1. Introduction to Animals
Development, Symmetry, Tissues, Classification
AP Biology
Unit 6

2. Defining Characteristics of Animals
Multicellular
Heterotrophs
Sexual reproduction followed by development of body tissues and organs from layers of embryonic tissue
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3. Animal Development
Following fertilization, animal embryos develop in a systematic fashion
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4. Animal Development Cleavage Gastrulation
A series of rapid cell divisions
No time for cells to grow in between divisions
Gastrulation
Formation of layers of tissue that eventually develop into body parts and organs
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5. Body Symmetry 3 different categories of body symmetry
No symmetry (Asymmetrical)
Ex. Sponges (Porifera)
Radial symmetry
Bilateral symmetry
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6. Radial Symmetry One main axis in the center
No left or right sides– dividing the animal along any axis makes it a mirror image on each side.
Ex. Sea Anemones, Cnidarians (jellyfish)
Some radially symmetrical animals are slightly modified so that they aren’t fully symmetrical on all planes. They tend to move slowly or not at all. (Purves, 621)
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7. Bilateral Symmetry
Has a left and right side– only one plane will divide the animal so that the two sides are mirror images of one another.
Ex. Humans, fish, insects (most animals have bilateral symmetry)
Animals with bilateral symmetry also tend to move faster
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8. Directional Terms
There are certain directional terms that can be associated with bilateral symmetry
Dorsal = top side (think dorsal fin on dolphins)
Ventral = bottom side
Anterior = the end towards the head
Posterior = the end towards the tail
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9. Embryonic Germ Layers
Adult body parts develop from embryonic germ layers
There are 3 different germ layers
Ectoderm
Mesoderm
Endoderm
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10. Ectoderm Outermost layer
Develops into skin, nervous system, sensory organs
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11. Mesoderm
Middle layer
Develops into muscles, bones, circulatory system, excretory system, most of reproductive system
Not all animals have mesoderm
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12. Endoderm Inner most layer
Develops into the digestive system, respiratory system
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13. Diplo or triplo? Not all animals have all 3 germ layers
Diploblastic = only have 2 germ layers (no mesoderm, only endoderm and ectoderm)
Ex. Cnidarians (jelly fish)
Triploblastic = have all 3 germ layers
All bilaterally symmetrical animals (worms, birds, mammals, etc)
Closely linked to cephalization (concentration of nervous system and sensory organs close to head region)
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14. Body Cavities
Most animals have a body cavity (fluid filled space) between the endoderm and ectoderm
Coelom = body cavity lined with mesoderm
Type of body cavity influences how the animal moves
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15. Types of Body Cavities Acoelomate Lack an enclosed body cavity
Instead, the space is filled with cells
Ex. Flatworm
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16. Types of Body Cavities Pseudocoelomate
Have a fluid filled space in which many organs are suspended
Only one side (outer side) is lined with mesoderm (muscle)
Can’t control body shape as well since only one layer of muscle
Ex. Roundworm
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17. Types of Body Cavities Coelomate
Have a coelom – body cavity lined with mesoderm on both sides
Better control over movement since there are more muscles present (usually going in several different directions)
Ex. Earthworm, humans
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18. Protostomes vs. Deuterostomes
Excluding sponges, cnidarians and ctenophores, all other animals can be classified as either a protostome or a deuterostome.
Classification has to do with how the embryo develops.
Early in development a cavity forms
Blastopore = opening to the cavity
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19. Protostomes
Blastopore becomes the mouth of the animal (means “mouth first” in Greek)
Cleavage
Spiral = cleavage occurs in planes diagonal to the vertical
Determinate = The “fate” of each cell is determined very early
Examples include: molluscs, annelids (earthworms), arthropods
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20. Deuterostomes
Blastopore becomes the anus (means “mouth second” in Greek)
Cleavage
Radial = cleavage occurs along lines that are parallel or perpendicular to the vertical
Indeterminate = the “fate” of each cell is not determined until a little later (early cells can still become any type of cell– “stem cells”)
Examples include: Echinoderms, Chordates (have a backbone)
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21. Animal Classification
Based on developmental morphology
Molecular evidence suggests that this classification may not be entirely accurate
Common ancestor of all animals is thought to be a colonial protist with a flagella
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22. Animal Classification
“Basal” animal = porifera (sponge) = simplest animal; at the bottom of the evolutionary tree
Most animals have bilateral symmetry
All animals are thought to belong to a group called Metazoa
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23. Scientific Names for Animals
Porifera = sponges
Cnidarians = jellyfish
Platyhelminthes = flatworms
Nematodes = roundworms
Annelids = Earthworms
Arthropods = insects, crustaceans
Echinoderms = starfish
Chordates = humans, birds, fish, amphibians
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