I'm not sure to make sea cucumbers but the three I have that survived the trip from TBS laid on the sand and hardly move for nine days! I know they aren't dead ... when one dies it is hard to misinterpret. So, after nine days, the biggest cuke of the lot finally moved last night ... straight to the top/rear of the tank to wedge himself behind a powerhead and has sat there ever since.
Maybe he just likes a jacuzzi ...
Maybe he just likes a jacuzzi ...