D&D Monsters: Rust Monsters

The rust monster is, like the bulette, a creature inspired by a cheap plastic toy bought in Hong Kong. The original toy apparently looked like a lobster with a propeller for a tail, perhaps to represent some weird aquatic kaiju. Gygax later admitted that he'd initially been stumped as to what special attack to give such a ridiculous-looking creature, but, of course, he eventually came up with something that made it a particularly memorable and unique monster. One that is essentially a walking hazard, an annoyance that's completely harmless by the usual standards of the game but nonetheless very much to be feared. 

Albeit, like displacer beasts and piercers, one whose name is just a rather bland description of what it does. 

D&D Monsters: Remorhaz(es)

The remorhaz is another creature original to D&D, and one of the few such that is honoured with a proper name rather than a descriptive term. It's one of the more powerful creatures in the 1st edition that are described as simply animals, rather than intelligent beings. This is largely because it's so difficult to hurt, although it also has a bite that does more damage than that of most dragons. In later editions, it's toned down, although it remains quite fearsome.

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1E

As originally depicted in the 1E Monster Manual, the remorhaz has a snake-like body, with a thick leathery hide that's harder to penetrate than plate steel. The upper surface of the body is covered with an irregular array of white protuberances, which apparently shed excess heat from the intestines. The lower surface has a series of wide flat scales, which also resemble those seen on many snakes, reinforcing the resemblance. The key difference, of course, is that the remorhaz also has a huge number of legs. These are multi-jointed and covered with an exoskeleton; the segments within the leg are all of similar size, suggesting the relatively simple structure of a centipede's legs rather than those of a spider or insect.