From the Super Mario Wiki
Anenomes are sea creatures with long, stinging tentacles and appear in the game Yoshi's Story. Anenomes act as stationary obstacles, moving their tentacles back and forth in an attempt to snare prey. Occasionally, Anenomes are found with the ability to move their arms in and out. They normally guard Melons and Heart Coins. Yoshi must dodge the tentacles and use his tongue to snag the goodies. Anenomes are invincible and cannot be defeated. They are only found in the level Lots O'Fish!.