They live in the oceans of the Magic Dimension and some are the guardians of the gates under the ocean. Tritannus stole their powers to get access to the Infinite Ocean. Their powers are restored when a fairy from their respective home planet bonds with them. Selkies can also sense when their bonded fairy is nearby. Based in part on the selkies of Gaelic folklore.
Serena: The gatekeeper of the ocean portal of Domino and Bloom's bonded selkie.
Illiris: The gatekeeper of ocean portal of Solaria and Stella's bonded selkie.
Desiryee: The gatekeeper of ocean portal of Lynphea and Flora's bonded selkie. She finds Sky's pendant of Eraklyon, which she gives to Flora.
Sonna: The gatekeeper of ocean portal of Melody. She is Musa's bonded selkie.
Lithia: The gatekeeper of ocean portal of Zenith and Tecna's bonded selkie.
Lemmy: The gatekeeper of ocean portal of Andros and Aisha's bonded selkie. She is the 1st selkie to have a bonded fairy and alongside Nissa are the first 2 selkies to appear in season 5.
Phylla: The gatekeeper of the ocean portal of Tir Nan Og. Roxy is rumored to be her bonded fairy but never onscreen.
Nissa: The gatekeeper of ocean portal of Magix. She doesn't have a bounded fairy onscreen but Daphne is rumored to be it.