I bought a yellow sea cucumber a while back it was cheap and his little fan was sticking out so I tacked him on the bill. I just looked in the tank and bam hes cut in half so crazy I thought he was hurt but hes reproducing all by him self
This is totally normal behavior. They pinch in in the middle until they split and then the head end grows a new butt and the butt end grows a new head.
I have one of those too... It has split three times since I've gotten it. It twists in the middle and then the end half grows a mouth after a few days.