Hello, It does look like a larvae of some kind. I have never had one in my tank, however, a friend of mine got something simmilar in his tank a few years back. It showed up in his tank after feeding blood worms. We are still, even three years later, not 100% sure of what it was or how it got there but we believe it came in with the blood worms.
My advice take it out immediately, and if you have feed any different foods (ie different brand, blood worms etc) recently throw away that food.
Good Luck.