1. Ch. 27.1

2.  Worms are not just earthworms.  Very diverse group of organisms (long, short, thick, thin, blobs, gliders, etc.)  Body shape is good for ease of movement  Have mouth, sense organs, (some) brains  Can easily respond to stimuli

3.  Phylum PLATYHELMINTHES  About a few millimeters thick  Simplest animals to have 3 embryonic germ layers, bilateral symmetry, cephalization

4.  ACOELOMATES  without a fluid filled body cavity  Has an endoderm only  Have a ‘head’

5.  Use diffusion for respiration and circulation  Some have organ systems for digestion, excretion, response, and reproduction

6.  Parasitic flatworms evolved from free-living ancestors  Usually simpler structure compared to their free-living relatives

7.  Carnivores or scavengers  Gastrovascular cavities (two directional; food and waste go in and out the same hole  PHARYNX – muscular tube near mouth  Parasitic worms feed on blood, tissues, pieces of cells within the host

8.  Diffusion to transport oxygen and nutrients  Some have FLAME CELLS that help filter and remove excess water from the body (similar to our kidneys)

9.  Head encloses GANGLIA  group of nerve cells  Have EYESPOTS  detect the amount of light in the environment

10.  Cilia for gliding  Muscle cells to twist and turn for rapid movement

11.  Most free-living are HERMAPHRODITES  both sets of reproductive organs  Sexual reproduction, two worms join in a pair  Asexual reproduction is FISSION (splits in two).

12.  Turbellarians: Free living, live in water  Bottom dwellers

13.  Flukes: Parasitic  Infect internal organs of host  (online activity)

14.  Tapeworms: long, flat, parasites  Live in intestines of host