Instructions
Travel to the Seaweed Tower, and search for the Seruf. The Seruf is a giant pink clam with several seastars stuck to the outside of its shell. The Seruf can usually be found on higher levels of the Tower. If the Seruf has been recently defeated, you may need to wait a few minutes for it to respawn.
Get the Seruf to open its shell. When you first encounter the Seruf, it will be hiding within its shell. Hit the shell until the Seruf wakes up.
Defeat the Seruf. The Seruf has a lot of HP and a strong knock-back attack, so be ready for a long fight. There aren't any special moves or attacks that are especially effective against the Seruf. The only thing to do is hit it with your strongest attacks for as long as it takes. Once the Seruf is killed, you can claim its pearl for your own.