Planaria Lab
Examining a simple invertebrate
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 Major Classes (within this phylum):
• Class: Trematoda
–Fluke worms
• Parasitic
• Liver
• Blood
3 Major Classes (within this phylum):
Class: Cestoda
–Tapeworms
•Intestinal parasites
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
The Planarian
• Very simple flatworm
• Soft-bodied, easily damaged, but…
Their simplicity
allows them to
easily regenerate
new parts!
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.
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
The Planarian
• Nervous System
– Not very complex
– Simple “brain” = GANGLIA
– Operate on a basic “selfpreservation” response to
environmental stimulus
– Eyespots
– Ladder-shaped nervous system
• Longitudinal nerves
• Transverse nerves, latitudinal
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
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?