What is it?

[BlueCs]

It came in with live rock almost too small to see. Now it is at least 2 inches long and 1/2 inch in diameter. It moves around on rare occasions. One end with tentacles is for eating, the other end for moving around. I do not know what it eats, but it continues to grow. The photo is over a year old.

 

[MartinE]

Looks and sounds a bit like a sea cucumber (Holothuroidea), try here for more info:

http://www.wetwebmedia.com/seacukes.htm

 

[BlueCs]

Thanks MartinE. It seem that you are right. It has been an interesting resident for 3-4 years, and now more welcome as a cucumber.