can anyone help me what is this white snail type thing

hi everyone,



I am new to this so hoping that someone can help me, i was looking at my marine tank last nite and seen this little creature on my rock.



It is white and looks abit like a snail but down its back it has what looks like a spilt and a wiggly pattern on it.



It wouldn't let me upload pics :(, so mayb no one will know what it is :(



I hope someone can help tho :)