Download Introduction to Animals Section 3 Section 3

Introduction to Animals
Section 3: Evolutionary Trends in
Animals
Section 3
Introduction to Animals
Section 3
Key Ideas
• What evolutionary trends in body structure do animals
exhibit?
• What characterizes early embryonic development in
animals?
• What types of internal body plans do animals have?
• What two body characteristics gave animals a greater
ability to move and to be more flexible?
Introduction to Animals
Section 3
Tissues and Symmetry
• body plan
– Shape
– Symmetry
– internal organization
• more-complex through time including true tissues and
bilateral symmetry
Introduction to Animals
The Animal Body: An Evolutionary
Journey
Section 3
Introduction to Animals
Section 3
Tissues and Symmetry, continued
Tissues
• Tissues
– groups of cells that have the same structure and work together to
perform a specific function
• Organs
– different tissues working together to perform particular jobs
Introduction to Animals
Section 3
Tissues and Symmetry, continued
Symmetry
• Sponges are asymmetrical.
– No symmetry
• radial symmetry
– body parts arranged around a central axis.
• bilateral symmetry
– a plane that passes down the middle of the animal from head to
tail divides the animal into mirror-image halves
– Allowed specialized body parts
Introduction to Animals
Section 3
Tissues and Symmetry, continued
Symmetry, continued
• Cephalization
– anterior (head) concentration of sensory structures and nerves
Introduction to Animals
Section 3
Early Embryonic Development
• Most animals reproduce through sexual
reproduction.
• zygote is produced through the union of sperm
and egg
• Cleavage is a series of cell divisions that occur
immediately after an egg is fertilized
– cells do not grow
Introduction to Animals
Section 3
Early Embryonic Development, continued
• Blastula
– hollow ball formed as the end result of cleavage
– fluid-filled interior is called the blastocoel.
• Gastrulation
– transformation of the blastula into the gastrula or the formation of
the embryonic germ layers.
– a pocket is formed called the blastopore.
Introduction to Animals
Section 3
Early Embryonic Development, continued
Differentiation
• dividing cells become increasingly different from each other
• ectoderm
– form the outer layer of the body
– the sense organs
– and the nervous system
• endoderm
– gut
– respiratory system
– and many glands
• mesoderm
–
–
–
–
Skeleton
Muscles
circulatory system
organs of reproduction and excretion.
Introduction to Animals
Section 3
Visual Concept: Cleavage and Blastula
Formation
Introduction to Animals
Section 3
Origins of Animal Tissues and Organs
Introduction to Animals
Section 3
Early Embryonic Development, continued
Patterns of Development
• Gastrula pocket folds inward.
• This process changes the pocket into the gut of the
developing embryo.
Introduction to Animals
Section 3
Early Embryonic Development, continued
Patterns of Development, continued
• protostomes, the mouth develops from the end of the
embryo near the blastopore, anus develops at the
opposite end.
• Flatworms, earthworms, snails and clams, spiders and
insects, and their relatives are all protostomes.
Introduction to Animals
Section 3
Early Embryonic Development, continued
Patterns of Development, continued
• deuterostomes, the mouth develops from the end of the
embryo opposite the blastopore, anus develops at or near
the blastopore.
– Opposite of protostomes
– Evolved 650 million years ago
– First animal with endoskeleton
• Sea stars and their relatives and vertebrates and their
relatives are all deuterostomes.
Introduction to Animals
Patterns of Animal Development
Section 3
Introduction to Animals
Section 3
Body Cavities
• A coelom is a fluid-filled space that contains the internal
organs between the body wall and the gut.
• Humans and other vertebrates have a coelom.
• Animals with no body cavity are called acoelomates.
Flatworms are acoelomates.
Introduction to Animals
Section 3
Body Cavities, continued
• Segmented worms and all other more "advanced" animals
have a true coelom and are called coelomates.
• The gut and other internal organs of coelomates are
suspended within the coelom.
• The coelom allows an animal to move without damaging its
organs or interfering with their functions.
Introduction to Animals
Visual Concept: Body Cavity
Section 3
Introduction to Animals
Section 3
Segmentation and Jointed Appendages
• Segmentation is obvious in some animals, such
as earthworms or caterpillars.
• In other animals, such as vertebrates, the
segments are visible only during early
development.
• The muscles of vertebrates develop from
segments of tissue called somites.
Introduction to Animals
Section 3
Segmentation and Jointed Appendages,
continued
• Segmentation can allow great mobility and flexibility. For
example, an earthworm can tie its body in knots.
• A small change in an existing segment can produce a new
type of segment with a different function.
• Arthropods were the first animals to have jointed
appendages.
– Allows animals to perform complex movements
Introduction to Animals
Visual Concept: Segmentation
Section 3
Introduction to Animals
Section 3
Summary
• Through evolutionary time, animals have developed
more-complex body plans, including true tissues and
bilateral symmetry.
• The steps of early embryonic development in animals
include cleavage, blastula formation, and gastrulation.
• Animals with bilateral symmetry have one of three basic
kinds of internal body plans. The body plan may include
a body cavity, or coelom.
Introduction to Animals
Section 3
Summary, continued
• The evolution of body segmentation and jointed
appendages gave animals a greater ability to move and
to be flexible.