Chu Worm

These foes are located in the Lakebed Temple as well as the Cave of Ordeals. You cannot harm them while they are in their bubble that they have formed around them. Use either your Clawshot to get them out of their bubble shield or use your bomb arrows to blow up the shield. Once the worm is out just slash away at it. They may be related in some way to the Gekko and Mad Jelly which appears in the Great Bay Temple in Majora's Mask.