Notes for Chapter 9:
Architectural Pattern of an Animal

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The following lecture notes will use the following conventions:
        Clicking on web links is "optional" but they will help illustrate
            points made in lecture and by the authors of your text
        The web is very visual, links will help you visualize
        I expect you to read the entire assigned chapter in the text
           unless I indicate particular assigned pages, e.g.,
           Ch. 9: 180-183, 189-194

        Review questions (RQ) refer to those at the end of indicated
           chapter, for example, RQ9:1 is the first review question
           for Chapter 9 (p. 194).
        Certain boldface text terms will be featured as Key Terms
        Certain animals will be a Featured Animal
        Certain events will be a Featured Event

           Introduction refers to the preamble on the first page of every

Chapter 9 Assignment:

Ch. 9: 180-183, 189-194, RQ9: 1, 2, 4, 10-13

Introduction: New Designs for Living
     Featured Animal: Cnidarian colonial soft coral,
          Dendronephthya sp.
          Links: 1 - 2 - 3

     Featured Event: Cambrian Explosion - large animals with
          skeletons appear in the fossil record quite "suddenly",
          within about 10 million
years about 540 million years
          ago. By the Middle Cambrian (520 Mya), all major animal
          groups were present, plus a few whose affinity is still
          debated. The most famous deposit of fossils from the
          Middle Cambrian is the Burgess Shale in Canada.
          Links: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8


1. About 32 "phyla" (distinctive groups) of animals

2. Most present over 500 Mya (based on Cambrian Era fossils)

3. Selection continues to act

4. Shared traits reflect common ancestry

5. These shared traits are hierarchically nested

9.1. The Hierarchical Organization of Animal Complexity

       Key Terms: Metazoa, tissue, nerve net, organs, organ systems

[a better title for this section: "Size Matters"

take-home message: We can recognize grades (similar trends) related to size increase]

A. Grades of Organization

1. Unicellular eukaryotes: small = simple

a. Perform all basic functions within cell

b. Vary mostly within cells including organelles

2. Metazoa = multicellular animals

a. Cells become specialized parts dependent on other cells

b. Some metazoans (sponges) have little cellular organization

3. One lineage evolved tissues with cells working closely together

4. Larger animals typically have tissues working together as organs

B. Complexity and Body Size

1. Large body size is associated with greater complexity

2. Large animals live in different world than small animals

a. Surface area increases with square of body length

    Volume increases with cube of body length

b. Small animals have higher surface area to volume ratio

c. Flat or convoluted bodies have higher surface areas

d. Internal transports systems shuttle nutrients, gases and waste

3. Common trend towards size increase within lineages ("Cope’s Law")

4. Large size can be good

a. Better buffering against environmental fluctuations

b. Both predators and prey benefit from large size

c. Costs less to maintain body temperature

d. Costs less to move same distance

e. Large size is not always good, for example large animals are
   often the first to go extinct in catastrophes, and small size generally
   allows animals to survive during tough times or to specialize on
   smaller food resources.

9.2. Extracellular Components of the Metazoan Body
    (skip for now - we will cover these later in lab)

       Key Terms: epithelium (we will mention these in the next lecture)

9.3. Animal Body Plans

  A. Animal Symmetry

       Key Terms: spherical vs. radial (or biradial) vs. bilateral symmetry,
        Bilateria (monophyletic group of animals that have bilateral


1. Spherical: any plane divides the body into mirrored halves

2. Radial: any plane passing through the longitudinal axis divides the body

a. Examples: Cnidaria and Ctenophora (Echinoderms as adults)

b. Biradial: e.g., anemones are radial except for elongate mouth

c. Quadraradial: e.g., jellyfish typically have 4 gonads

3. Bilateral: sagittal plane divides body into two mirror halves

a. Directional movement

b. One end is typically specialized as head (cephalization)

c. Other end is typically "tail" where waste is dumped


  B. Body Regions

       Key Terms: cephalization, anterior vs. posterior, dorsal vs.
        ventral, medial vs. lateral, proximal vs. distal, frontal vs.
        sagittal vs. transverse plane (as in section through body)

1. Anterior: head end; posterior: tail end

2. Dorsal: back side; ventral: belly side

3. Medial: midline of body; lateral: the sides

4. Distal: far from; proximal: near

5. Frontal plane: dorsal from ventral

6. Sagittal plane: right from left

7. Transverse plane (cross section): anterior from posterior

8. Vertebrates have specific terms

a. Pectoral: chest

b. Pelvic: hips

  C. Body Cavities

       Key Terms: coelom (most animals) vs. parenchyma (flatworms)

1. Coeloms

a. Only bilaterians have (provides space for 3D organs)

b. Coeloms typically fluid-filled spaces surrounding gut

c. Arrangement provides "tube-within-a-tube"

d. Coeloms (organs) typically mesoderm

e. Mesoderm middle layer between ecto- and endoderm

f. Coelom provides space for organs and surface area for exchange

g. Earthworms use coelom for burrowing (hydrostatic skeleton)

2. Some Bilaterians Lack Coeloms (acoelomate, e.g., flatworms)

a. Not necessarily ancestral (primitive) condition

b. Flatworms surround gut with mesoderm/ectoderm cells

3. Some bilaterians lack ‘true’ coeloms (pseudocoelomates)

a. Examples include nematodes (roundworms)

b. Again, not necessarily ancestral; coeloms can be lost

c. Various pseudocoelomates not necessarily closely related

d. Pseudocoelomates do have a cavity around the gut

e. This cavity traces back to the embryonic blastocoel

f. The cavity is not lined with mesoderm, as in "true" coelomates

4. Eucoelomate Bilateria

a. Could be ancestral condition, contrary to what is implied in text

b. Coelom is lined with mesodermal cell layer (peritoneum)

c. There are two distinct methods for coelom formation

1) Schizococoely: splitting of mesodermal cells

2) Enteroceoly: pouches derived from primitive gut

  (More on these later!)


  D. Segmentation, metamerism

       Key Terms: segmentation (repetition of somites) vs.
        metamerism (repetition of similar structures such as
        muscles, gills, or nerves)


1. Segmetation is serial repetition of similar body segments

2. Each segment a metamere or somite

3. True segmentation found in Annelida, Arthropoda and Chordata

4. Current evidence suggests each evolved it separately

5. Bilaterians generally can have metameric repetition of body parts

6. Current evidence suggests a "metameric" ancestral bilaterian

7. Terms segmentation/metamerism defined slightly differently in text

E. Cephalization
  Key Terms: cephalization, polarity

1. Differentiation of the head is most pronounced in bilaterians

2. Concentrated sense organs: efficient for sensing and responding

3. Activities generally start anterior, move posterior


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This page created 8/15/01 © D.J. Eernisse, Last Modified 8/24/01, Links Last Completely Checked 8/19/01