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

PoriferaCnidaria

Platyhelminthes

sponges jellyfish flatworms roundworms

NematodaMollusca Arthropoda Chordata

Annelida Echinodermata

mollusks

multicellularity

Ancestral Protist

tissues

bilateral symmetry

body cavity

segmentation

Animal Evolution

coelom

starfish vertebrates

endoskeleton

segmentedworms

insectsspiders

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 mesodermConnecting 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 CoelomAnnelids and higher organisms

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