After the first door, in the middle of the following hallway you will trigger the opening of two chambers with enemies to your left and to your right. A third enemy will teleport in front of you. Return to the first room and turn around. To both sides of the door secret chambers (Sector 219) have opened. The western one contains a backpack, the eastern one a super shotgun. Both chambers count as one secret.
The walkway east of the Spider Master Mind's battle area (which is north of the lava area) leads to a plasma gun. Just open the wall behind it to reveal a Bulk Cell. (Sector 108)
From Secret #2, walk the way back to the Spider Master Mind's battle area. The exit of the hallway is blocked, so use the northern teleporter instead. After teleporting, walk back to the blockade, and unlock it from this side. Now go to the northern hallway and enter it. A secret room (Sector 205) has opened opposite the teleporter, containing two Bulk Cells, two Rocket Boxes, two Shell Boxes, a Soul Sphere, a Security Armor and a backpack.