Unit 8 Chapter 25 What is an animal?

Characteristics of Animals 1) They are multicellular 2) They are heterotrophs (consumers) Motility = most animals use locomotion to find their food sources Sessile = organisms that are permanently attached (don’t spend much energy to obtain food) Sponges are sessile animals

Characteristics of Animals 3) They injest their food 4) They have specialized cells, tissues, organs, & systems Ex: the complex digestive tract of the earthworm

Characteristics of Animals 5) They have similar stages of development: Blastula Fluid-filled ball formed from many cell divisions Gastrula Blastula folds inward to form two layers

Gastrulation Formation of a cavity of two or more layers with an opening at one end 1) Ectoderm = outermost layer 2) Endoderm = innermost layer Higher animals have a third, middle layer: 3) Mesoderm = develops into muscles, etc 1 2 3

Symmetry the arrangement of body structures 1) Radial symmetry Can be divided along any plane, through a central axis, into roughly equal halves

2) Bilateral symmetry Can be divided down its length into similar right & left halves Has a definite front (anterior,) rear (posterior), top (dorsal,) and belly side (ventral)

Body plans Acoelomates Develop from 3 cell layers, but have NO body cavity Ex: flatworms

Body plans Pseudocoelomates A fluid=filled body cavity only partially lined with mesoderm Ex: Roundworms

Body plans Coelomates Has a fluid-filled body cavity completely surrounded by mesoderm Ex: segmented worms & all higher animals

Animal Diversity Invertebrates Animals without backbones Often having exoskeletons outside their body for framework & support

Animal Diversity Vertebrates An animal with an endoskeleton & a backbone Endoskeletons are internal frameworks that provide protection, support, & muscle attachment Ex: fishes, amphibians, reptiles, birds & mammals