that is a modular power distribution system....
actually, many different configurations can be created using this brand of components
the "box" above could be another terminal strip or hold relays, but is more likely and more commonly just a wire run to keep things organized.
in the photo, the fingers that can be seen on the bottom with the wires coming out from between them, all have a hook on the end of them that hooks into a groove in the cover... if you start at the end and push upwards on the fingers as you pull outwards on the lid, you will then be able to do this successively with all the fingers and release the cover/lid.... or release the fingers on top, whichever is easier to get to....
the ground buss as shown in the system is almost inadequate for a boat, so adding one that will accommodate your needs better will probably be necessary, but if not necessary, it will make it better to work with....