Animal Characteristics Heterotrophs – must ingest others for nutrients Multicellular – complex bodies No cell walls – allows active movement Sexual reproduction – no alternation of generations – no haploid gametophyte

9 Major Phyla of the Animal Kingdom

Porifera Cnidaria Platyhelminthes spongesjellyfishflatworms roundworms Nematoda MolluscaArthropodaChordata AnnelidaEchinodermata mollusks multicellularity Ancestral Protist tissues bilateral symmetry body cavity segmentation Animal Evolution coelom starfishvertebrates endoskeleton segmented worms insects spiders backbone specialization &  body complexity specialized structure & function, muscle & nerve tissue distinct body plan; cephalization  body complexity  digestive & repro sys  digestive sys  body size redundancy, specialization,  mobility  body & brain size,  mobility radial bilateral

Animals show distinctive ‘body plans’ Asymmetry – no pattern – sponges Radial Symmetry  – some sponges and – sea anemone –no head or sides Bilateral symmetry – Usually show cephalization – Often move from place to place – crayfish/human

“It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.” Lewis Wolpert (1986) The development and arrangement of the basic embryonic layers (ectoderm → skin and nervous system, mesoderm → muscle and bone, and endoderm → digestive tract) establishes the basic body plan.

Tissue Organization SPONGES – have no true tissues – Animal body plans vary in organization of tissues –Sponges lack true tissues –In other animals, cell layers formed during gastrulation give rise to tissues and organs –Some animals have only ectoderm and endoderm, but most animals also have mesoderm –ectoderm → skin and nervous system –endoderm → digestive tract –mesoderm → muscle and bone, and circulatory system

Body Cavity also used to characterize organisms – The body cavities of animals vary –Flatworms have a solid body and lack a coelom –A pseudocoelom is partially lined by tissue derived from mesoderm –A true coelom is completely lined by tissue derived from mesoderm Connecting structures called mesenteries connect inner tissue to outer tissue and suspend internal organs. Only found in true coelomates

No coelom  Flatworms= acoelomates  Pseudocoelom nematodes True Coelom  Annelids and higher organisms

INVERTEBRATES Animals that lack backbones Occupy almost every habitat on Earth! They make up 97% of all animals