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Exploring Planaria: Characteristics and Experiments

Discover the world of planarians—simple invertebrates with fascinating characteristics. Learn about their anatomy, movement, and nervous system. Conduct experiments to explore their sensitivity to touch, gravity, light, and food location.

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Exploring Planaria: Characteristics and Experiments

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  1. Planaria Lab Examining a simple invertebrate

  2. Classification: • Kingdom Animalia • Phylum Platyhelminthes (flat worms) • Characteristics of the flatworm phylum: • Bilateral symmetry, cephalized • Flat, thin, tapered body • Made of epithelial, nerve, and muscle tissue, but have very few organs • Most are internal parasites

  3. 3 Major Classes (within this phylum): • Class: Trematoda • Fluke worms • Parasitic • Liver • Blood

  4. 3 Major Classes (within this phylum): Class: Cestoda • Tapeworms • Intestinal parasites

  5. 3 Major Classes (within this phylum): • Class: Turbellaria • Planarians • Free-living, scavengers • Live in ponds, lakes, moist areas etc. • Harmless; part of the food chain • Hermaphrodites • No blood, few organs • Oxygen diffuses into cells directly from water

  6. The Planarian • Very simple flatworm • Soft-bodied, easily damaged, but… Their simplicity allows them to easily regenerate new parts!

  7. Movement • You will notice than the Planarian can twist, turn, and contract (shorten) its body = MUSCLES • You may also notice your worm “gliding” across the water. This is because they have CILIA on their ventral surface that “sweep” them along.

  8. The Planarian • Nervous system: • Photoreceptors: light-sensitive nerve cells • Chemoreceptors: chemical-sensitive nerve cells (taste and smell) • Mechanoreceptors: touch/pressure-sensitive nerve cells • Thermoreceptors: temperature-sensitive nerve cells

  9. The Planarian • Nervous System • Not very complex • Simple “brain” = GANGLIA • Operate on a basic “self-preservation” response to environmental stimulus • Eyespots • Ladder-shaped nervous system • Longitudinal nerves • Transverse nerves, latitudinal

  10. The Planarian • Digestive System • Single opening (mouth) • Pharynx: feeding tube • Three-part, branched intestine • Needed for nutrient distribution to all cells • Lack blood, no circulation

  11. Your Experiment: • Are they touch sensitive? Which parts (anterior or posterior) seem most sensitive? • Can they sense gravity (up/down)? • Do they sense light? If so, do they prefer dark/light? • Can they locate food? How? Are they hungry?

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