Altain, explore an alien zoo ship. They find:
a giant tendrilled shark;
tiny, flying, scaled, glittering reptiles;
tiger-striped, bear-sized, clawed, carnivorous mammals (tiger apes);
red, six-legged, otter-like creatures;
black, faceless, hydrogen-breathing quadrupeds with six ropy arms, two ending in boneless fingers, living under high pressure in triple gravity at seventy below (tentacle centaurs);
snakes living in the same conditions as the tentacle centaurs;
a green, scaled, elephant-sized quadruped with a trunk ending in psuedodactyls (the elephantoid);
large, oxygen-breathing bipeds with sphincters in their necks (gorilloids);
small, helmet-like quadrupeds with tentacles ending in cilia and human-like eyes (helmet beasts);
dark blue, silver-spotted, man-sized, oxygen-breathing caterpillars with two arms and hands, each with no thumbs but six opposable fingers, from a high gravity planet (catterpiggles).
This shows the difficulty of imagining alien animals without comparing them to Terrestrial animals. Superman had an extra-terrestrial zoo in his Fortress of Solitude. As described by Alan Moore, this contained "neonmoths" that shrieked with human voices and sentient puddles that evaporated when overexcited.
This comparison of a Nicholas van Rijn story with a Superman story is not frivolous. Although Superman initiated the new genre of "superheroes," he himself is an sf character who, while flying through space, can encounter interstellar traders like van Rijn or pirates like van Rijn's enemies in this story, the Adderkops.
(How can the Adderkops, having colonized a planet in unknown space a century ago, have increased the number of their warships since then?)