A Space Pirate Trooper armed with a Photonic Power Scythe and a Quantum Assault Cannon. It appears that the weapon is mounted inside the right claw, as the weapon is not visible in this image but the weapon fire comes from this area.
The Quantum Assault Cannon is the primary weapon used by the Pirate Troopers in Metroid Prime 2: Echoes. In terms of operation, it is extremely similar to the Galvanic Accelerator Cannon that is used by the Space Pirates in the original Metroid Prime. When activated, it fires short bursts of yellow-orange energy bolts.
It is possible that the weapons are based off of Samus Aran's Power Beam, as their projectile appearances look nearly identical, as well as the fact that the Pirates had already reverse-engineered Samus's weaponry at the time that Metroid Prime occurred.
Appearance-wise, the cannon strongly resembles a Zebesian arm (which has similar functions). They could also resemble Ridley's head or even Crocomire's skull.