1. 1. 2. 3.
Which numbers represent chordates and which numbers represent invertebrates? 4. 5. 6. 7.

2. 25.2 Animal Body Plans and Evolution

3. 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

4. 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

5. 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

7. 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

8. 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

10. 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

11. 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

13. 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

14. 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

15. 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 * Flippers in dolphins
Jointed legs in spiders * 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

16. Limb Formation: Legs, Flippers, and Wings

17. Levels of organization Cells, tissues, organs? Body symmetry
Animal Type:
Levels of organization
Cells, tissues, organs?
Body symmetry
Bilateral, radial?
Germ layers
1,2,3..?
Body Cavity
Coelom, Pseudocoelom, Acoelom..?
Embryological Development
Protostomes, Deuterostome
Segmentation
Absent, Present?
Cephalization
Present, Absent?
Animals to include on chart:
Sponges *Cnidarians
Flatworms *Roundworms
Annelids *Mollusks
Arthropods *Echinoderms
Chordates

18. Cnidarians Levels of organization Specialized cells, Tissues
Body symmetry
Radial symmetry
Germ layers
Two
Body Cavity
Acoelomate
Embryological Development
___
Segmentation
Absent
Cephalization

19. 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

20. 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

21. 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.