Selkie

The Selkies are magical creatures introduced in Season 5.

Overview
For each planet connected with the Magic Dimension, it has a Selkie that guard the portals connecting the Ocean of Andros to the oceans of all the worlds and realms of the entire Magic Dimension. They are known as the gatekeepers. They have the ability to open or close the portals that link the Ocean of Andros to the oceans of another world or planet, and there is one gatekeeper for each world with the special symbols on their foreheads. The Selkies have the natural ability to communicate with underwater creatures.

The Guardian Selkies guard the Pillars of the Infinite Ocean, like the Pillar of Light, the Pillar of Balance and the Pillar of Control. They use golden spear-like weapons and do not have symbols on their foreheads.

Along with the gatekeepers (Selkies that have ability to open ocean gates) and Guardian Selkies (Selkies that guard the pillars in the Infinite Ocean), there are still many normal Selkies with unknown power. They are seen using weapons like the Guardian Selkies and the symbols on their foreheads are like the ones on tritons' foreheads.

There are often many round creatures looking like baby fish that accompany them which turn onto brightly colored fish on coming in contact with magic or other fish. They are called bollabies.

Physical Appearance
The Selkies of the Oceans are miniature wingless mermaids with brightly colored skin. They wear hats that are brightly colored like them and which have decorations and a kind of veil on the back. Only Gate keepers of all realms and Guardian Selkies of the Pillars have veil in their hat. Normal selkies have normal hair strands. Male selkies have their torso uncovered by scales. They are colored like the respective planets which they guard.

Ordinary Selkies have some similarities with the keepers:
 * The Selkies of Melody mostly have red and magenta hats with corals on it.
 * The Selkies of Earth mostly have yellow and orange hats with seaweed-like ribbons on it.
 * The Selkies of Solaria mostly have yellow and gold hats with stars on it.
 * The Selkies of Zenith mostly have lime and purple hats with line-like ribbons on it.
 * The Selkies of Linphea mostly have green and pink hats with flower decorations on it.
 * The Selkies of Domino mostly have cyan hats with horn-like decorations on it.
 * The Selkies of Andros mostly have blue hats with pearls on it.
 * The Selkies of Magix mostly have purple hats and hairs with butterfly decorations on it.

Season 5
The Selkies were first seen in "The Spill" during the crowning of Nereus, when Lemmy was holding the crown that King Neptune would place on Nereus' head.

After an oil spill occurred on Earth near Gardenia, oil from the spill traveled through the sea and reached the underwater portal linking the ocean of Earth to that of Andros. Phylla alerted by a Triton guarding vain and sealed the Earth portal after crossing it into Andros with the triton guard. There she and Lemmy saw Tritannus being mutated into a monster after absorbing the pollution and breaking free from the prison of Andros along with the Trix. With the help of the Trix and of the triton guards that he turned into monsters loyal to him, Tritannus stole the powers of the two gatekeepers. He then vowed to hunt down every Selkies and to steal all their powers, so that he would be able to enter the Infinite Ocean and from there conquer the whole Magic Dimension.

Six of eight known Selkies bonded with the Winx Club. Eventually Tritannus absorbed the powers of all the Selkies that guard an ocean portal, granting him access to the Infinite Ocean.

Selkies are also present in the Infinite Ocean, where there are Guardian Selkies who protect the Pillar of Light.

Magical Abilities
As stated before, their most well-known ability is opening and closing the ocean gates they guard. They do also possess generic abilities like shooting a beam and convergence. Desiryee, Flora's bonded Selkie and Keeper of Linphea's Ocean Gate has been seen magically growing underwater flowers.

Known Selkies

 * Desiryee (Linphea) - Bonded to Flora.
 * Sonna (Melody) - Bonded to Musa.
 * Illiris (Solaria) - Bonded to Stella.
 * Phylla (Earth)
 * Lithia (Zenith) - Bonded to Tecna.
 * Lemmy (Andros) - Bonded to Aisha.
 * Serena (Domino) - Bonded to Bloom.
 * Nissa (Magix)

Trivia

 * In Scottish/Irish and Faroese folklore, the Selkies are described as seal-men and seal-women, they live as seals underwater but have the ability to shed their skins to become human in land.
 * The Selkies are rumored to be the underwater equivalents of the Pixies.
 * The Selkies bear a certain resemblance to the Pixies and, due to their mermaid-like appearance and their small size, look like the Undines living in the Black Mud Swamp from Season 1.
 * A Selkie can detect whenever a fairy is nearby.
 * A Selkie guarding a planet's ocean gate knows her way around the ocean which she guards.
 * It is unknown whether a fairy can bond only with any Selkie from her home world or whether she can bond only with the Selkie that guards the ocean gate of her home world.
 * When fairy bonds with a Selkie from her respective home world, that also helps the Selkie to restore her power if it was taken from her and it also breaks spells/curses placed on people whom they bond with.
 * The Gatekeepers use the symbols on their foreheads as keys to open/close ocean gates and fight.
 * Apparently, the Selkie's symbol resemble their bonded fairy's power, except for Nissa and Phylla.
 * The normal selkies and Guardian Selkies use weapons to attack instead of the symbols on their foreheads.
 * When the Winx bond with the Selkies one of the other Winx will say "They're bonding".
 * The Selkies can also use convergence.
 * Like the Pixies, the Selkies have their villages. Interestingly, unlike the Pixies all live in only one village, the Selkies from different realms live in different villages.
 * All Selkies of all realms unite to fight Tritannus during "Battle for the Infinite Ocean".
 * "Selkies" were first rumored to be known as Piscies/Pescix.
 * Coincidentally, the word Piscies derived from the word "Pisces", which is the name for a zodiac, symbolized by two fishes.
 * The Selkies are named after the mythical creature of the same name.
 * In the planning stage, the Selkies have more similarities with the Pixies, with fish-like features, but were later changed.
 * The way the Clankies shoot beams from the gemstone on their forehead resembles the way the Selkies attack via shooting beams from the symbol on their forehead.