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Characteristics already discussed in Biology II:
1. Animals are multi-cellular and eukaryotic (have a nucleus)
- Levels of organization in a multi-cellular organism
o Cell – Tissue – Organ - System
- Specialization: the evolutionary adaptation of a cell for a particular function
o Multi-cellular organisms have specialized cells
- Division of labor = efficiency
- Enables organisms to evolve and adapt to many environments
o Uni-cellular organisms must do all functions, no specialized cells b/c it is the only cell
2. Animals lack cell walls
3. Animals are heterotrophic feeders: most use ingestion
“new” characteristics that apply to all Animals
4. Animals are often classified as
o vertebrates – have a backbone
o invertebrates – do NOT have a backbone
5. Most animals reproduce sexually, some asexually
o Sexual reproduction = two gametes fuse to form a zygote
o Development leads to differentiation (cells becoming specialized)
6. Most animals have independent movement
o nervous/muscle tissue (tissue only found in animals)
7. Animals form a blastula during embryonic development
The first animals probably arose in the sea
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Invertebrates: (Absence of a backbone)
• Greatest # of animal species (more than 95%; Most individual animals alive today)
• Probably evolved from heterotrophic, colonial protists (independent repro. cells & specialization)
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Chordates: animals with a notochord
• Notochord: firm/flexible rod of tissue on the dorsal part of the body
• Dorsal nerve cord: hollow tube above the notochord
• Pharyngeal pouches: part of the digestive tract
• Postanal tail: muscle tissue at posterior opening of the digestive tract
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A few chordates retain these characteristics all their lives
In most vertebrates (which is a subphylum of chordates):
• The dorsal nerve cord develops into the brain & spinal cord
• The notochord is replaced by the backbone
• In aquatic vertebrates the pharyngeal pouches evolved into gills
Biology II – Chapter 32 Notes: Introduction to Animals
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This phylogenetic diagram represents a hypothesis for the relationship among members of the
animal kingdom based on rRNA analysis. Look at tissues, symmetry & embryo development!
Body Structure: Patterns of Symmetry
Body Symmetry: arrangement in which parts that lie on opposite sides of an axis are identical
• Results from the animal’s pattern of development
3 types of body symmetry include:
1. Asymmetry
• Do not display symmetry (no equal sides)
• Ex: Sponges, Coral
2. Radial Symmetry
• Parts are organized in a circle around an axis
• Have a top/bottom but no front/back or left/right (several places to divide in half equally)
• Ex: Starfish, Hydra, Sea Anemone
3. Bilateral Symmetry
• Have 2 similar halves on either side of axis; have a left/right
• Cephalization: concentration of sensory/brain in anterior end
• Ex: Human, Butterfly, Squirrel
Biology II – Chapter 32 Notes: Introduction to Animals
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Review of Basic Symmetry Terms
•Anterior –toward the head end of the body
•Posterior –toward the tail end of the body
•Ventral –toward the belly
•Dorsal –toward the back
Additional Terminology Review:
• Anterior/cranial/rostral/cephalic/cephalad-towards the front or head
• Posterior/caudal/caudad-towards the rear or tail
• Dorsal-towards the top of the body, near the spinal cord
• Ventral-towards the belly or underside of the body
• Lateral-towards the sides of the body
• Medial-towards the middle of the body or midline
• Proximal-near the base of a structure
• Distal-further away from the base of a structure
Plane Terminology
where you may make a cut or be expected to look for a structure
•Frontal plane –vertical cut;
divides organism into front & back
•Sagittal plane –vertical cut;
divides organism into left & right sides
•Transverse plane –horizontal cut;
divides organism into top & bottom
Biology II – Chapter 32 Notes: Introduction to Animals
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Body Structure: Germ Layers
fundamental tissue types found in the embryos of all animals except sponges
•EVERY organ and tissue arises from a germ layer
•Diploblastic- 2 layers of tissue separated by a mesoglea layer
(Ctenophores & Cnidarians)
•Ectoderm: outer protective tissue & sensory
•Endoderm: inner tissue lining
•Triploblastic- 3 tissue layers (all other phyla)
• Ectoderm: skin, nervous tissue
• Mesoderm: muscles (motion), skeletal, reproduction, transport (circulatory) &
excretion
• Endoderm: throat passage: leads to the lungs & lining of digestive tract;
spleen, pancreas
Body Structure: Relatedness
how do all animals relate to each other and other organisms
• For classification, Biologists (& Taxonomists) use
– Both extant (living) & extinct (all dead) species
• Similarities in body plans
• Patterns of development
– All this information is used to create phylogenetic trees or diagrams
• Organisms on the same branch (flatworms & rotifers) are more closely related than
to other animals
– Have similar morphology
– Have similar rRNA sequences
– New ways to classify or organize organisms are already being done!
