sea cucumber?

so i got some more live rock the other day and i noticed this little critter wedged in a crevice, i put him in front of the tank to watch what it was. after about 4 days it just lay in the same spot i thougt it may be a shell stuck, or piece of the rock. well today after i fed my fish i looked at it and it had 8 long filter tentacles in the current catching bits of brine/ mysis and pulling them in. pic below is kinda fuzzy, ill try for a better one tomarrow if it opens. its light and dark brown body and has 8 tan colored tentacles with red dots on each. can any one tell me waht kind of cucumber this is, and is it bad? its only about 1 inch body and 1 inch across the tentacles. very cool to watch. should i keep it? i hope so.
i added anothe pic. will this thing spill its guts and poision my fish?

 

here is another pic. cant get much better for some reason that is the only spot in my tank my camera wont focus on. annoying!!
i just dont want it to spill its guts in my tank and posion my fish. anyone have any advice on this?

 

really...in the pics you can't tell it is too blurry.....anything missing from your tank? can you see a round cylindrical body? does it poo out sand?

 

yea u definently need some new pics of it cuz it looks all distorted.

 

Yep thats one

HI,
That sure looks like the eating end of one,
I had one in the sump and he bumped into a heater or crab or something and slimed the entire sump,skimmer, and main tanks filters, it was the most rigid material I ve seen in a while. looked like strands old elmers glue that became some type of epoxy super resign... geeze what a mess I never found the little things i guess he went to turd heaven...
They are very good filter feeders , but may get ticked off and slime a tank. some say the slime is alittle toxic to some inverts.
doug