We dont have any Infos about this Alien. The Alien only appears in Abikos Flashback. Its looks like a big Goat Demon and can shoot Dark Spikes. Its killls a lot of Gantzer. From the Picture its seems thats Fujimoto who has lost his Arm is killing the Alien with the Z Gun.
Maybe Fujmmoto and Abiko are the only ones who survive this Mission.