Thanks for the link, Quinn
Read the article, then did a little more research on medusa worms, which is what my "friend" might be. States the animal may be toxic and may be roaming the tank during daylight because it is: a) starving, b) not worried about predators. Some medusas have a commensal relationship with specific sponges and without them, slowly starve
Here's Rob Toonen's page on medusa worms:
http://www.reefs.org/library/article/r_toonen7.html
If I see the worm again, I will contact you, if you are still interested. My 42 gal is probably not big enough for it, though there is detritus all over the place if it is a species interested in detritus. Am a little concerned it may be toxic and starving. Sure don't want this possibly toxic thing to die in my tank. Had that happen in my 180 a few years back and 3/4 of my fish were wiped out overnight
Have sent the photo to Rob Toonen for possible ID. Will let you all know what he says.