Shadow Pirate

From Wikitroid, the Metroid wiki

Shadow Pirates were Space Pirates fitted with a cloaking device that allowed them to become invisible to anything but the Thermal Visor. They have only appeared in Metroid Prime, though Echoes and Corruption featured pirates capable of turning invisible.

Shadow Pirates were limited to melee weaponry, as their cloaking devices drained too much energy to power the standard-issue arm cannons. They wore large purple helmets that obscured their entire faces, including their eyes, which featured a large translucent blue orb on the forehead. Its purpose is unknown, but it falls to the ground if a Shadow Pirate is incinerated by the Plasma Beam.

One Shadow Pirate appears without the ability to cloak, right at the entrance to the Glacier One facility. Oddly, the area over his eyes glow with fire like normal Pirates in Prime, despite his helmet covering them entirely.

They were most notably in the Space Pirate lab in Phendrana Drifts, but a few appeared in the Phazon Mines.