The ambusherpent had to cope with the new changes of environment. It did this by eventually evolving paler and nearly-white exoskeletons, which helped camouflage them and making them more efficient at hunting in the snow as opposed to its ancestors brown exoskeleton. The cold water forced them out of the water again and they regained their ability to survive above water again, albeit for short amounts of time of around one to two hours.
They benefit of this time by heating up again in the warm sun and ambushing species swimming past them. They use their three big eyes to spot faraway prey, while they dip downward facing hairs into the water, to feel vibrations of nearby prey. Once they have locked on to their prey, they will lunge for them and usually they'll succeed in their endeavor. They will also hunt on land, although they'll never stray too far away from the water and because of their sluggish movement, they will usually rely on camouflage.
Their horizontal jaws have grown, while their vertical jaws have shrunk due to their lesser usefulness to the ambusherpent and they've grown stubby little growth on certain segments that aid them at climbing on the ice and movement in the ice.