When an Omo lays it's eggs (usually down some willing or unwilling victim's throat) the egg latches onto the stomach lining or upper intestinal wall and remains there for up to a week. Once it hatches, an Omopole is born, and will swim up and down the host's digestive tract for the next year or so, until it begins to develop arms and legs, and decides to leave through one orifice or the other. Generally the host suffers no long term harm, though they may need to eat significantly more than average to maintain healthy weight.
Art by LivingTrashSteiner