Chapter 34

Section 34.1

 3 germ layers – ectoderm, mesoderm, and endoderm  acoelomates  Bilateral symmetry  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 video

Excretory System:  Flame Cells – enclosed tufts of cilia that draw excess water together and excretes it through pores  video 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 Video