Arachnotron

The arachnotron (sometimes called Baby spider) is a monster introduced in Doom II. It is a smaller cousin of the Spider Mastermind that fires green plasma shots rather than bullets. Once the Arachnotron engages an enemy it will continue to fire until the enemy moves out of its field of view; or until the Arachnotron is hit with enough force to be moved, or killed. Similar behavior can be observed with the Chaingunner and Spider Mastermind.

According to the manual:
 * Maybe cybernetics wasn't such a great idea after all. Look what the demons have done with it. It seems unfair somehow you're not the only guy in Hell with a plasma gun.

Appearance statistics
The IWADs contain the following numbers of Arachnotrons: