African flat rock scorpions, and H. troglodytes is the longest scorpion in the world, though most of that length is tail.
Extraordinarily flat, which is the entire adaptation: they live pressed into rock crevices and can wedge into gaps that look impossible. Venom is mild. They are slow, they are calm, and they live a very long time, with reports well past two decades.
They also grow extremely slowly, which matters commercially. Captive breeding is impractical at that rate, so the market is almost entirely wild-caught South African material, with irregular availability. A large specimen is an old animal that took many years to reach that size in the wild, and no amount of money accelerates producing another one.