Only about .02 inches big (half the size of the tip of a pencil point or ΒΌ the width of a nickel), the tardigrade is a microscopic invertebrate that looks like something out of a science fiction movie. Most closely related to insects and crustaceans, tardigrades have 8 legs but look more like the horizontal version of the Stay-Puft Marshmallow Man than any bug or crab.