Chapter 24 Introduction to Animals
Section 1: Animal Characteristics
Section 2: Animal Body Plans
Section 3: Sponges and Cnidarians
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Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Evolution of Animal Body Plans
 Anatomical
features in
animals’ body
plans mark the
branching
points on the
evolutionary
tree.
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Evolution of Animal Body Plans
 Relationships on
this tree are
inferred by
studying
similarities in
embryological
development and
shared anatomical
features.
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Symmetry
 Similarity or balance among body structures of organisms
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Symmetry
TYPES OF SYMMETRY
 Asymmetry – No tissue and irregular in shape
 Radial symmetry –
 Has a top and a bottom but no sides
 Can be divided on multiple planes
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Symmetry
TYPES OF SYMMETRY
 Bilateral symmetry –
 Can be divided on one plane to show a mirror image
on each side.
 Has a top, bottom and sides.
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Cephalization
 Animals with bilateral symmetry tend to
have a posterior (tail-end) and anterior
(head-end).
 They also have a tendency to concentrate
nervous tissue and sensory organs at the
anterior end of the animal
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Coelomates
 Have a fluidfilled cavity with
tissue formed
from mesoderm
that lines and encloses the organs in the
coelom
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Pseudocoelomates
 Have a fluid-filled
body cavity that
develops between
the mesoderm and
the endoderm rather than developing
entirely within the mesoderm
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Acoelomates
 Have solid bodies
without a fluid-filled
body cavity
between the gut
and the body wall
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Development in Coelomate Animals
Protostomes
 The mouth develops from the first opening in
the gastrula.
Deuterostomes
 The anus develops from the first opening in
the gastrula.
Chapter 24 Introduction to Animals
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Segmentation
 Segmented animals can be “put together”
from a succession of similar parts.
 Can survive damage to one segment
 Movement is more effective