>>Their legs appear to be cylindrical stumps... or at least, their feet don't stick out as much as you'd think they would... kinda like hooves I guess?
>>Big eyes
>>The option to have pointed ears and a hairy tail.d
>>In profile you can see that they have "anime noses" rather than noses like humans- not so much noses as some sort of muzzle, actually.
>>The Trojan Knights are corrupted/undead Spiral Knights and have big Chess Knight heads
>>The Spiral Order's coat of arms has a chess knight with a spiral design incorporated into it
>>Knights are commonly associated with horses.
>>A certain internet fandom has infiltrated this game since the launch date.
Conclusion: They are anthropomorphic equines. One of the most common ways I've seen people draw anthro horses (in general!) is by making them have horse legs/hooves, horse-like head, mane, ears, and tail but have human arms/torso structure.
Or maybe their just a species beyond our grasp of understanding. They run on energy so they could also be at least part machine. Either that or its the armor and weapons that use the energy. I kind of like the mystery for this game. They are human enough to relate with but they are still a mystery. ^^