Ing Webtrap

Ing Webtrap is a rare enemy found in Metroid Prime 2: Echoes that appears only once in the entire game. Found in Dark Agon, they block both doors of Battleground when Samus battles a hoard of Warrior Ing for a Dark Temple Key. Once the Warrior Ing are killed, the Webtraps are removed from the doors and are never seen again, making them a one-time scan.

Metroid Prime 2 Logbook Entry
"These creatures respond to commands from the Ing, forming over areas as ordered. They are virtually indestructible, and can only be undone by killing the Ing that commands them."