weird jelly creature that splits brown stuff

Ok, so here it is. I've been seeing movements every since i've gotten this live Fijiji rock.
Today i've saw it, it is like a head with a mounth, has some tentacles coming from the month, eye on the sides. When a fish came around it has splitted some brown stuff 3 times and was hiding fast.
What could be?
Snail without a shell?
Don't say it could be a Sepia?
I've tried to pictured the best i could;

 

i think it is a snail without shell

it moves like one;

 

stomatella snail, there good to have and breed fast in aquarium which is good cause there good tank cleaners.

 

Yep, I agree. Stomatella.

 

I just discovered one of these in my tank a couple of weeks ago. They are kinda weird. Looks like a curved finger nail.