Catriona alpha is a species of sea slug, an aeolid nudibranch, a marine gastropod mollusc in the family Trinchesiidae.
This species was described from the shore of Kozuchi-jima near the Tamano Marine Laboratory, Tamano, Inland Sea of Seto, Japan; it also occurs off New Zealand.
The typical adult size of this species is 13âÂÂ15 mm.