Tenellia phoenix is a species of sea slug, an aeolid nudibranch, a marine gastropod mollusc in the family Fionidae.

[2] This species was described from La Jolla, California, United States.

It has been reported from Monterey Bay to Mission Bay (San Diego), California[3] and Costa Rica.

[4] Tenellia phoenix is a small translucent aeolid with swollen cerata and a visible central line of digestive gland which shows through the skin.

The oral tentacles and rhinophores are suffused with brown pigment.