This species was first described in 2007 after specimens were collected from the undersea volcanic ridge near the Kermadec Islands.

Adults are pale yellow, darker brown along their legs and setae, but because they live next to mineral-rich hydrothermal vent waters they are often coated with rusty ferric precipitate.

Gandalfus puia was first discovered along submarine volcanoes near the Kermadec Islands, making it the southernmost bythograeid recorded.

[2] This species was named by New Zealand marine biologist and carcinologist Colin McLay.

The genus name references Gandalf, the wizard character in The Lord of the Rings, the novel written by J. R. R. Tolkien and later filmed in New Zealand.