Sserrinvor

Body

Fourteen feet, ash-grey, gilled as well as lunged, with the six frilled slits along the throat that give them their name and a mouth of hooked teeth in rows. There is no gas anywhere in the body; a light oil fills the places another Sserrin keeps air, so pressure passes straight through them and does nothing, and the same arrangement means that rising expands and tears them. Their eyes are enormous, lidless and useless in any light at all, and above a hundred fathoms they are simply in agony and cannot be argued into staying.

That same light oil is why a Sserrinvor body is a fortune: their oil is the best there is, almost never sold, and the lines know it, which is why no Sserrinvor body ever comes up.

Faith

They are the clergy, and their doctrine is the Descent taken to its end: that the god is not below the deep but is the deep itself, and that the songs are him talking in his sleep. They go deeper than any other strain and come back up singing, which is the whole of the species's worship, since there is no temple and no altar, only a depth.

The deep carries sound, and the Sserrinvor bring up, in the shift, songs they say they did not compose: the songs of the drowned realms, the places the sea took, sung in tunes and words no living people uses. They sing whole liturgies of a faith nobody recognises, lists of names, harbour registers, and one long lament that every Sserrinvor knows identically and no two of them can explain.

They also sing back the names of the let-go, which is the part that matters to the lines, since a family that hears its own dead in a song it never taught anybody stops asking where the songs come from. Two of the harbour registers have been checked against every port record on the Surface Realm and match nothing that has ever existed above water. The lines treat these songs as scripture and the Sserrinvor themselves treat them as testimony. Whether the drowned realms are the sunken cities of the god war, the works of some people the Alverians culled, or something older and still down there singing, the Sserrinvor will not say, and the reasonable reading of that is that they know.