The skirt itself, when inflated, was probably a delicate sense organ. Slight updrafts would indicate sources of heat on the ground. The cilia seemed to have chemical sensors, like olfactory receptors, that would help the spider differentiate between a warm rock and a potential meal.

The digestive system was relatively simple, the mouth used for both ingestion and excretion (when Seven learned that, she washed her hair again). More than half the volume of the ropy tentacles was bladder rather than muscle, and there was a sphincter under each tentacle claw. The bladders were full of sulfurous-smelling water that evidently served as ballast.

The next day, an exploration party less than two kilometers from the camp worked their way over a ridge into a valley of rank yellow and orange vegetation, and smelled something that reminded them of the floating spider. Weapons drawn, they crept up on a bubbling swamp.

One of the creatures was splayed across the water, its tentacles moored to various anchors. It was sagging, partially inflated. It had stationed itself over a spot where a steady line of bubbles broke the surface.

No one in the party recalls anyone making a sound, but the animal sensed them somehow, perhaps by smell, and its reaction was swift. The tentacles let go of their moorings and sprayed water in twelve directions as the gasbag snapped shut. The creature rose fast, like something falling into the sky. People fired at it, but it was a difficult target, bobbing in crosscurrents, and in a few seconds it was just an iridescent dot sailing away. Dozens of other small bubble creatures flew away in reaction.

The exploration party people spread out around the perimeter of the swamp and surveyed it. It was a circle about twenty meters in diameter, with steep banks, like a crater or sinkhole. One person volunteered to wade out, but quickly sank up to his knees in muck; it took several people, pulling on a rope tied under his arms, to extract him.

Throwing the rope out with a light weight attached, sounding, showed that the pond was nowhere more than a couple of meters deep. It had probably filled up with decaying vegetable matter. (One of the team, a biologist, noted that unless this was a transient condition, there had to be Something Down There keeping the level constant. The leader asked with a straight face whether anyone would care to swim across and see if anything happened.)

One of the helium outlets was close enough to the shore for them to fill a sample jar without wading. They collected four samples of small gasbag organisms and counted thirty-nine others scattered across the surface. All but three of them had green tendrils inside, though it would have been premature to therefore call them plants. There are unicellular Earth animals like the euglena that can photosynthesize.