"Their glassy blackness recalls Mt Nomad, the predatory terrain feature which haunts the blackness of Void's Approach. What is their connection?"
One of the Unterzee's most ferocious Zee-beasts, the creature known as Mt Nomad is a gigantic, purple mountain floating in the most northerly reaches of the Zee, near the mysterious Avid Horizon. Her mother is definitely the Zee-god Stone; her father is the Thief-of-Faces, the first Snuffer. It is rumored that the Fathomking is her uncle (on her father's side), as he unleashes Salt's Curse on those who bring her heart as a trophy.
Mt Nomad may also be connected to the Lifebergs that drift near her in the Void's Approach. It is unknown what these creatures are or what connection they have to the far more fearsome Nomad, but they share some connection to the Void beyond. Perhaps they all share a father, or perhaps she is their mother, but of course we cannot ask either party for the truth.