Large predatory animals native to Trill, able to blend invisibly into their surroundings, which Burnham and Book encounter while being tested in the episode Jinaal.
Itronoks are big, aggressive creatures found in the wild canyon country of Trill. They can camouflage themselves so well as to seem cloaked, and they defend their nesting grounds fiercely.
They appear in the fifth-season Discovery episode Jinaal. The consciousness of the long-dead Trill scientist Jinaal Bix, temporarily housed in Hugh Culber's body, leads Michael Burnham and Cleveland Booker into the canyons where he hid the next clue to the Progenitors' technology. He neglects to mention the itronoks nesting there.
Attacked and outmatched, Burnham and Book stop fighting when they realise the animals are protecting their eggs, and Book uses his empathic gift to show they mean no harm. That restraint is the quality Jinaal was testing.