Diamondback Jellyfloat

The Diamond-Back Jellyfloat is very similar to a normal Jellyfloat, except for the purple and blue diamond on its back. Also its tentacles can reach out and sting your Pikmin, embedding a little spine in them that gradually kills them by injecting poison. This should give you a good reason to kill these first. Speaking of which.......

Captains
These hover too far off the ground to be attacked normally. Throw pikmin until this plummets to the ground to punch its lights out(a joke).

Pikmin
Throw Pikmin to the top side of the creature, the bottom side is the one with the tentacles. After it falls down swarm it for an easy win.

Trivia

 * This creature was not named for the diamond on its back, but for the poison it shoots out, which is similar to that of a Diamond Back Rattlesnake.
 * This creature is bio-luminescent, meaning its flesh produces light as a by product of some chemical reaction.
 * This creature has no known predators. It is assumed that those died out long ago because of the poison spines that almost instantly kill Pikmin.