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 “self-

preservation” 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?