In case you missed it, the starting point was the realism of aliens in fiction, whether wargames, cinema or literature. The whole thing was set off by our new friend, the squid worm. The question was how the preoccupation of the moment might mean we make the alien less realistic.
Let's start with a biggie, Dune by Frank Herbert, and the sandworms. Look away now if you're squeamish - the film version is definitely not for you.
I was grinning by the final shot. Remember, it is a David Lynch film...
If you haven't read the book, I recommend it. It's a modern classic and for good reason, not least perceptive writing and immense scope. (If you're a young man, try to keep a sense of proportion.)
Getting back to zeitgeist, the big issue of the time was ecology and the book highlights the interrelatedness of life at every turn. The sandworms are vital to Fremen culture and in fact interstellar civilisation, but the water we need kills them. They get a complex life cycle which we rely on. As a fictional device they seem to be telling us we ignore the natural order at our peril.
As for the physical, they're massive and powerful, but subtle with it. They sense shifting sands and strike from out of sight. (They're faster and more dangerous than the clip suggests - in the same film, the worm in the harvester scene leaps clear of the sand.)
All in all, the sandworms are masters of their world and ours, and represent the destructive potential of even a small miscalculation or lack of knowledge. It doesn't matter much who makes it - an unsuspecting wanderer in the deep desert or a society changing a world to suit themselves. We're all in trouble.
I'd guess in this case the mood sneaking in was more design than accident. If you're an intelligent guy writing an SF novel three years after Silent Spring, you might well have a sense of wonder, a sense of pride in a lesson learned or just a sense of mission. (And the last is reflected in the plot after all...) The sandworms would then be a defence of mother nature's honour, some forgivable showing off or an educational tool.
The point is that there is a point. The creature is a product in part of the preoccupation of the author and his society at the time. Science and imagination must coexist also with this driving force. The lifeform is less likely to be a realistic vision for the compromise.
So what does this mean for the creature's shape? A happy coincidence? A whole other post I think and I'll leave it for someone else...
The sandworm of Dune then. The astrobiological organism for its time?
Update: This was re-posted here about three months later, beginning a new discussion.