1. Typical Animal Characteristics
Characteristics animals have in common:
Multicellular, heterotrophic, and either move to get food or draw food toward them.
Sponges obtain food by filtering water and coral obtain food by using tentacles.
Organisms that don’t move from place to place are known as sessile organisms.
In flatworms there is only one opening—a mouth. An earth worm has two openings—a mouth and an anus.

2. *What are the early stages of development from zygote to gastrula?
After the zygote completes a series of continuous cell divisions, the result is a single layer of cells that form a hollow ball called the blastula. The blastula folds inward to form the gastrula, a hollow area surrounded by 2 cell layers.
The layer of cells on the outer surface of the gastrula is called the ectoderm.
The ectoderm cells of the gastrula continue to grow and divide into the skin and nervous tissue of the animal.
The layer of cells lining the inner surface of the gastrula is called the endoderm.
The endoderm cells develop into the lining of the animal’s digestive tract and into organs associated with digestion.

3. The mesoderm (“middle”) is the third cell layer found in the developing embryo between the ectoderm and the endoderm.
The mesoderm cells develop into the muscles, circulatory system, excretory system, and, in some animals, the respiratory system.
*Identify the 3 cell layers and give examples of the body organs and tissues that each layer gives rise to.
A protostome is an animal with a mouth that develops from the opening in the gastrula.
A deuterostome is an animal in which the anus develops from the opening in the gastrula.

4. An animal that is irregular in shape has a asymmetrical body plan.
Radial symmetry can be divided along any plane, through a central axis, into roughly equal halves.
Ex. Hydra, penny, starfish
Bilateral symmetry can be divided down its length into similar right and left halves that form mirror images of one another.
Ex. Butterfly, flatworm, fish
Animals with bilateral symmetry can find food and mates and avoid predators because they have sensory organs and good muscular control
Anterior-head end
Posterior-tail end
Dorsal-back
Ventral-belly

5. Animals that have 3 cell layers but no body cavities are called acoelomates
The organs of flatworms are embedded in the solid tissues of their bodies.
*Why are acoelomates so small?
In acoelomates, food and water move by diffusion. Therefore, no cell can be far from the exterior of the animal as diffusion is slower that transport of nutrients by circulatory systems.
Pseudeocoelomates have a body cavity partly lined with mesoderm, such as found in roundworms.
How is pseudocoelom different from a coelom?
Pseudo-fluid filled body cavity partly lined with mesoderm
Coelom-fluid filled body cavity completely surrounded by mesoderm
KNOW FIG pg 683