While his daughter Aurin wears a Trigger Stone around her neck which allows her to control the arachnid Keriag race, Macaan possesses a second, implanted directly in his forehead, which allows him to control both the Keriags in addition to the Jachyra.
Aurin wears a Trigger Stone around her neck that allows her to manage the Keriag spiders, whereas Macaan carries an additional implant on his forehead that lets him control not only the Keriags but also the Jachyra.