Pillbug

From Wikitroid, the Metroid wiki

Pillbugs are small, insectoid creatures that crawl through spaces only accessible with the Morph Ball. They inflict little damage, and can be destroyed by being flipped over by a Bomb and then attacking the now vulnerable underside. A boss variation called the Spider Guardian appeared in Metroid Prime 2: Echoes as a Sub Guardian. In Metroid Prime 3: Corruption another variation appeared called the Phazon Pillbug, appearing only in one room on Bryyo.