*Note that the author invented this name. There is no name or explanation given for these beasts. Most of what is below is theory.
They are more like scorpions than the rest, with two massive front claws. They have six legs, like the other shellcased, but the claws appear to be useful weapons. These shellcased also have necks, and more distinct heads with the same two eyes.
They travel with the horde, but based on their rarity, it can be hypothesized they are either specialized for fighting or can mate with the queen, much as drones in an ant colony mate with the queen.