– GENE SEQUENCING
– GENE MAPPING
– DNA ANALYSIS
– This continues to change how organisms are classified…
Biology II – Chapter 32 Notes: Introduction to Animals
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Section 2: Invertebrate Characteristics
• Symmetry:
– Radial – jellyfish, floats and takes in stimuli from all directions
– Most are bilateral – adaptation for a motile lifestyle & cephalization
•
Segmentation: repeating units (worm) or not (insect)
•
Support of the Body: fluid filled cavity (roundworm) or exoskeleton
•
Respiratory/Circulatory System: gas exchange (O in, CO out)
2
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2
In simple inverts gas exchange occurs directly across membranes (no system)
In aquatic arthropods & mollusks, gills are specialized organs for gas exchange
Open: blood from heart/vessels to cavity, then vessels (arthropods & some mollusks)
Closed: blood from heart circulates through body in vessels (annelids & other mollusks)
•
Digestive & Excretory System:
– In sponges = digestion occurs within cells
– In cnidarians = there is a central chamber with 1 opening
– Most have a digestive tract or “gut” running through the body
– Most have specialized structures to reabsorb water before waste is excreted (primitive
kidneys)
•
Nervous System:
– Sponges don’t have neurons; some cells do respond to environment
– Neurons evolved in cnidarians
– Mollusks is where cephalization is shown (evidence of a brain!)
– Organization ranges, described as a “net” or system
•
Reproduction & Development:
– Most reproduce sexually, some asexually
– Some are hermaphrodites: produces BOTH male and female gametes
– Indirect development: have intermediate larval stage (most inverts)
• Larvae usually eat different things than adult increasing survival
– Direct development: young similar to adult
Types of Invertebrate Development
Indirect Development
(young have a completely different appearance)
Biology II – Chapter 32 Notes: Introduction to Animals
Direct Development
(young appear similar, just smaller)
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Section 2: Vertebrate Characteristics
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•
•
•
Vertebrates are chordates that have a backbone
Classes include fish, amphibians, reptiles, birds and mammals
All classes (except fish) spend part/all of their life on land
Characteristics are usually adaptations to life on land
– Support of the body
– Conservation of water
• Symmetry: bilateral
• Segmentation: repeating structures of ribs & vertebrae
(vertebrae = repeating bony units of the backbone)
• Support of the Body:
– endoskeleton: an internal skeleton made of bone and cartilage; including the backbone
• Body Coverings: integument = the outer covering
– Adapted to moist environments: fish
– Adapted to dry environments: watertight
– Protection (scales of land animals) or Respiration (amphibians)
• Respiratory & Circulatory System:
– Gills are used for gas exchange in fish and larval amphibians
– Lungs are used for gas exchange in all terrestrial vertebrates
– Vertebrates have a closed circulatory system
• Multi-chambered hearts developed = more efficient because oxygenated blood is
separated from deoxygenated blood
– Digestive & Excretory System:
– The gut (mouth – anus) can be long and folded, increasing surface area for more absorption
of nutrients (humans = about 23 feet long)
– Kidneys filter waste from blood while reabsorbing water
– Nervous System: highly organized brains
• Reproduction & Development:
– External fertilization: sperm & egg meet outside the body (many fish & amphibians)
– Internal fertilization: sperm & egg meet inside the body
• Eggs develop outside the body (lay eggs) (many fish amphibians, reptiles, birds)
• Eggs develop inside the body until ready to hatch (some fish, amphibians, reptiles)
• Give birth to live young (mammals)
Biology II – Chapter 32 Notes: Introduction to Animals
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Section 3: Fertilization & Development
Fertilization: union of female & male gametes to form a zygote
• Male gamete = sperm
– Specialized for movement; streamlined and small
Head contains chromosomes, tail is a long flagellum
• Female gamete = egg
– Typically large b/c it has a large store of cytoplasm & yolk
– size of the egg depends on how long the species needs the yolk supply to last
Fertilization:
• The sperms cell membrane fuses with the egg cell membrane
– This causes an electrical change in the egg membrane blocking other sperm
• The nucleus of the sperm enters the egg’s cytoplasm
• The sperm & egg nuclei merge forming the diploid nucleus of the zygote
• Now replication begins and the first cell division can occur! 
Cleavage & Blastula Formation
– Cleavage: the series of cell divisions that occur
immediately following fertilization
– The # of cells increase, not the size of each cell
– Eventually a hollow blastula is formed
Gastrulation & Organogenesis
– As the organism develops, the blastula “collapses” and the sides fold inward.
This is called gastrulation
– As folding continues, the archenteron develops (primitive gut)
– This helps to define the germ layers (endo, meso, & ectoderm)
– Organogenesis: the process where each of the germ layers develops into certain organs
Biology II – Chapter 32 Notes: Introduction to Animals
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Patterns of Development: Types of Body Cavities
Most animals have some type of body cavity (a fluid-filled space that forms between the
digestive tract and the outer wall of the body during development
Animals with 3 body layers divided into 3 categories:
•Acoelomates: have no space between layers
•Ex: Platyhelminthes (Flatworm)
•Pseudocoelomates: fluid-filled pseudocoel b/w layers; providing internal support
•Ex: Rotifers & Nemotodes (Roundworms)
•Coelomates: have a fluid-filled space in the mesoderm (coelom), allowing organs to move
independently; providing internal support
•2 ways these develop
•Protostome- mouth develops 1st, anus 2nd
•Deuterostome- anus develops 1st, mouth 2nd
•Ex: Pigs
Kingdom Animalia
•The Animal Kingdom contains the most species!
(over 1 million known & about 1 million undiscovered)
We will study 11 of 30+ Phyla
•6 Lower Invertebrate Phyla
•sponges, jellyfish, some worms
•4 Higher Invertebrates Phyla
•snails, insects, starfish
•1 Vertebrate Subphylum (subphylum of Chordata)
•5 Classes: fish, birds, reptiles, amphibians, mammals
Biology II – Chapter 32 Notes: Introduction to Animals
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