Well, I assume that's what he is. His cup at petco was labeled "Male Doubletail", but he's transparent white, and definitely halfmoon when he flares. I picked him up last month, and haven't gotten any newer pictures of him since (because my camera really sucks, and I have no idea where the charger for it is, yikes), and the transparency never went away. He's very, very small, too. Less than 2 inches.
But here he is
! His name's Jarvis. c:
(And before anyone asks, he's not in that little tank anymore. I got a new 3gal for Christmas, and that's his new home. c: )