no legs, fins or wings

I write about a little animal that is not welcome in any house. Mostly it can be found in humid rooms. During the day it hides in cracks in the wall or floor. When you see it, then it escapes very fast back in the cracks. It moves without legs, fins or wings. It's difficult to get rid of the little creature with the nice name. Have you ever had the pleasure to meet one in your bathroom?