The excation are a speculative biology project I've been working on, specifically life adapted to seriously harsh environments.

They are strange; they have an endo and exoskeleton, two vascular systems, one of which has blood that becomes toxic when it reacts with carbon dioxide, they breath oxygen through their ear like structures, exhale ammonia, are environmentally sealed to avoid water loss, and can survive in space because of it, and can change gender when they moult.

All in all, not your standard alien.