Chapter 32 – Animal

Diversity

32.1 – Animals are multicellular, heterotrophic eukaryotes

with tissues that develop from embryonic layers

Animals have the following characteristics:Multicellular heterotrophsMost have muscle & nervous tissueMost reproduce sexually, with a flagellated sperm & a large egg which unite to form a diploid ZYGOTEThe diploid stage dominates the life cycle1.3 million living species

VocabZygote

Fertilized eggCleavages

Successive mitotic cell divisions without cell growth between cycles

BlastulaHollow ball of cells surrounding a cavity called the blastocoel

GastrulaAs the blastula is “punched in”, the embryonic tissue layers will form

EctodermThe outer tissue layer

Endoderm The inner tissue layer

BlastoporeOpening into the gastrula Becomes the mouth in protosomesBecomes the anus in deuterostomes

ArchenteronBlind pouch formed by gastrulation

Some animals have larvaeImmature form distinct from the adult stage they will undergo metamorphosis

Animals share HOX GENESUnique family of genes that play important roles in developmentCan produce a wide diversity of animal morphology

32.3 – Animals & Their “Body Plans”

SymmetryNone (sponges)RadialBilateral

Radial occurs in:- Jellyfish- Any cut

through the central axis would produce mirror images

Bilateral occurs in - Lobsters- Humans- Have a right & left side- Single cut would divide

the animal into 2 mirror image halves

- Dorsal side (back)- Ventral side (belly)- Anterior (head)- Posterior (tail)- Cephalization

TissuesAnimal body plans vary according to the organization of the animal’s tissuesTissues are collections of specialized cells isolated from other tissues by membranous layersDuring development, three germ layers give rise to the tissues and organs of the animal embryo

Ectoderm is the germ layer covering the embryo’s surfaceEndoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron

Mesoderm is the middle layer

Diploblastic animals have ectoderm and endodermTriploblastic animals also have an intervening mesoderm layer; these include all bilaterians

Body CavitiesMost triploblastic animals possess a body cavity

3 types:1) A coelomate possesses a true body cavity

Derived from mesodermFilled with fluidSeparates an animal’s digestive tract from the outer wallEarthworms

2) PseudocoelomateTriploblastic animalsCavity formed from mesoderm & endodermRoundworms

3) AcoelomatesNo cavities between alimentary canal & outer wall of bodyFlatworms

Functions of Body Cavities

1) Cushion suspended organs2) Act as a hydrostatic skeleton3) Enable internal organs to grow & move independently

Protostome & Deuterostome Development

3 major differences:1) Cleavage2) Coelom formation3) Fate of the blastopore

Cleavage:P = begins with spiral, determinate cleavageD = radial, indeterminate cleavage

Coelom Formation:Begins in the gastrula stage

P = coelom forms from splits in the mesodermD = coelom forms from mesodermal outpocketings of the archenteron

Fate of the Blastospore:P = mouth forms from the blastopore

D = mouth forms from a secondary opening