The flukes also called flatworms or platyhelminthes have a false body cavity or pseudocoelum which exist as patches between the body wall and the intestine, they do not originated mainly from the mesoderm like the true body cavity.
Fluke is a flat worm that belong to phylum plathelminthes. Flat worms have no body cavity also called aceolamates but they are bilateral symmetrical. They are unsegmented, soft bodied and lack no circulatory and respiratory organs. Their digestive system has only one opening for ingestion and excretion( removal of water material). The cannot process food but nutrients are diffused into their body.
The movement is a called a reflex, which is a sudden muscle movement in response to a stimuli. The reflex you are describing is a reflex known as a plantar reflex, which is present in infants and children but goes away before adulthood (ideally).
