Acid Alien

From Alien Species

This creatures came from the Metroid universe. Though they have also been noted in the AVP Universe. In the video game: Aliens Unleashed (2006), Xenomorphs are seen spitting Acid Aliens out of their 'Maw' (AKA throught, toungue, or inner jaw). The Acid Aliens then lash onto a host, suck blood and then injest acidic 'blood' into the host, killing it. It then mutates into an Infectoid.