ch. 24, section 2

what marks the branching points on the evolutionary tree?

animal’s anatomical features

relationships on the evolution tree are inferred by what?

studies of similarities in embryological development and shared anatomic features

what was the first major change in body plan?

the development of tissues

what is symmetry:

the balance or similarity of an organism’s structure and the next branching point after tissues

what are the different types of symmetry?

asymmetry, radial symmetry, and bilateral symmetry

asymmetry:

irregular shape, no symmetry or balance (example: sponge)

radial symmetry:

can be divided along any plane, through a central axis (example: jellyfish)

bilateral symmetry:

• can be divided into mirror-image halves along only one plane (example: bird)

• animals with bilateral symmetry also have an anterior and posterior end

what is cephalization?

a tendency to concentrate nervous tissue and sensory organs at the anterior end of the animal

anterior:

head

posterior:

tail

ventral:

belly side

dorsal:

backside

animals with bilateral symmetry have a gut, which is:

either a sac inside the body or a tube that runs through the body, where food is digested

how many openings does a sac-like gut have?

one

how many openings does a tube-like gut have?

two

name the types of body cavities:

1. coelomates

2. pseudocoelomates

3. acoelomates

coelomates:

mesoderm-lined, fluid-filled cavity between gut and outside wall (example: mollusks)

pseudocoelomates:

(false cavity) one partially-lined, fluid-filled body develops between mesoderm and endoderm (example: roundworms)

acoelomates:

no coelom, have solid bodies without fluid-filled body, and no circulatory system (example: sponges)

protosomes:

coelomate animals that develop mouths from the first opening in the gastrulas and the anus from the second opening

deuterostomes:

coelomate animals that develops the anus from the first opening in the gastrulas and mouths from the second opening

segmentation:

evolutionary development which allows segmented animals to be “put together”

animals advantages of segmentation:

• can survive damage to one segment because the other segments can carry out the functions of the damaged

• movement is more effective