The document discusses trends in animal evolution from simple to complex organisms. It describes the nine major phyla of animals and their key characteristics. More complex animals tend to have specialized cells, tissues, organs and organ systems, bilateral symmetry, a head with sensory organs, a fluid-filled body cavity, and complex embryo development. The functions of feeding, respiration, circulation, excretion, response, movement and support, and reproduction are examined among different invertebrate groups.

1. The Animal Kingdom

2. What is an animal?
• Multicellular
• Eukaryotic
• Heterotrophic
• No cell walls
• 95% of all animals are “invertebrates.”

3. Trends in Animal Evolution
• Our survey of the animal kingdom will
start with simple animals and move to
more complex ones.
• We will investigate “invertebrates” first
and “vertebrates” later.
• Invertebrates- animals without a
backbone
• Vertebrates- animals with a backbone

4. Animal Phyla
• There are nine major phyla of animals…
M 1. Poriferans (sponges)
o
r 2. Cnidarians (jellyfish)
e 3. Flatworms (tapeworm)
4. Roundworms (heartworm) Invertebrates
c
o 5. Annelids (earthworm)
m 6. Mollusks (clam)
p 7. Arthropod (grasshopper)
l
e 8. Echinoderm (starfish)
x 9. Chordate (human)

5. Animal Evolutionary
Relationships

7. Trends in Animal Evolution
• Complex animals tend to have…
1) Specialized cells  Tissues  Organs 
Organ Systems
2) Bilateral Symmetry (no symmetry  radial
 bilateral)
3) Cephalization (head with sensory organs)
4) Body cavity called coelom (acoelomate 
pseudocoelomate  coelomate)
5) Complex embryonic development

8. Trend #1: Cell Specialization and
Internal Body Organization.
• The more complex the animal, the more
“specialized” its cells become.
• Cells  Tissues  Organs  Organ system.
• Some animals have no organs- sponges
• Some animals have simple organs for
excretion and reproduction – flatworms
• Some animals have organ systems - mollusks

9. Trend #2: Body Symmetry
• With the exception to sponges, every animal
exhibits one of two types of body symmetry:
1. Radial symmetry
2. Bilateral symmetry

10. Radial Symmetry
• Imaginary plane can pass through a central axis
in any direction and body parts repeat around
center of organism’s body

11. Bilateral Symmetry
• Single plane can divide the body into two
equal halves.
• Animals with bilateral symmetry have a right
and left side, front and back, top and
bottom, and usually have segmented bodies.

12. Trend #3: Cephalization
• Animals with bilateral symmetry have a definite
head.
• Cephalization is the concentration of sense
organs and nerve cells in the anterior end (front
end) of the body.
• Animals with this trait tend to respond in more
complex ways to their environment.

13. Trend #4: Body Cavity Formation
• Most animals have a body
cavity called a “coelom.”
• Fluid-filled space between
the digestive tract and
body wall
• Think of this as the area
of your body where all of
your major organs are
located.
• Provides room for organs
to grow and expand.
• Less complex animals do
not have this area.

14. Types of Body
Cavity –
• Acoelomate
no body cavity,
3 germ layers all packed
together, gut completely
surrounded by tissues
• Pseudocoelomate –
fluid-filled cavity between
mesoderm and endoderm
(separates gut and body wall)
• Coelom –
fluid-filled cavity lined on both
sides by mesoderm, found
between muscles of body wall
and muscles around gut

15. Trend #5: Embryo Development
• In protostomes (worms, mollusks, and arthropods), blastopore
develops into mouth.
• In deuterostomes (echinoderms and chordates), blastopore develops
into anus.
• Three layers of embryonic cells (germ layers):
1. Endoderm – Develops into digestive and respiratory tracts.
2. Mesoderm – Develops into muscles, heart, sex organs, and
kidneys.
3. Ectoderm – Develops into brain, sense organs, and skin.

17. Invertebrate Physiology (form and function)
• To survive, all animals must perform the same basic
tasks (feed, digest, circulate
nutrients, respirate, excrete
wastes, reproduce, etc.)
• Each group of invertebrates has unique systems to
help perform some of these tasks.
• We will study a variety of these systems amongst a
variety of invertebrate groups.

18. Function #1 “Feeding and Digesting”
• All animals must feed and digest.
• Two main methods of digestion:
1. Intracellular digestion.
 Food is digested inside of cells.
 Sponges mainly do this.
2. Extracellular digestion
 Food is broken down outside of cells in special
digestive organs.
 Simpler animals have only one opening where food
enters and waste leaves (two way digestive tract).
 Complex animals have two separate openings a
mouth and anus (one way digestive tract).

19. Two way vs. One way digestive
tract
Mouth/Anus

20. Function #2 “Respiration”
• All animals must exchange O2 and CO2 with
the environment.
• Structures range from gills  lungs
• All respiratory organs have two basic
features:
1. Large surface area to come in contact with
air or water (the larger the better).
2. Organs must be moist (important for
diffusion of gases across cells).

21. Function #3: “Circulation”
• All cells in an animal must take in
oxygen/nutrients and give off CO2/waste.
• Simple animals do this through diffusion with
their environment.
• Complex invertebrates have hearts and blood
vessels.
• There are two types of circulatory systems:
1. Open system
2. Closed system

22. Open Circulatory System
• Common in arthropods.
• Blood leaves the system (vessles)

23. Closed Circulatory System
• Blood stays within vessels.
• Characteristic of
larger, more active
animals.
• More efficient form of
circulation.

24. Function #4: “Excretion”
• All animals must control…
1. The amount of water in their cells.
2. The amount of ammonia (NH3) that builds
up in the cells due to the breakdown of
amino acids. Ammonia is poisonous to cells.
• The process of controlling these two things
varies between aquatic and terrestrial
invertebrates.

25. Excretion (cont.)
Aquatic Invertebrates Terrestrial Invertebrates
• Sponge, cnidarians, and • Can use a variety of
some worms. specialized structures to
• Excess ammonia and eliminate excess water and
water is released through waste from cells.
diffusion. • Ex.) Annelids = “Nephridia”
▫ Nephridia converts
ammonia to urine.

26. Function #5: “Response”
• Invertebrates show three trends in the
evolution of their nervous systems:
1. Centralization
2. Cephalization
3. Specialization

27. • Hydra (Cnidarian) No
centralization, cephalization, or
specialization

28. • Flatworm
• More centralized.
• More cephalized.
• More specialized.

29. • Arthropods.
• Very centralized
• Very cephalized
• Very specialized

30. Function #6: “Movement and Support”
• Most animals use muscles to move, pump
blood, and perform other life functions.
• Muscles usually work together with some kind
of skeletal system (three different types);
1. Hydrostatic skeletons – Muscles push water.
Common in cnidarians and worms.
2. Exoskeletons – Outer skeleton made of chitin.
Common in arthropods.
3. Endoskeletons – Inner skeleton. Common in
echinoderms and vertebrates.

31. Function #7: “Reproduction”
• Some animals can reproduce asexually during
part of their life.
1. Binary fission (splitting in two).
2. Budding
• Most animals reproduce sexually during at
least part of their life (requires sperm and
egg).
• Male must fertilize the female.
1. External fertilization
2. Internal fertilization