Friend or Foe?

[justinl]

some kind of sea cucumber (hard to say what species). Judging by the feeding appendages (head mop thingies), this one is a surface deposit feeder... ie: poop eater. ie: good as a part of your CUC.

Despite that however, most cukes are toxic to a degree and if it dies in a nano, it has the potential to cause some trouble. In a bigger tank it shouldnt be any worry. If its in a nano and has cohabitants that might cause it to go toxic, you might want to remove it. It isn't too difficult to keep most cukes happy though; decent water quality and low stress. Your call in the end.