I've had a group of five Pajama Cardinal fish in my reef now for about 9 months, I believe. They don't move about much, but at night they seem to be on the prowl. These are nocturnal fish, not unlike Bengaii Cardinalfish (wiki: http://en.wikipedia.org/wiki/Banggai_cardinalfish).
The difference between the males and the females is the shape of the jawline. The males have a dump-truck like jaw, and can carry babies in their mouth until they are ready to release. I've been watching mine for a while, and had a feeling they were carrying. Yesterday, I got the camera out and hoped to get some proof.