Geemer

A Geemer is a "cousin" of the Zoomer which, in Metroid Prime and Metroid Prime Hunters, is invulnerable to the Power Beam. When attacked in this fashion, it defends itself by protruding spines. The only way to destroy a Geemer in Metroid Prime Hunters is to shoot it with any of the six sub-weapons or a missile, and in Metroid Prime, to shoot it with a Missile or the Plasma Beam.

Geemers seem to have appeared in Metroid Fusion, as there is an X variant of a creature which bears a striking resemblance to them and shares the same characteristics mentioned above (see image), and any physical differences between them may have very well been caused by the X.

Geemers are also seen in Metroid Prime, where they look identical to red Zoomers but with fewer eyes. They follow a very similar AI modified for three dimensional movements.

In Metroid Prime 3: Corruption there are Geemers on Bryyo but no Zoomers. These Geemers have a more rounded body and fewer spines.

Interestingly, Super Metroid's code refers to Geemers as Zoomers, indicating that the "new species" was an invention of the translation team. Several other creatures changed names between the original game and Super Metroid, but only Geemers emerged as a separate species alongside the original in subsequent games.

Geemers return in Metroid: Other M as enemies in the Main Sector and the Biosphere. Hologram Geemers are also seen during the training sequence at the start of the game. They also occur in an ice form known as a Snomer throughout the Cryosphere. In this game they gain the ability of jumping and moving faster than they did in other games.



Artificial intelligence
The Geemer begins by moving in either the left or right direction. When the Geemer encounters a vertical wall, it rotates by 90 degrees and walks up the wall it hit. Conversely, if the Geemer walks off of a ledge, it rotates -90° and walks down the wall. This allows Geemers to move in simple circles around a complex room or object.

There is a flaw in the Geemer AI in the original Metroid. If the object the Geemer is standing on is destroyed, the Geemer continually spins in place, as the AI is constantly rotating by -90°. This is fixed in Super Metroid, as the Geemer unceremoniously falls to the floor, although that glitch can still be exploited if done with precise timing (the geemer/zoomer must be going onto or from the door to/from another surface and it will rapidly spin as if in the original Metroid).

In Super Metroid, a Geemer of the ordinary blue/purple type is one of the first enemies encountered. It does minimal damage. When Samus Aran fires a Super Missile at a wall or ceiling, the resulting shockwave causes all Geemers in the area to fall off the ledge they were on.

In Metroid: Other M, the Geemer's received an intelligence boost, and will actively follow Samus, instead of just going around like they did in Super Metroid.

Samus Geemer
There is also a unique quirk involving Geemers in Super Metroid. In Crateria, there is a small enclosed room on the right side, close to the Wrecked Ship. It is visible on the map as a small rectangle surrounded by a much larger room. When Samus enters this room, a Samus-colored Geemer that is orange and has green on the tips of the spikes is visible above her. This Geemer follows a different pattern from normal Geemers, as it will match Samus' horizontal movements on top of the tube. This Geemer can be killed by the Wave Beam, Grapple Beam (jumping & grappling as soon as Samus hits the celling will have the Grapple beam go through, and the Grapple beam can kill enemies) or Power Bombs, and the item dropped by it (usually energy or missiles, like any other enemy) can be collected via the Grapple Beam as well. Further, this particular passage can be approached from above, but when the player reaches it, the Geemer is absent. Since no programmer has specifically said why they put this Geemer here, it is likely that it is an easter egg. Also the Geemer will follow Samus' movements, even stopping in the same spot she stops at when it reaches her.

(1986 manga)
"This organism excretes a mucus from its legs while crawling on the rocks. The yellow Geemer can be destroyed with two shots from the normal beam. The red ones are destroyed with four."

Super Metroid manual
"Geemers crawl on floors and walls."

Super Metroid Nintendo Player's Guide
"Not powerful, Geemers walk steadily around various surfaces in a repetitive manner."