This pops at the end of the battle just after you crash in the baths. This was a little annoying for me, so here's how I did it:
Run right from the ship into the next screen and then immediately crouch. Don't stand up until you kill all of them.
Take turns putting up a shield and firing a super blast. Shield/blast/shield/blast... then IMMEDIATELY run right when the last guy goes down. It might not work every time, but it's pretty solid. (Yeah, I died here about 20 times.)
If you're stuck, here's a visual walkthrough that someone made a while back.http://www.visualwalkthroughs.com/anotherworld/anotherw....htm