25.2_Animal_Body_Plans_and_Evolution

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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
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