FLATWORMS, ROUNDWORMS, & ROTIFERS

Chapter 34

PHYLUM PLATYHELMINTHES

Section 34.1

General Structure:

3 germ layers – ectoderm, mesoderm, and endoderm acoelomates

Bilateral symmetry Anterior and posterior ends

Dorsal and ventral surfaces only Flat body plan Flatworms!

General Functions:

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

Classification:

Four Classes:1. Turbellaria - non-parasitic

2. Trematoda- parasitic3. Monogenea - parasitic

4. Cestoda –parasitic

1. Class Turbellaria: 4,500 species Mostly marine Swim in wavelike

motion Glide over solid

surfaces on layer of mucus

Example: Planarian Dugesia freshwater

Video

Planarian Body Plan:

Planarian Organ Systems:Digestive System: Scavengers & predators

Decaying plants & animal matter Prey on smaller organism

Pharynx – throat that extends to the middle of body video

Planarian Organ Systems:Excretory System: Flame Cells – enclosed tufts of cilia that draw

excess water together and excretes it through pores video

Planarian Organ Systems: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

Planarian Organ Systems:Reproductive System: Sexual:

Hermaphrodites Eggs laid in protective capsule

Hatch in 2-3 weeks Asexual:

Regeneration video

Video