Maybe the one at the bottom of the page??
http://www.surg.co.za/home/html/qand..._cucumbers.htm

http://www.surg.co.za/home/images/qa...udenfeldii.jpg

Stating to think that it's a cucumber. However I can seem to find what kind it is. Does anybody have a good invert identification data base that they use?

Sea cucumber gets my vote, too.

I think the only real risk is if it dies, or barfs up its internal organ. It could poison your whole tank. I would remove it for that reason alone, but my risk acceptance is pretty low.