Introduction to Platyhelminthes Biology 11 Mrs. Trevelyan

Platyhelminthes 1. PRESCRIBED LEARNING OUTCOMES and VOCABULARY 2. VIDEOS: None  3. TEXTBOOK PGS Section 26.3 pgs 706-710

Overview…

Examples of Members:

Marine Flatworms are Beautiful! Video: Marine Flatworm Swimming http://www.youtube.com/watch?v=zCH37KI_R_E

Three Classes of Flatworms 1. Turbellaria: Free-living flatworms, mostly predators, living in water or moist environments 2. Trematoda: Flukes, all are parasitic and have complex life cycles 2. Cestoda: Tapeworms, all are parasitic and have complex life cycles

1. Unifying Characteristics Bilateral symmetry, no segmentation First to have 3 germ layers! Outer layer (epidermis) is soft and ciliated (has tiny hairs) or covered with a cuticle Parasitic species have a mouth with an external sucker or hook for attachment to a host Digestive system is incomplete with only one opening Muscle layer is well developed (can swim) No skeleton, circulatory or respiratory systems Hermaphroditic, use internal fertilization

2. Structure Cephalisation has occurred (have a head with a concentration of nerve cells) Has 3 cell layers (ectoderm , mesoderm and endoderm) with specialized cells and tissues Development of more complex tissues and organs (e.g. Pharynx, eyespot, muscle layers etc)

2. Structure Some freshwater species have primitive eyespots and can detect the presence of light E.g. Planarians This eyespot is called an OCELLI and is NOT a true eye

3. Digestion One opening (“mouth” with a gastrovascular cavity that is often highly branched throughout the body) Free-living are carnivores or scavangers- pharynx comes out of mouth and “vacuums” up food, also “spits out” solid waste Parasitic flatworms anchor themselves to their host and live off of host tissue/blood Video: Planarian eating http://www.youtube.com/watch?v=w0QzSYQGsnA

Digestion- some are PARASITIC Tapeworm in an intestine Most do not have a complete digestive system because they absorb digested material directly

4. Respiration/Excretion No Respiratory organs Exchange gases by diffusion (hence small, flat shape) EXCRETION Solid wastes exit the body through the “mouth” Gas wastes exit the body through diffusion Freshwater flatworms have FLAME CELLS that excrete excess water from the body

5. Nervous System More advanced than cnidarians Have cephalization and cerebral ganglia (brain-like structure) Nerve cords are organized like a ladder (no netting)

6. Reproduction Flatworms are hermaphroditic (both male and female) Can reproduce aseuxally or sexually ASEXUAL REPRODUCTION: Free-living freshwater flatworms can do this by: Fission- organism splits in two Regeneration- a single part can grow into a new worm

6. Reproduction SEXUAL REPRODUCTION Freshwater free-living flatworms use internal fertizilation Flatworms “join up” in pairs to reproduce sexually. One delivers sperm, one receives sperm. Eggs are laid and hatch in a few weeks Video: Marine Flatworms Penis Fencing: http://www.youtube.com/watch?v=wn3xluIRh1Y

6. Reproduction Parasitic flatworms have a much more complex life cycle, often with more than one host (e.g. infects snails and humans) See and know figure 26.18 on page 710

7. Additional Interesting Facts flatworms sometimes growing to lengths of 40 feet Penis fencing- nuff said