I asked Ron Shimek about it, and he stated:
Hi Ralph, Yup, it looks like Cryptoplax</em> to me. Don't worry about trying to find "perfect" matches to any given image. These animals are individuals and the coloration can vary a lot from animal to animal. By the by, it is a small one, they reach lengths that can exceed 10 cm (4 inches).
and my response:
Thanks!
at this point he has been pretty "harmless", but would you suggest that I have him removed so he doesn't rasp my overflow, silicone, or enter my pumps?
Ralph
and his:
Hi Ralph,
I really see no reason to remove it. If it seems to become a problem, it can be removed then, but odds are great that it will not do any harm whatsoever.
Cheers, Ron