The Starnacle is a member of the Shellusk Family featured in Hey! Pikmin. The Starnacle is a starfish-like creature that usually serves as an obstacle in the path of Captain Olimar and his Pikmin during their underwater explorations. It is currently the only known member of the Shellusk family.
The Starnacle uses its three arms to block Captain Olimar's path. Olimar must use his Blue Pikmin to hit its arms and make them retract in its core, allowing the squad to progress further. After some time, the Starnacle will let its arms out once again.
Hey! Pikmin Log
"This mollusk-like creature's arms are long like an octopus's but tough like a starfish's. They withdraw when struck. The S.S. Dolphin II says he gets anxious at the sight of it, but I know better: those thin, gossamer arms are a real delicacy when properly prepared."