I would imagine that conjurer unlocks black mage and thaumaturge unlocks white mage.

The reasons for this supposition are rooted in the lore:

Conjury is based on manipulation of elements and dealing with elemental spirits.
Thaumaturgy is centered around a religious organization dealing with matters of life and death.

SE has said they will be reevaluating skills and possibly reassigning some from one class to another. Rebalancing spell lists seems to fit in with this idea.