There are no roots. Can you describe the dark spots around the stem. Is the stem firm or mushy. Look into propagation of cactus. I am sure it can be saved, but I am no expert with cactus. I do know you have no roots. Until you learn some answers don't stick it in wet mediums, you are safer to keep it dry than damp. And that is the extent of my knowledge, hope someone here will come and point you in the right direction.
