So it's looking like this is most likely to be p. mucosus. Which means diddly because the hobby and science are both vastly lacking in information on both.
Still creeps me out that I never see him eat. With a mouth like that, I expect gobbling of large objects. The other inhabitants destroy pellets pretty quickly so I just have to wonder if he is a filter feeder in some way, or is just really good at eating little bits of food.