King Worm

The Deorem (also known as X-56V and King Worm), is the first boss Samus may face in Metroid: Zero Mission on planet Zebes.

Once Samus obtains her first Missile and heads back to the door, she will encounter this creature. It will entrap Samus by using its elongated body to block all exits and force her to fight it. The Deorem attacks by rushing its head towards its target, damaging her with its horns and spikes. The worm's second method of attack is to shake the segment of its body that is closest to Samus; several thorns which cover its body will start falling off and rain down on her.

All Samus has to do is fire a Missile at the creature when it opens its eye. Once Samus defeats it, she will obtain the Charge Beam. If the battle goes on for too long, however, Deorem will grow tired of fighting and leave.

If Samus does not kill Deorem in the first encounter (which is quite difficult to do in Hard Mode due to the bosses' enhanced vitality), she will encounter it at other times as she explores Brinstar. Samus will later encounter the Acid Worm in Kraid's Lair, so it is possible that Deorem will not be the first boss she defeats. Because this boss can be skipped, it is even possible to fight it after defeating Mother Brain. It will require one Super Missile to kill.

The creature also appears in the Metroid Zero Mission manga, but is defeated in a very different way. While fighting it, Samus notes that Zebes's entire ecosystem appears as if it "is trying to protect Mother Brain."

In the official Japanese website of Metroid: Zero Mission, this creature is named King Worm and is given the title Underground Demon.

Trivia

 * It is neither revealed nor explained how and why did this boss acquire the Charge Beam item. It's possible the Deorem unintentionally obtained it while digging through the tunnels of Brinstar.
 * Despite the Deorem having the Charge Beam, it never uses the item's abilities, contrary to other beings Samus encounters in her later missions who use their respective Chozo items in some shape or form. A logical theory would be that the Deorem has no beam weapon to begin with, thus making the Charge Beam item useless (one can easily imagine the Bomb item unusable without the Morph Ball). However, the boss' charge attack, in which it attempts to ram itself against Samus, can be a reference to the charge aspect of the item.