Well, most of the enemies are self explanatory.
Slasher: The most common type.
Leaper: Looks like scorpions.
Lurker: The baby ones.
Guardian: Stuck to walls.
Twitcher: Really REALLY fast Slasher.
Wheezer: Only appear in Hydroponics.
Pregnant: Self explanatory.
Dividers: Divvy up when killed.