Chapter 34
Section 34.1

3 germ layers – ectoderm, mesoderm, and
endoderm


Bilateral symmetry


acoelomates
Anterior and posterior ends
Dorsal and ventral surfaces only


Flat body plan
Flatworms!

Exchange oxygen and carbon dioxide directly
with the environment to cells by diffusion



No circulatory system or respiratory system needed
Only one opening where food and wastes pass
through!
Cephalization

Four Classes:
1.
Turbellaria - non-parasitic
2.
Trematoda- parasitic
3.
Monogenea - parasitic
4.
Cestoda –parasitic





4,500 species
Mostly marine
Swim in wavelike motion
Glide over solid surfaces
on layer of mucus
Example: Planarian
Dugesia

freshwater
Video
Digestive System:
 Scavengers & predators
 Decaying plants & animal matter
 Prey on smaller organism

Pharynx – throat that extends to the middle of body
 video
Excretory System:
 Flame Cells – enclosed tufts of cilia that draw excess
water together and excretes it through pores
 video
Nervous System:
 Cerebral ganglia: two clusters of
nerve cells at anterior
 “Brain”
 Can learn
 Eyespots: sense direction and
intensity of light

Other senses: touch, water
currents, chemicals
Reproductive System:
 Sexual:


Hermaphrodites
Eggs laid in protective capsule
 Hatch in 2-3 weeks

Asexual:


Regeneration
video
Video