Ludus:

Bold and hardy, the Ludus are known as courageous warriors, farmers, and workers of the land. Their bodies are covered in a shell which is rigid but supple as the situation demands in jointed parts of the body such as the fist. They are not, however, strictly invertebrate, having an internal skeleton broadly resembling that of a human. Outwardly, Ludus vary widely, most obviously in that a caste of Ludus from the Frigid Caps and surrounding tundras have stark white shells- the Niveus- while those from the Verdant Plains and beyond are pitch black- the Furvus. Beyond coloration, however, it does not seem that the two castes are at all biologically different.