Keep Your Shape by Robert Sheckley

Pid the Pilot slowed the ship almost to a standstill, and peered anxiously at the green planet below.

Even without instruments, there was no mistaking it. Third from its sun, it was the only planet in this system capable of sustaining life. Peacefully it swam beneath its gauze of clouds.

It looked very innocent. And yet, twenty previous Grom expeditions had set out to prepare this planet for invasion—and vanished utterly, without a word.

Pid hesitated only a moment, before starting irrevocably down. There was no point in hovering and worrying. He and his two crewmen were as ready now as they would ever be. Their compact Displacers were stored in body pouches, inactive but ready.

Pid wanted to say something to his crew, but wasn’t sure how to put it.

The crew waited. Ilg the Radioman had sent the final message to the Grom planet. Ger the Detector read sixteen dials at once, and reported, “No sign of alien activity.” His body surfaces flowed carelessly.

Noticing the flow, Pid knew what to say to his crew. Ever since they had left Grom, shape-discipline had been disgustingly lax. The Invasion Chief had warned him; but still, he had to do something about it. It was his duty, since lower castes such as Radiomen and Detectors were notoriously prone to Shapelessness.