system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Do worms travel with a single orientation? Do they have a "belly" side that they usually travel facing down with? Or do they just move without caring about their rotation?
gpt
They have a "belly" (abdominal) and a back (dorsal). They are not symmetrical inside. The neural system is the top side, the digestive system is the bottom side. And they aware of which side is up and down.