The Escape Orbit by James White (Ace, 1965)

One of my Lifeline Bookfair treasures!

 

STRANDED ON A PLANET OF MONSTERS

When the survivors of his starship were taken prisoner by the insect-creatures against whom Earth had fought a bitter war for nearly a century, Sector Marshal Warren expected to be impounded in a prison camp like those the Earthmen maintained.  But the "Bugs" had a simpler method of dealing with prisoners--they dumped them on an uninhabited planet, without weapons or tools, and left them to fend for themselves against the planet's environment and strange monsters.  A "Bug" spaceship orbited above, guarding them.

Escape was impossible, the "Bugs" told them--but it was absolutely necessary, for reasons Warren couldn't tell even his own men.

The creature on the cover is a "battler", which is.. well, let's go with the author's description:

If it looked like anything at all, Warren thought, it was an elephant—a large, low-slung elephant with six legs and two trunks which were much more than twenty feet long.  Below the point where the trunk joined the massive head a wide, loose mouth gaped open to display three concentric rows of shark-like teeth, and above the trunks its two tiny eyes were almost hidden by protective ridges of bone and muscle.  Between the eyes a flat, triangular horn, razor-edged fore and aft, came to a sharp point, and anything which had been caught by the trunks and was either too large or not quite dead was impaled on the horn while the trunks tore it to pieces of a more manageable size.  Because it had no natural enemies and was too big and awkward to profit from camouflage, its hide was a blotchy horror of black and green and livid yellow.

—Page 64.

Now how is a self-respecting artist supposed to depict that?