Dentalium Shell
From Starfy Wiki
The Dentalium shell (Japanese: ツノガイ, Tsunogai) is an obtainable item in Densetsu no Starfy. It's a colorful tusk shell.
On the quest to find Herman's missing home, Herman gives Starfy a Key which unlocks the barrier leading to the next room of Lobber's Cave. In the next room, Starfy finds the tusk shell in a small body of water. Starfy returns to show it to Herman, but the tusk shell is too small for him. Herman then teaches Starfy how to use his Star Spin so he can break blocks and search further.