Wikipedia tells me that Mephisto and Mephistopheles are one and the same. Both refer to the demon whose picture is at left. Sometimes Mephisto is seen as the devil himself. The term comes from German folklore and was first seen in print as the demon in the Faust legend. The name is familiar to me in part from Faust but more because of the movie, "The Mephisto Waltz (which I wrote about in this post).
So: a devil, a demon. But why name the worm after this creature? I wondered if it was because the mythical hell lies deep beneath the Earth so I googled my way to this reference:
". . . Halicephalobus mephisto, an entirely new species, with the mephisto portion given in reference to its residence in the underworld"
Mystery solved and the meme of mephisto is passed on to another generation . . . well, to science and work geeks, anyway. Oh, and you.