At first glance, a Skydrifter, floating passively through the upper troposphere, might be mistaken for a large cloud. But this is no cloud. It is actually a colonial organism, like a Terran siphonophore. Each part of the colony is an independent living being called a subunit.

Different subunits perform different roles in the colony. Fin-shaped subunits steer the Skydrifter through the air currents. Support subunits, filled with hydrogen gas, help keep the colony aloft. The colony even has subunits that act like sensory organs: a melon-shaped subunit uses sonar to help the colony navigate, while a net-shaped subunit works like a giant mouth, using suspension feeding to catch aerial microbes, an important source of food for the colony. The subunits have polar membranes on their surfaces, and since polar surfaces are attracted to other polar surfaces (per the principles of intermolecular forces) they remain attached. A network of chemical signals acts like a sort of "nervous system" for the colony, by coordinating the actions of each subunit.

The lifting capacity of hydrogen gas is small, even in an atmosphere with three times the density of Terra's. So the Skydrifter has to be extremely large to remain aloft. In fact, it is over a kilometer long, dwarfing even the biggest of Terran creatures, the Blue Whale. Despite its immense size, the colony is incredibly lightweight, weighing only just over a ton. This is mainly because the subunits are made out of a thin, styrofoam-like material. If it were any heavier, it would sink rapidly.

No Terran organisms have ever evolved in this manner. It may be that Terra's atmosphere is too thin to support floating gasbag creatures, and the lack of food sources in the atmosphere precludes any impetus for a Terran creature to exploit such aerial niches. Melidora's atmosphere, however, is thick and laden with a rich mixture of aerial microbes, so there is plenty of food for giant floating creatures.