Still, that brief period of first contact had provided humanity with most of its understanding about the Qax and their dominion. For instance, it had been learned that the Spline vessels employed by the Qax were derived from immense, sea-going creatures with articulated limbs, which had once scoured the depths of some world-girdling ocean. The Spline developed spaceflight, traveled the stars for millennia. Then, perhaps a million years earlier, they had made a strategic decision.
The Spline rebuilt themselves.
They plated over their flesh, hardened their internal organs — and rose from the surface of their planet like mile-wide, studded balloons. They had become living ships, feeding on the thin substance between the stars.
-Timelike Infinity, Ch. 1