E. Tissues

i. During gastrulation different layers of tissue develop

ii. Ectoderm

a. Outer layer

b. Give rise to the outer covering of animals

c. Hair, reptile scales and feathers

iii. Mesoderm

a. Between the ectoderm and endoderm

b. Forms the muscles and many of the organs

c.* Not found in the radiata (cnidarians and ctenophores) bilateral only

iv. Endoderm

a. Inner layer

b. Gives rise to the digestive tract and associated organs

F. Body cavities

i. Bilateral animals are further divided into 3 different groups based on body cavities

ii. Acoelomates

a. Have a solid body with no cavities between the layers of tissue

b. Flatworms

iii. Pseudocoelomates

a. Have a cavity between the endoderm and mesoderm called pseudocoelom: false cavity

b. Rotifers and roundworms (nematodes… not segmented)

iv. Coelomates

a. Most bilateral animals

b. Have a body cavity: coelom surrounded by the mesoderm

	Created by Shelby Klein over 6 years ago

Animals

Chapter 32