuterstomes) –Coelom formation Schizocoelous body cavity (mesoderm splits) Enterocoelous body cavity (mesoderm folds –Fate of Blastopore Mouth develops from blastopore (Protostomes) Anus develops from blastopore (Deuterostome)