This is Blue Pikmin.
Info
Blue Pikmin, as their name implies, are a blue species of Pikmin that reside on PNF-404. Besides coloration, these Pikmin are distinguishable from other Pikmin species by their mouths, a trait seen in no other Pikmin species. These mouths are used to take in water, which filters oxygen through the gills located on their cheeks. This gives them the astonishing ability to live their lives completely underwater. Producing more Blue Pikmin can be easily done by dragging nutrients or animal carcasses to the Onion or by throwing other species into a Lapis Lazuli Candypop Bud.
Abilities
Only the Blue Pikmin, Bulbmin, and Winged Pikmin are able to safely traverse watery areas; any other color will simply flail around in panic before drowning (it has been observed, however, that certain Mushroom Pikmin can traverse water as well as Blue Pikmin can). While in water, the Blue Pikmin behave almost the same as they do on land. If they are idle and see a nearby Pikmin drowning in water, they will quickly run to them, pick them up, and throw them to shore. This action is often called the "Lifeguard Ablility." However, they will not rescue Pikmin if they are a certain distance away, so they can't always be relied on. This feature was removed in Pikmin 3. Blue Pikmin seem to be the most balanced Pikmin species; they have good attack power, durability, mobility and throw distance. As of Pikmin 3, Blue Pikmin can swim in schools to swarm aquatic enemies, which makes fighting enemies such as Water Dumples and Puckering Blinnows much easier.
Discovery
Blue Pikmin are the last species of Pikmin discovered in all three games. In Pikmin, their Onion is found in the Forest Navel. In Pikmin 2, 5 of them can be found near their Onion chasing after Wogpoles in the Awakening Wood in the same area where the Radiation Canopy was found in Pikmin. To gain control of them, Yellow Pikmin are required to break down the electrified gate. Throw them up onto the ledge, then run around to whistle them. However, there is a Cloaking Burrow-nit buried outside of the arena that the Blue Pikmin reside in, so be wary. In Pikmin 3, they are found in the Garden of Hope after rescuing Louie in the Twilight River. You must use the Winged Pikmin to pull the Blue Onion from the ground. They are often considered the least usefull Pikmin type, as most parts in Pikmin that seemingly require them can be obtained in another way. In Pikmin 2, a majority of the areas in the game can be reached without the need for Blue Pikmin. In Pikmin 3, Blues are the least useful and have little to no use in story mode, aside from getting 100% completion in the game by going back to the previous areas to collect the game's few submerged fruits.
Super Smash Bros. Brawl
Blue Pikmin appear in Super Smash Bros. Brawl as species of Pikmin that Olimar can pull from the ground via Pikmin Pluck, his standard special move. They are the only type of Pikmin that don't drown in the water. Blue Pikmin have good mobility, throw, and durability compared to other types of Pikmin (Purple Pikmin are very durable, but lack mobility, and throw), and withstand water moves like Mario's F.L.U.D.D., or Squirtle's water gun. Olimar is most likely to pull up a Blue Pikmin if he is on a water-based surface, such as a cloud or ice.