The planaria cannot swim through the water. It has many 'cilia' or hair like fingers. These are mostly on its underside. It also has many glands on its underside that give off a mucous or slime. The cilia find traction or hold along a trail of slime.
Planaria can only move again a solid surface like a stone, stick or leaf.
They also manage to move along the underside of the surface film of the pond using their slime trail. Planaria glide slowly over a surface with their head bending from side to side to test where they are going. Their bodies are very agile with no hard parts. They can bend in any direction, flatten very thin or pull their bodies up shorter to escape enemies. Planaria reproduce or have young sexually much like earthworms.