The sleeping urhook is an ankylonychoid (literally meaning hook-clawed), a desert-dwelling offshoot of it's swamp-dwelling ancestor. It has almost fully adapted to life on land, losing it's heavy shell and adapting it's fins and tail into three pairs of strong fin-feet. It's skin has become thicker and less porous, so that it can hold in water better than it's ancestor, which can make the difference between life or death in the dry reaches of the desert. It's back has also turned into a fat storage region, and much of the food that the urhook manages to get is stored here as fat, to be used as nutrition later on.
The sleeping urhook's name is well earned, for it spends much of it's life in biostasis, incubating in a thick mucus sac far under the sands. It will only be active for two months of the entire year, during which it breeds and eats, functioning as a surprisingly efficient ambush predator. The difference between breeding and eating for a sleeping urhook is very small - both involve burying themselves under a thin layer of sand, and waiting for either unwary prey or an unwary urhook of the opposite sex to pass by. If prey passes by, the hook is swung up and injects or impales the prey with a liquefying toxin. If another urhook passes by, the ambush urhook springs out of the sand and pins the passing urhook, than releases either a glob of eggs or a puddle of sperm over the other urhook. The reproductive gametes get stuck in the thin layer of mucus that covers all sleeping urhooks, and remain there until the eggs are fertilized by the opposite gamete, which is secreted through the skin. The eggs incubate in the thick layer of mucus that is created by all hibernating urhooks, and hatch the next time the parent emerges out from the sand.