The shell can also take any moons nearby, for example, when Earth was snatched from its system, the Earth's moon was also encased in a much smaller shell attached to the bigger shell Earth was in and was connected by some giant metal pole of some sort. It is a known confirmation that the Planet Jackers prefer planets with life on them to burn as one of them states that the ones with lots of critters on them burn good.
The Planet Jackers could be like the Irken race, an insectoid species due to their insect like eyes which almost except for color resembles Irken eyes. They too like the Irkens have green skin. Planet Jacker have huge rhinocerous like feet with two big hooves. Their space suits have strange tubes which go through their helmets to their mouths which probably contains fluids to keep them fully hydrated.