The Bull Squid is that annoying alien that spits acid, ate headcrabs, and could kill you at close range with one hit. He hasn't changed much, but you can tell the difference.
This old Bull Squid is in the water, just like he does now
Just a Bull Squid
This old Bull Squid is about to attack an old scientist
I'm not sure why, but the Bull Squid used to be yellow. Some people think that this is was a completely different alien and that his name was Bull Chicken because it was shy.
This is proof that this is probably a Bull Squid rather than a Bull Chicken because in this same spot in the real game is a Bull Squid