I got it in some live rock. I am not sure about this specific one but they have been in my tank for about 7 years. They also split pretty often.
I just gave a bunch away and I can only confirm one in my tank. If you are interested I will let you know when I start to see more pop up and you can have one.
I brought two tiger tail cucumbers from Cantadora Island this is a small island on the Pacific coast of Panama. They both from time to time stretch up to 11-12 in. Have not noticed them splitting or multiplying but they do a great job cleaning sand.