Unit 8Chapter 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