Arcane elemental

Arcane elementals (also called arcane wraiths  and mana elementals ) are elementals composed of arcane energy.

They are beings of pure mana.

Mana surges are a type of arcane elementals, or another name for arcane elementals.

As a companion pet

 * Empowered Manafiend, Empyreal Manafiend and Energized Manafiend all come from rares in the uninstanced Highmaul in.
 * Glittering Arcane Crystal has a chance to drop from in the uninstanced version of Highmaul in.
 * Vibrating Arcane Crystal has a chance to drop from in the uninstanced version of Highmaul in Nagrand.
 * Warm Arcane Crystal has a chance to drop from in the uninstanced version of Highmaul in Nagrand.
 * Eldritch Manafiend and Erudite Manafiend are caught in Azsuna.
 * Kirin Tor Familiar is obtained by speaking to in his chamber in Dalaran, which can be reached using The Schools of Arcane Magic - Mastery after completing Higher Learning.
 * Mailemental achievement reward from Post Haste.

Speculation
Arcane elementals may or may not be actual elementals. Elementals are manifestations of their cores attaining raw physical forms, beings composed of the elements. Arcane elementals are composed of arcane energy, which is not currently considered a type of elemental energy.

Aluneth a powerful entity of pure arcane energy hailing from another realm of existence could be a arcane elemental.

Trivia

 * They have shapes that resemble voidwalkers/fire elementals, shades and voidwraiths.