Ch 25 Introduction to Animals
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Transcript Ch 25 Introduction to Animals
1.
2.
3.
Infer How is the embryology of echinoderms
similar to that of vertebrates? What might this
similarity indicate about their evolutionary
relationship
Review What two features define animal phyla
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 ANIMALS
25.2 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.
2.
3.
Which animal takes the most time to reach the
differentiation stage and which takes the least time
How much longer does it take a rhesus monkey
zygote to reach the 4 cell stage than a chicken zygote
Which developmental stage would you expect to
occur first- formation of the coelom or the blastulaexplain