Characteristics of animals
- Are Heterotrophic
- Use oxygen for respiration
- Do not have a cell wall
- Have specialized cells:
occurs during embryonic development, where cells begin to differentiate from one another to perform specific functions - Have nerve cells (with the exception of the Porifera phylum)
What is developing embryo, and three layers
Three layers of cells form during embryonic development, called germ layers:
- Endoderm
- Ectoderm
- Mesoderm
Ectoderm
Outer layer, develops into skin and nervous system
Endoderm
Inner layer, develops into the inner lining of internal systems
Mesoderm
Middle layer, develops into the circulatory, reproductive, excretory, and muscular systems
Two key divisions of animals
- Radial symmetry
- Bilateral symmetry
Radial symmetry
- Symmetry around a central axis
- Only found in phylum Cnidaria
- Ex. Jellyfish
Bilateral symmetry
- Symmetry around a midline
- Ex. Humans
Branches of bilateral symmetry
- Protostomes
- Deuterostomes
Protostomes
- Mouth forms before the anus in embryonic development
- Are Invertebrates
Deuterostomes
- Anus forms before the mouth in embryonic development
- Can be vertebrates or invertebrates
Protostome invertibrates
- Arthropoda
- Nematoda (roundworms)
- Annelida (segmented worms)
- Mollusca
- Rotifers
- Platyhelminthes (flat worms)
Arthropoda
- Examples are Insects and spiders
- Segmented with jointed appendages
- Antennae – sensory system
- Exoskeleton made of chitin
Nematoda (round worms)
- Examples are Dog Heartworms
- Unsegmented, cylindrical bodies, with complete digestive tracts
Annelida (segmented worms)
- Examples are earthworms
- True digestive track (goes in one end comes out the other)
Mollusca
- Examples are helix and octopus
- Many have hard shell made of calcium carbonate
Rotifers
- Example is a Rotifer
- Aquatic, use cilia to direct food to mouth
Platyhelminthes (flatworms)
- Examples are tapeworms
- Flattened, unsegmented
- Single opening for digestive cavity.
Deuterostomes Segments
- Vertebrates
- Invertebrates
Deuterostome invertebrates
- Echinoderms
- Example is a starfish
Deuterstome vertebrates
- Phylum = chordata!
- Have the presence of a backbone, which protects their dorsal nerve cord (spinal cord in humans)
- Most also have a cranium (skull) that protects the brain, which also connects to the nerve cord
- Have advanced organ systems and exhibit complex behaviors
There are 5 vertebrate classes: - Fish
- Amphibians
- Reptiles
- Birds
- Mammals
Special cases
Porifera
- Example is a sponge
- No symmetry
- No specialized tissue
Cnidaria
- Example is a jellyfish
- 2 germ layers
- 1 hole (mouth and anus)
- No organs
How eukaryotic cells developed into multicellular organisms
- Spherical arrangement of cells in a colony might have become indented, forming a hollow cavity which became a cavity that specializes in digestion
- The cells became specialized and formed feeding cells which used the hollow cavity to capture and digest food.
- The cells outside the hollow cavity specialized in other areas as they were not needed for digestion
- We can see similar arrangements and processes occurring in certain animals today.
- This idea of cells becoming specialized to fit their environment and needs is how lots of our cells were formed.
