Hypselodoris festiva is a common species of colourful sea slug or dorid nudibranch, a marine gastropod mollusk in the family Chromodorididae. It eats sponges.
Hypselodoris festiva has a dark blue mantle with a central longitudinal yellow line, which may be broken, yellow spots and a yellow margin. The yellow spots may join up to form two more lines and in large individuals extra yellow spots develop between them. The rhinophores have blue shafts and red lamellae on the clubs. The gill leaves are translucent white with a single red line on the outer edge and red lines on the inner edges.
