Noncorporeal beings that need a living host, one of which haunted the women of Beverly Crusher's family for generations on Caldos.
Anaphasic lifeforms are noncorporeal beings that must bond with a living host to survive. One called itself Ronin and lived inside a candle, appearing to its hosts as a charming lover and sapping their strength over time.
In Sub Rosa, Beverly Crusher attended her grandmother's funeral on the colony of Caldos and learned Ronin had attached himself to the women of the Howard family for centuries. Ronin tried to make Beverly his new host, but she destroyed him with a modified phaser.