The Triscene, though part of the alien reserve forces in the Second Alien War, is actually an Earth creature, harvested from the prehistoric ages when the Alien Colony Ship T'leth crashed landed upon the site that now resides at the bottom of the Gulf of Mexico. They are a breed of Terror Unit that ravages the coastlines and shipping lanes in the late stages of the game.
Triscenes can be described as a hybrid of the Reaper and the Sectopod. It has bright orange skin that can accept a generous amount of damage before dying or falling unconscious, at the same time feeling all warm and fuzzy inside knowing that the Aquanauts wasted about half of their guns' ammo taking it down. It has two means of attack, which is where the Reap-Sect Hybrid part comes in. Like the Reaper, it can rend its enemies(whether they be a civilian or an unlucky Aquanaut) with razor-sharp alloyed teeth. And like the Sectopod, it can dish out generous amounts of Sonic-based ouch from the twin sonic blasters slung on its back. They also have good reaction time, due to their reaction time. I once had encountered a Triscene on a Port Town Attack that was standing right outside the troop transport sub, and it had whirled around and opened fire JUST WHEN one of my Aquanauts opened the door to enter combat, taking out one of my unarmored fresh recruits(I had suffered systematic losses earlier) in one shot. Next turn, it let fly another sonic blast and killed one of my troops in Ion Armor. So yeah, they have good reaction time and dead-center accuracy, so make sure you take it out before it notices you or bring Dye Grenades to put up smokescreens.