1. Infer How is the embryology of echinoderms similar to that of vertebrates? What might this similarity indicate about their evolutionary relationship

2. Review What two features define animal phyla3. Apply Concepts Explain the description of a body

plan as an evolutionary “experiment” be sure to include successful and unsuccessful body plans

CH 25 INTRODUCTION TO ANIMALS25.2 Animal Body Plans and Evolution

Features of Body Plans

Levels of organization Body symmetry Differentiation of germ layers Formation of body cavities Patterns of embryological development,

segmentation, cephalization, and limb formation.

Levels of Organization

Body Symmetry

Radial symmetry Body parts extend from a

central point Many lines of symmetry.

Body Symmetry Bilateral symmetry

Single imaginary plane divides the body into left and right sides that are mirror images of one another

Have a definite front (anterior) and a back (posterior)

Have an upper (dorsal), and a lower (ventral).

Differentiation of Germ Layers

Endoderm innermost germ layer Develops into lining of the digestive tract and much of

the respiratory system Mesoderm

Middle germ layer Gives rise to muscles and much of the circulatory,

reproductive, and excretory organ systems.

Differentiation of Germ Layers

Ectoderm Outermost germ layer Produces sense organs, nerves, and the outer layer of

the skin.

Formation of a Body Cavity

Body cavity Fluid-filled space between the digestive tract and

body wall Provides a space in which internal organs can be

suspended and grow.

Coelomate

True coelom Body cavity that develops

within the mesoderm and is completely lined with tissue derived from mesoderm.

Acoelomates

Lack a body cavity altogether.

Pesudocoelomate

Pseudocoelom Only partially lined with

mesoderm.

Patterns of Embryological Development

Zygote Fertilized egg, sexual

reproduction Blastula

Hollow ball of cells Develops from zygote.

Blastula develops

Folds in on itself, forms an elongated structure with a tube that runs from one end to the other

Tube becomes the digestive tract.

Protostomes Blastopore becomes the mouth Anus forms from a second opening at the opposite end

of the tube Most invertebrates.

Deuterostomes Blastopore becomes the anus Mouth is formed from a second opening that develops Chordates and echinoderms.

Segmentation: Repeating Parts

Typically have at least some internal and external body parts that repeat on each side of the body.

Cephalization: Getting a Head

Cephalization Concentration of sense organs and nerve cells at their

anterior end Formed by the fusion of internal and external parts

that concentrate sense organs and nerve cells in the head.

Limb Formation: Legs, Flippers, and Wings

Segmented, bilaterally symmetrical animals typically have external appendages on both sides of the body.

Animal phyla are typically defined according to adult body plans and patterns of embryological development.

The Cladogram of Animals

Indicates the sequence in which important body plan features evolved.

Complicated body systems of vertebrates aren’t necessarily better than the “simpler” systems of invertebrates.

1. Which animal takes the most time to reach the differentiation stage and which takes the least time

2. How much longer does it take a rhesus monkey zygote to reach the 4 cell stage than a chicken zygote

3. Which developmental stage would you expect to occur first- formation of the coelom or the blastula- explain