Distinguished by tentacles with which it picks up psychic impressions. House of Dragon represents war. Jhereg - small flying poisonous reptile that lives on carrion. Represents subtlety and misdirection. Athyra - owllike bird.
All houses are noble except the teckla.
Presumably the orca is good old Orca Orcinus, the killer whale. The phoenix is my beloved phoenix. Exactly what it looks like is hard to say, partly for the respectable reason that descriptions are varied, and it is impossible to know which one Brust has chosen. Here's a picture, though. Somewhat eaglelike, apparently.