1.
Which numbers
represent
chordates and
which numbers
represent
invertebrates?
5.
2.
3.
4.
6.
7.
25.2 Animal Body Plans and
Evolution
Features of Body Plans
• Each animal phylum has a unique organization of
particular body structures that is often referred to as a
body plan.
• Features of body plans include:
–
–
–
–
–
–
–
–
Levels of organization
Body symmetry
Differentiation of germ layers
Formation of body cavities
Patterns of embryonic development
Segmentation
Cephalization
Limb formation
Levels of Organization
• Animals have specialized cells that are organized into
tissues.
• There are several types of tissues found in animals:
– Epithelial tissues- cover body surfaces inside and out,
are also thin and flat.
• Example: epithelial tissues line lungs and allow gases
to easily diffuse through
– Muscle tissues
– Connective tissues
• Tissues combine during growth and development to form
organs and organ systems to carry out complex functions
Body Symmetry
• Bodies of most animals exhibit some sort of
symmetry
• There are two different forms of symmetry
– Radial symmetry: any number of imaginary planes
drawn through the center of the body could divide into
equal halves. Example: Sea anemone
– Bilateral symmetry: a single imaginary plane divides the
body into left and right sides that are mirror images of
each other.
• Animals with bilateral symmetry have the following
–
–
–
–
A definite front: also known as the anterior
A definite end: also known as the posterior
An upper side: also known as the dorsal side
A lower side: also known as the ventral side
Differentiation of Germ Layers
• During embryological development the cells of
most animal embryos differentiate into 3 germ
layers
– 1. Endoderm: the innermost germ layer, develops
into linings of the digestive tract and much of the
respiratory system
– 2. Mesoderm: the middle layer, gives rise to the
muscles and much of the circulatory, reproductive,
and excretory organ systems
– 3. Ectoderm: the outermost layer, produces sense
organs, nerves, and the outer layer of skin
Formation of a Body Cavity
• Most animals have a body cavity, which is a fluid-filled space between the
digestive tract and body wall
• Body cavities provide space for internal organs to suspend and room for
organs to grow
• Most complex animal phyla have a true coelom- a body cavity that develops
within the mesoderm and is completely lined with tissue derived from the
mesoderm
• The coelom wraps around the gut and internal organs are suspended in it
• Animals with a coelom allows the animals to move without damaging the
internal organs or interfering with the organ’s function
• Acoelomates are invertebrates that lack a coelom
• The are of an acoelomate’s body wall and gut is completely filled with
tissues
• Some invertebrate groups have a pseudocoelom, which is only partially
lined with mesoderm
• This false coelom is filled with liquid that can act like a skeleton and
provide support
Patterns of Embryological
Development
• Every animal that reproduces begins
as a zygote (a fertilized egg)
• At the beginning of development a
zygote forms a blastula, which is a
hollow ball of cells like an inflated
balloon
• The blastula develops into the
digestive tract by folding in on itself
and developing a long elongated tube
that runs from one end to the other
• In the beginning the digestive tract has
only one opening, called the
blastopore
Patterns of Embryological
Development
• An efficient digestive system needs two openings: a
mouth through which food enters and an anus through
which waste exits
• Protostomes: the blastopore becomes the mouth and
the anus becomes the second opening, which develops
at the opposite end of the tube
• Examples: flatworms, earthworms, snails, clams, spiders,
and insects
• Deuterotomes: the blastopore becomes the anus, and
the mouth is formed from the second opening that
develops
– Chordates and echinoderms (sea stars) are deuterotomes,
which indicates that echinoderms are closely related to
chordates
Segmentation: Repeating Parts
• Segmentation occurs as many bilateral
symmetrical animals develop, their bodies become
divided into numerous repeated parts, or
segments
• Segmented animals such as worms, insects, and
vertebrates have at least some internal and
external body parts that repeat on each side of the
body
• The most successful animals, including humans,
have bilateral symmetry and segmentation
Cephalization: Head Formation
• Animals with bilateral symmetry typical exhibit
cephalization- the concentration of sense organs and
nerve cells at their anterior end
• The most successful animals including arthropods and
vertebrates exhibit pronounced cephalization
• Insect and vertebrate embryos heads are formed by
fusion and specialization of several body segments during
development
– As the segments fuse the external and internal parts combine
in ways that concentrate sense organs in the head, such as
the eyes
– Nerve cells that process information and “decide” what an
animal should do are also found in the head
– Animals with a head move in a head first direction because
this way the concentration of sense organs and nerve cells
come in contact with the new environment first
Limb Formation: Legs, Flippers, and
Wings
• Segmented, bilaterally symmetrical animals
typically have appendages on both sides of the
body.
• The types of appendages vary depending on the
animal. Examples:
• Bristles in worms
• Jointed legs in spiders
* Flippers in dolphins
* Wings in dragonflies
• These different kinds of appendages have evolved
several times, and have been lost several times, in
various animal groups
• Limb formation and segmentation have evolved to
allow animals to be more flexible and have
improved movement
Limb Formation: Legs, Flippers, and
Wings
Animal Type:
Levels of organization
Cells, tissues, organs?
Body symmetry
Germ layers
Body Cavity
Bilateral, radial?
1,2,3..?
Coelom, Pseudocoelom,
Acoelom..?
Embryological Development
Segmentation
Cephalization
Protostomes, Deuterostome
Absent, Present?
Present, Absent?
Animals to include on chart:
•Sponges
*Cnidarians
•Flatworms
*Roundworms
•Annelids
*Mollusks
•Arthropods
*Echinoderms
•Chordates
Cnidarians
Levels of
organization
Body symmetry
Germ layers
Specialized cells,
Tissues
Radial symmetry
Two
Body Cavity
Embryological
Development
Segmentation
Acoelomate
___
Cephalization
Absent
Absent
25.2 Body Plans and Evolution
Vocabulary
• Radial Symmetry: any number of imaginary planes drawn
through the center of the body could divide into equal halves.
• Bilateral Symmetry: a single imaginary plane divides the body
into left and right sides that are mirror images of each other.
• Endoderm: the innermost germ layer, develops into linings of the
digestive tract and much of the respiratory system
• Mesoderm: the middle layer, gives rise to the muscles and much
of the circulatory, reproductive, and excretory organ systems
• Ectoderm: the outermost layer, produces sense organs, nerves,
and the outer layer of skin
• Coelom: a body cavity that develops within the mesoderm and is
completely lined with tissue derived from the mesoderm
25.2 Body Plans and Evolution
Vocabulary
• Pseudocoelom: which is only partially lined with mesoderm
• Zygote: a fertilized egg
• Blastula: a hollow ball of cells like an inflated balloon that
develops into the digestive tract by folding in on itself and
developing a long elongated tube that runs from end to the other
• Protostomes: the blastopore becomes the mouth and the anus
becomes the second opening, which develops at the opposite
end of the tube
• Deuterostomes: the blastopore becomes the anus, and the
mouth is formed from the second opening that develops
• Cephalization: the concentration of sense organs and nerve cells
at their anterior end
25.2 Assessment
• 1a. List eight features of animal body plans.
• 1b. How is the embryology of echinoderms
similar to that of vertebrates? What might this
similarity indicate about their evolutionary
relationship.