Zoomer

Zoomers are semi-spherical mollusks with spikes along their backs similar to Geemers. Their intellect is limited to walking in set patterns along the terrain, meaning that Samus Aran must accidentally run or jump into them in order to be harmed.

The Metroid Prime Hunters logbook entry for the Zoomer states that it was the cause of a flesh-eating bacteria on Zebes which caused the extinction of many native species.

A creature similar to the Zoomer appears in the TRO section of Metroid Fusion.

There is also a talking pink Zoomer in a story of the Nintendo Comics System on-board the mechanical asteroid, Metroid.

Behavior
In all its incarnations, the simple-minded Zoomer is capable only of walking in set patterns. It will not directly attack Samus: she must instead accidentally touch one in order to take damage. The Zoomer is probably the weakest creature ever encountered in the series, indeed it is also the first creature ever encountered in the series.

Related to Zoomers are the more resiliant Geemers.

Metroid Game Manual
These fierce little creatures spray sticky fluid from their feet so they can move along the floor or up and down walls. There are two kinds: red zoomers and less powerful yellow zoomers.

Metroid Prime Logbook Entry
Morphology: Zoomer Anchors itself to walls and other surfaces. Avoid contact with spikes. A basic nerve center located directly above the Zoomer's mandibles detects nutrients. Sharp spines protect it from casual predators, but the lack of a reinforced carapace makes the Zoomer vulnerable to any indirect attacks.

Metroid Prime Hunters
Best known for breeding rapidly and carrying disease, ZOOMERS are responsible for the spread of flesh-eating bacteria on ZEBES, resulting in the extinction of many native species.