Bullsquid

Bullsquids (Taxonomic designation Gastropolypus toxophlegmata,[3]  or "Phlegm-shooting Many-legged-mouth") are a species of highly aggressive, bipedal creatures that appear throughout the Black Mesa Research Facility during the Resonance Cascade. Bullsquids are able to survive, if not thrive, in environments that are unfriendly or even toxic to humans, including sewers and pools of radioactive chemicals or biological waste. On Xen, Bullsquids are found drinking from Healing Pools.