Man Bits!

Well, I'm pretty sure that Mortiis is a he.

When he was up the side of the tank, I got a decent look at his underside. The pectine's are quite long, feathery and slightly overhanging his sides and his operculum is very much oval shaped, not pointy/heart shaped which would distinguish a female.

I used a few sites to get a decent guess, you can see an example here.

He's been pretty placid at the moment, nowhere near as jumpy as when I first got him so I might give handling a go at some point.