From the Super Mario Wiki
Gooey Goons are blob-like creatures that hang from ceilings in Yoshi's Island DS. They come in a variety of colors and hang down from different heights. The Yoshis can't jump on these enemies, but they can turn them into eggs. Their primary method of attack is swinging back and forth at Yoshi, attempting to knock the baby off his back.
In the second boss battle of World 1, Kamek uses one of his magic spells to transform a yellow Gooey Goon into an over-sized tan Gooey Goon known as Gilbert the Gooey. Twenty multicolored Gooey Goons will cover him, and Blue Yoshi must eat them or destroy them to defeat him.
In the Island Museum, they are classified as subterranean enemies.