Mermaid people who live in the sea of ice. They have intermingled with humans creating mixed race people of the "merlines" such as Atlanta who have gillslits and can breathe underwater, but walk on legs.
But beer? Never. For the females of Heaven and Hell fear beer for its calories. But those of the Merlines fear it not. The metabolism of the Mer runs hot, and so too does the metabolism of all those born to the sealines. The inheritors of the sea genes can trough down their food with an appetite a pig would envy, yet stay as slender as the praying mantis.
Atlanta's elegance of figure was matched by no elegance of abstinence. She sharked down her food with the best of them, quaffed her beer, and seldom suffered ill effects from appetite. Not only was she descended from the Mer, but she was also a child of the House Jubiladilia, and the Jubiladilias were notorious for having strong stomachs and heads to match. Atlanta did not easily get drunk, unless she dared a draught of lightwine. Beer could scarcely touch her. [WoH Ch9]
Atlanta's lineage has seen humans mate with the Mer. This makes her of the Merlines - or, as such descent is commonly phrased, of the sealines. Since the woman is thus descended, to undress her would be to discover subtle lines of latency marking the potential gill-gaping of her flesh. At need, her floating ribs can part to feed the sea to her waterlung, and thus to let her breathe beneath water.
Ancestry and ability are mutually marked by her milksilver skin, the sure and surest sign of the sealines. [WoH Ch1]
But there was little Heineman could tell. The Vasakatari, the islands of the Mer, lay in the Sea of Ice, south of the Yontil Yantil. Few people ventured to those regions, for several reasons. For a start, the activity of the metapsychic faultline was alarmingly strong in those southern regions, disconcerting even to Chalakanesians who had a lifetime's familiarity with metapsychic effects. Furthermore, the Sea of Ice was stormy, beset by bad mechanical storms (as ordinary storms are termed in Chalakanesia, to distinguish them from metapsychic storms). Few mariners cared to hazard those southern regions. [NoP Ch6]
One tooth was loose, almost ready to be shed, its replacement having grown to full size behind it. Atlanta pulled it out with a small jerk. There was a brief pang of pain, then nothing. She reached out and let the tooth fall into Gorkindachina's glass of wine. A slight thread of blood unwound from the tooth as it wavered down through the wine, grounding noiselessly at the bottom of the glass.
'You forget,' said Atlanta. 'The Mer don't need dentists.'
Gorkindachina said nothing, but looked at the tooth in his wineglass. How very like a shark! [WoH Ch14]
The floating ribs of a human skeleton are made of staunch bone unyielding, bone as tough as that of skull or pelvis. But those born to the sealines have floating ribs like those of the purebred Mer, floating ribs fashioned from a cartilage like that of the nose. Such cartilage is strong, yet flexible, and accommodates itself to the underwater exertions which allow the Mer and their earth-walking descendants to gill water.
Here 'gill' is a word of vulgar extraction, a word which science shuns, holding that the water-breathing of the Mer has nothing in common with that of a fish. Technically, science is right. The Mer do not breathe water with the gills of a fish. Instead, each of the Mer has a water-lung centered beneath the naval, and it is this organ which feeds on the water admitted between the ribs. Scholars usually characterize this extra lung as an adapted womb (though all the Mer, regardless of sex, possess just such an organ) and claim that it wins oxygen from seawater by a process analogous to that whereby a baby wins air from its mother's blood.
Shall we argue this out in detail? [WoH Ch1]