HA, no idea..

[artur]

I know pictures are not good but please try... Looks little like snail.. really little house, but can stretch like 3" jumping from rock to rock . During this evolution he was sitting on his end. What is it?

 

[Msmith88]

It looks to me like some type of sea hare. Hard to tell from the pics but a very common live rock hitchhiker.

 

[mr_X]

looks like a stomatella snail to me, but they don't get 3" long.

 

[artur]

When he tried to go from one rock to another he really stretch himself maybe not 3 but 2" for sure.

 

[mr_X]

Google stomatella snail images, and see if it looks similar. They come in many colors.

 

[Starchar]

I agree with Mr. X looks like the stomatella that I have in my tank. They can move really fast for snails too, quite surprising.