Phylum Platyhelminthes Name? From 2 Greek words: ‘platy’ meaning flat and ‘helminth’ meaning worm Characteristics: Have tissues and internal organs Have 3 embryonic germ layers – endoderm, mesoderm and ectoderm Bilateral symmetry Cephalization Acoelomates – No body cavity persent

3 Main Groups or Classes: Turbellaria – Free living, most live in marine or Fresh water. Example: Planaria (Fresh water)

Marine dwelling:

Some live on the forest floor:

2. Class Trematoda (Flukes): Parasitic flatworms often living in the host’s internal organs. Some are ectoparasites on the host’s skin, mouth, gills, etc.

Liver fluke in deer

3. Class: Cestoda Tapeworms – Long, flat parasitic worms adapted to life inside the intestines of their hosts.

Characteristics: Have tissues and internal organs Have 3 embryonic germ layers – endoderm, mesoderm and ectoderm Bilateral symmetry Cephalization Acoelomates – No body cavity persent

Specialized structures: Free living flatworms: Ganglia (groups of nerve cells) that control a nervous system – primitive ‘brain’. Also have eyespots to detect light with

Free living flatworms have mouth with a pharynx that pumps food into the digestive cavity.

Free living flatworms have muscle cells to aid in movement Some flatworms have flame cells that help them remove excess water and also wastes like ammonia and urea from the body. (Help with excretion)

Parasitic worms such as tapeworm: Head (scolex) contains several hooks or suckers that are used to attach to the intestinal wall of the host

Mode of nutrition: Free living flatworms: Predators or scavengers – eat molluscs, protozoans, crustaceans, some live with algae that provide them with carbohydrates. Use pharynx to pump in food into the mouth. Have a digestive cavity or gut. Parasitic flatworms: Feed on blood, tissue or pieces of cells within the host’s body. Tapeworms have no digestive cavity – simply absorb nutrients that Are already in the host’s intestines.

Movement: Free-living: Use cilia and muscle cells to glide, twist and turn. Reproduction: Free living: Hermaphrodites and reproduce sexually. Sperm are delivered between 2 flatworms. Eggs are laid and hatch in a few weeks. Also reproduce asexually through fission.

Parasitic flatworms: They have complicated life cycles that can involve both sexual and asexual reproduction. http://science.jburroughs.org/mbahe/BioA/starranimations/chapter23/videos_animations/tapeworm.html