Bards, Druids & Rangers are shapers of prime and can share Primal Secrets.
PRIMAL SECRETS: At 1st level Bards & Druids can learn* two spells, and Rangers one spell, from the repertoire of another prime-spell-caster. Such a spell can be learned from any prime-spell-caster class including your own. The spell must be of a level you can cast, as shown on your spell-slots-table, or be a cantrip. When learned, the spell count as a spell of your own class, and are included in your number of Spells Known per day. Some such spells are not found on standard spell-lists; and only exists as Primal Secrets.
Druids & Rangers can only change one of their prepared spells per day.
* This does not include any non-prime-spell gained through the bards magical secrets feature.