Chapter 32 – Animal

Diversity

32.1 – Animals are multicellular, heterotrophic eukaryotes

with tissues that develop from embryonic layers

Animals have the following characteristics:

Multicellular heterotrophs

Most have muscle & nervous tissue

Most reproduce sexually, with a flagellated sperm & a large egg which unite to form a diploid ZYGOTE

The diploid stage dominates the life cycle

1.3 million living species

Vocab

Zygote

Fertilized egg

Cleavages

Successive mitotic cell divisions without cell growth between cycles

Blastula

Hollow ball of cells surrounding a cavity called the blastocoel

Gastrula

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

Ectoderm

The outer tissue layer

Endoderm

The inner tissue layer

Blastopore

Opening into the gastrula

Becomes the mouth in protosomes

Becomes the anus in deuterostomes

Archenteron

Blind pouch formed by gastrulation

Some animals have larvae

Immature form distinct from the adult stage they will undergo metamorphosis

Animals share HOX GENES

Unique family of genes that play important roles in development

Can produce a wide diversity of animal morphology

32.3 – Animals & Their “Body Plans”

Symmetry

None (sponges)

Radial

Bilateral

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

Tissues

Animal body plans vary according to the organization of the animal’s tissues

Tissues are collections of specialized cells isolated from other tissues by membranous layers

During development, three germ layers give rise to the tissues and organs of the animal embryo

Ectoderm is the germ layer covering the embryo’s surface

Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron

Mesoderm is the middle layer

Diploblastic animals have ectoderm and endoderm

Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians

Body Cavities

Most triploblastic animals possess a body cavity

3 types:

1) A coelomate possesses a true body cavity

Derived from mesoderm

Filled with fluid

Separates an animal’s digestive tract from the outer wall

Earthworms

2) Pseudocoelomate

Triploblastic animals

Cavity formed from mesoderm & endoderm

Roundworms

3) Acoelomates

No cavities between alimentary canal & outer wall of body

Flatworms

Functions of Body Cavities

1) Cushion suspended organs

2) Act as a hydrostatic skeleton

3) Enable internal organs to grow & move independently

Protostome & Deuterostome

Development

3 major differences:

1) Cleavage

2) Coelom formation

3) 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